# Abstracts Posters

Document Sample

					Abstracts Posters

Tuesday June 3

PAN-GCSS

17:00-19:00

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Title: A comparison of cloud resolving model simulations of trade wind cumulus
with aircraft observations taken during RICO

Presentation : BLC WG June 2
Poster nr1 : Tuesday June 3

Author: Steven Abel
Co-authors: Ben Shipway and Chris Smith

Trade wind cumulus clouds are prevalent over the subtropical oceans and are
commonly observed to precipitate. Whilst detailed cloud resolving model (CRM)
simulations have been shown to be a valuable tool for guiding parametrization
development of moist convection within GCMs, the importance of precipitation from
trade wind cumulus on the global climate remains poorly diagnosed, in part due to the
crude representation of the warm rain process within current models. There is therefore
the need to establish that CRMs are able to simulate realistic water budgets within the
trade wind cumulus regime in order to ascertain their usability in developing
parametrizations of precipitation fluxes.

The Rain In Cumulus over the Ocean (RICO) field campaign took place between
November 2004 and January 2005 around the islands of Antigua and Barbuda. A
comprehensive suite of in-situ observations were made during RICO, providing an
excellent tool for characterizing trade wind cumulus on scales ranging from the
microphysical to the cloud field ensemble.
This paper presents comparisons of some cloud field statistics derived from the three
research aircraft that participated in RICO with those derived from numerical
simulations performed with the Met Office CRM.
The variation of updraft velocities, cloud liquid water content, and precipitation loading
as a function of altitude above cloud base are shown, and the sensitivity of the
simulations to different cloud microphysical configurations examined.

The comparisons show that the model is unable to represent the observed variation in
the water content of precipitation sized droplets when using a single-moment bulk cloud
scheme. Treating the precipitation sized droplets in a double-moment sense brings the
model into better agreement with the observations. However, the simulations are highly
sensitive to the prescribed cloud droplet concentration used in the autoconversion
process, highlighting the importance of quantifying the aerosol conditions of the regime
under investigation. In order to better assess the sensitivity of the model simulations to
different aerosol properties and loadings we have developed a new double moment
cloud droplet scheme which will be assessed against the RICO observations.

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On cloud droplet condensational growth, spectral dispersion, cloud
optical properties, and precipitation in shallow marine convection

Andrew Ackerman
NASA Goddard Institute for Space Studies
New York, NY 10025
USA
andrew.ackerman@nasa.gov
+1-212-678-5675

Poster nr. 2      : Tuesday June 3

Abstract:

The so-called Twomey effect is amplified or diminished when increasing
droplet concentrations in turn increase or decrease the relative
dispersion of cloud droplet size distributions. Results from a number of
observational and theoretical studies of stratocumulus conflict over
whether relative dispersion increases or decreases as droplet
concentrations increase. The dispersion of cloud droplet size
distributions also affects the sedimentation rate of cloud water and the
production of drizzle. Bin microphysics models used in large-eddy
simulations, including those used in previous studies of cloud droplet
spectral dispersion, typically ignore the solute and Kelvin effects on
droplet condensational growth. We find that an artifact of doing so is
that the relative dispersion of droplet size distributions always
increases with CCN-induced increasing droplet number concentrations.
Including those terms results in that tendency reversing when the
collision-coalescence process becomes inactive. We also present results
that explore the effect of cloud droplet spectral dispersion on
precipitation, and the resulting sensitivity of cloud properties to
changes in CCN concentrations. The simulations are based on idealized
case studies of marine stratocumulus and trade cumulus from field
campaigns.

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Evolution of the tropical atmosphere (20S – 20N) radiative budget as seen from
observations and AR4 model simulations.

Natalia Andronova
University of Michigan

Poster nr3 : Tuesday June 3

A transient change in the balance between the incoming and outgoing radiation is an
important indicator of the changing Earth’s climate.
We use available data from satellites (from 1980 to present) and ground measurements
(from 1995 to present) to reconstruct the long- term evolution of the energy budget of
the tropical atmosphere (20S-20N). We compare this estimate of the radiative budget at
the TOA with the corresponding estimates obtained from model simulations from the
AR4 database. We show that in spite of the dramatic increase in the model’s ability to
simulate past and recent temperature change, the models show different sensitivities to
the Mt. Pinatubo eruption and do not agree with observations of the overall radiative
balance tendencies over 1980-2000.

Co-authors:
Joyce E. Penner and Li Xi
University of Michigan,
Takmeng Wong
NASA Langley Research Center
William Collins
Lawrence Berkeley National Laboratory

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A CALIOP view on Low Clouds

C. Antoniazzi and B. Stevens
UCLA, Dep’t of Atmos. & Oceanic Sciences., Los Angeles, USA

Tuesday June 3: Poster nr. 4

Abstract

Two winters (DJF) of high-resolution (1/3 km) cloud retrievals from the CALIOP lidar flown on
CALIPSO are analyzed and compared to general circulation models and ISCCP data.
Preliminary findings include: pronounced diurnal cycles in low clouds; unusually extensive
areas of low cloud tops (< 2km) over the subtropical oceans in the summer hemisphere; no
evidence of multimodal shallow convection, but distinct evidence of a freezing level maximum in
cloud occurance.

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A study of the microphysical and macrophysical properties of cirrus: An
intercomparison between Cloudsat, in situ measurements, a GCM and an ice
crystal model.

Anthony J. Baran, R. Cotton, C. Lee, A. Bodas-Salcedo, J. Bornemann, E.
Hirst, R. Austin, J. Haynes, and G. L. Stephens.

Poster nr. 5: Tuesday June 3

In this paper we present a comprehensive intercomparison between CloudSat derived
cirrus IWC and ice crystal effective dimension (De) and aircraft in situ sampling of these
quantities as well as model predictions of IWC and De. During the Winter and Autumn
of 2007 three flights took place as part of the CAESAR (Cirrus and Anvils: European
Satellite and Airborne Radiation measurements project) campaign of flying in, above
and below cirrus around the United Kingdom using the FAAM (Facility for Airborne
Atmospheric Measurements) BAE-146 G-LUXE aircraft. All three flights were coincident
with the A-train and were particularly designed for CloudSat overpasses. Coincident
flights took place on the 16th and 25th of January 2007 and on 20th September 2007.
The cloud physics suite of instruments included the new SID II (Small Ice particle
Detector) which can measure the particle size distribution function (PSD) between 3
mm and 100 mm, particle number concentration, particle phase, size and estimate of
IWC. The 2D-C and 2D-P probes, the 2D-C overlaps with SID II. The 2D-C was also
used to estimate the IWC as well as De. A direct measure of the IWC was obtained
using the Nevzorov probe. In all three flights the aircraft sampled the cirrus as a series
of profiles from cloud-top, which was penetrated in all three cases, to cloud-bottom and
as a series of saw-tooth manoeuvres. These manoeuvres were performed in order to
obtain a good statistical sample of the macrophysical and microphysical state of the
cirrus with which to compare against CloudSat and models.
For each case the CloudSat PDF's of retrieved IWC and De are compared against the
in situ measured PDF's and the CloudSat integrated IWC is compared against the in
situ sampled integrated IWC obtained from the aircraft vertical profiles. From the
derived IWP and mean De the total visible extinction optical depth is estimated from
CloudSat and aircraft probes. These radiative results are compared. PDF's of IWC and
De for the same three cases are obtained from the U. K. Met Office global and
mesoscale NWP models and these are compared against the CloudSat and in situ
derived PDF's. Prediction of IWC and De from a self-consistent model of cirrus is also
tested against the aircraft vertical profiles of these quantities. The global radiative
impact of the new cirrus model and its implications will also be discussed.

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Evaluation of the atmospheric boundary layer in ACCESS using ensemble Single
Column Model validation

Vaughan J. I. Barras, Peter J. Hurley, Ashok K. Luhar
Centre for Australian Weather and Climate Research, Melbourne, Victoria, Australia

Poster nr. 6: Tuesday June 3

Introduction
The Australian Community Climate and Earth System Simulator (ACCESS) is currently
under development as a joint initiative of the Bureau of Meteorology and CSIRO in
close partnership with the UK Met Office. The atmospheric component of ACCESS is
an up to date version of the Unified Model (UM) that has been developed and used by
the UK Met Office for both operational Numerical Weather Prediction (NWP) and
climate prediction.
Of particular interest has been the validity of the boundary layer parameterizations
under strongly stable conditions and low wind-speeds (< 2m/s). As part of the testing of
the CSIRO meteorological and air pollution model TAPM (Hurley et al, 2005), Luhar et
al. (2007) examined near-surface observations of such conditions using data from the
CASES-99 field campaign and the UK Met Office Cardington monitoring station. It was
found that the commonly used Monin-Obukhov similarity relationships were not
consistent with the observations under strongly stable conditions. The recent inclusion
of a modified stability function for momentum, which is based on a power-law type
scaling in TAPM has improved the prediction of the frequency and intensity of low wind
conditions occurring under very stable conditions in accordance with observations. In
light of this, it is of considerable interest to similarly test the surface-layer
parameterizations within the UM.

Ensemble SCM validation
Single Column Models are an effective tool in the development and testing of model
parameterizations. However, they do rely upon the prescription of a number of large
scale forcing fields, particularly advective tendencies and vertical velocity. When
comparing model results with observations, errors may arise from the model
parameterizations or from inaccuracies in the prescribed forcings, therefore some
separation of the effect of each is required. Hume and Jakob (2005) sought to address
this by using an ensemble approach combining a range of NWP-derived model forcing
datasets and applying them to two different SCMs. From this, uncertainties in the SCM
simulations arising from the forcing data were able to be identified as well as
deficiencies in model parameterizations using standard ensemble validation techniques
(Hume and Jakob, 2007).
Ensemble SCM validation is a valuable approach in the testing of GCM
parameterizations. The assembly of SCM forcing datasets from a number of different
NWP sources has been adapted such that ensemble SCM runs may be performed for
any case where NWP analyses are available. As a basis for the testing of the near-
surface layer parameterizations in the boundary layer, SCM forcing data have been
derived from three reanalysis datasets (ERA-40, NCEP and JRA) and from analysis
fields from the Bureau of Meteorology’s Global Assimilation and Prediction (GASP)
GCM. The period from the CASES-99 field study has been chosen for initial testing as
there were a number of periods where boundary layer conditions were strongly stable
with weak, intermittent turbulence providing a good test of the model representation of
the near-surface wind-speed. It is known that models that parameterize near-surface
processes using Monin-Obukhov similarity theory struggle to represent these conditions

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accurately. Although here being applied specifically to alternative surface scalings, the
ensemble SCM validation approach provides a useful general framework for the
evaluation of alternative model paramterizations.

References
Hume, T., and C. Jakob, 2005: Ensemble single column modeling (ESCM) in the
tropical western Pacific: Forcing data sets and uncertainty analysis. J. Geophys. Res.,
110, D13109, doi:10.1029/2004JD005704.

Hume, T., and C. Jakob, 2007: Ensemble single column model validation in the tropical
western Pacific. J. Geophys. Res., 112, D10206, doi:10.1029/2006JD008018.

Hurley, P. J., W. L. Physick, and A. K. Luhar, 2005: TAPM: A practical approach to
prognostic meteorological and air pollution modelling. Environ. Modelling and Software,
20, 737-752.

Luhar A., P.J. Hurley, and K. N. Rayner, 2007: Modelling low wind-speed stable
conditions in a prognostic meteorological model and comparison with field data. Proc.
11th Int. Conf. Harmonisation within Atmospheric Dispersion Modelling for Regulatory
Purposes, Cambridge (UK), 2007.

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Clouds and Mid-latitude Storminess: A New Dataset

Poster nr. 7: Tuesday June 3

Michael Bauer
NASA Postdoctoral Fellow
NASA Goddard Institute for Space Studies
New York, NY 10025 USA

E-mail: mbauer@giss.nasa.gov
Phone: (212) 678-5512
FAX: (212) 678-5552
Office: 316C

Abstract: We introduce a new dataset/tool for examining cloud properties from a
phenomenological perspective. This new dataset, The MAP Climatology of Mid-latitude
Storminess (MCMS), essentially provides a detailed 6 hourly assessment of the areas under
the influence of mid-latitude cyclones and those that are not.

The MCMS project begins with a cyclone detection and tracking algorithm using the 6 hourly
sea level pressure (SLP) fields from the NCEP/NCAR Reanalysis (1948-07). From this list of
cyclones we then seed an outward search algorithm that locates the perimeter of each
cyclone (defined as the outer-most closed SLP contour containing only that cyclone).
Allowances are also made for situations where an even broader set of closed contours
envelope multiple cyclones.

We then pair this cyclone-domain dataset with relevant observations of interest (such as
ISCCP data) to ask interesting questions such as how do cyclone associated cloud
properties change with cyclone size, surface intensity, cyclone life-cycle or proximity to other
cyclones? This is done using the cyclone-domain to extract adaptive composites from the
observations. The cyclone-domain dataset can also act as a mask to ask similar questions
about the observations presumably not under the influence of a near-by cyclone. The MCMS
method also works on GCM output and allows for useful comparatives (either against
observations or model modifications). Many of these ideas are presented as examples.

Audience: The Extratropical System Working Group.

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Validation of turbulence and convective schemes on western Africa; comparison
of LAM and CRM simulations on a HAPEX-Sahel case study.

Poster nr. 8: Tuesday June 3

Beau I., Pollack D. (Météo-France, Ecole Nationale de la Météorologie, Toulouse,
FRANCE)
Guérémy J.F (Météo-France, Centre National de Recherches Météorologiques,
Toulouse, FRANCE)

The aim of this work is to analyse the behaviour of turbulence and convective
parameterizations included in the Météo-France ALADIN-CLIMAT Limited Area Model
in the frame of a 24 hour simulation of a HAPEX-Sahel case study, in comparison to
observations and to a CRM (Méso-NH, with a 5 km horizontal grid-mesh) simulation
carried out under the same boundary forcings. This framework provides an intermediate
step of parameterization validation between the Single Column Model and Global
Climate Model simulation studies.
The chosen case study is the 21st August 1992 over a 12° x 12° region centred over
SW Niger. It is characterised by the life cycle of a westward propagating convective
system associated to an African Easterly Wave. Both LAM and CRM simulations have
been performed over the same considered domain, using the same ERA40 boundary
forcings. Sensitivity tests to resolution have been first carried out with ALADIN-CLIMAT.
Second, the two different convective schemes used in ALADIN-CLIMAT show two kinds
of response mainly due to their different formulations of triggering (no constraints in the
dry layer under the convective cloud versus continuous treatment of convection
including this dry layer) and closure (moisture convergence versus CAPE). Third, the
impact of entrainment at the top of the PBL (included in the turbulence scheme) will be
shown.

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Advances in Simulating Atmospheric Variability with the ECMWF model: From

Peter Bechtold Martin Koehler Thomas Jung Martin Leutbecher and Frederic Vitart

Poster nr. 9 : Tuesday June 3

Advances in simulating atmospheric variability are presented that stem from revisions the
physical parametrisations for conevction and diffusion. The presentation includes
comparisons between simulation, observations and analysis data on mean climate, tropical
waves, and midlatitude synoptic activity

extra info:

in case that contribution is considered as poster: the above will be precise content
in case that it is considered as oral contribution and there is time, the importance of subgrid
physical parametrisations for the global energy cycle, and constraints of physical
parametrisations in the data assimilation context might also be shortly addressed
--

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Alan Blyth, Jason Lowenstein, Stewart Davies and Ken Carslaw, University of Leeds.

Poster nr. 10: Tuesday June 3

One of the key problems in cloud physics is still to quantitatively explain the warm rain
process. The problem has remained unsolved for so long mainly because observations
that are required of the detailed growth rates of the cloud drops have not been good
enough to compare with the models.

In this talk, we will show that the rate of production of warm rain, as observed in
shallow cumulus clouds during the highly successful Rain in Cumulus Over the Ocean
(RICO) field campaign, can be explained using the Leeds Model of Aerosol and
Chemistry (MAC3) 2-D axisymmetric cloud model using only the observed sub-cloud
aerosol size distribution ingested into cloud base.

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Session: 2 (New observations) or 4 (Cloud-climate feedbacks)

Evaluation of clouds in the Met Office global forecast model using CloudSat data

A. Bodas-Salcedo (1)
M. J. Webb (1)
M. E. Brooks (2)
M. A. Ringer (1)
S. F. Milton (2)
D. R. Wilson (2)
K. D. Williams (1)
(1) Met Office Hadley Centre, Exeter, United Kingdom.
(2) Met Office, Exeter, United Kingdom.

Poster nr. 11: Tuesday June 3

Clouds and their radiative properties are still not sufficiently well represented in numerical
weather prediction (NWP) and climate models. Improving their representation is a key
priority, as clouds play a main role in the Earth's radiation budget and are a key uncertainty
in predictions of climate change. CloudSat is the first spaceborne millimetre wavelength
radar (94 GHz) that provides estimates of cloud condensate and precipitation globally. We
have developed a system to simulate CloudSat data in the Met Office Unified Model (MetUM)
that is consistent with the observations. We apply this simulator to evaluate the simulation of
clouds in MetUM global forecast model, as previous studies have shown that the global
forecast model is a useful framework in which to analyse cloud representation errors that are
relevant for both numerical weather prediction and climate time scales.

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Session: Breakout session 6 (Cloud Climate Feedback Project)

Pilot intercomparison projects using the CFMIP ISCCP/CloudSat/CALIPSO Simulator

A. Bodas-Salcedo, M. J. Webb
S. Bony, H. Chepfer, J-L. Dufresne
(Laboratoire de Météorologie Dynamique/Institut Pierre Simon Laplace)
S. Klein, Y. Zhang
(Lawrence Livermore National Laboratory)

Poster nr. 12: Tuesday June 3

The CFMIP ISCCP/CloudSat/CALIPSO Simulator (CICCS) is a software tool that enables
numerical models to simulate data from the space-borne radar and lidar instruments
CloudSat and CALIPSO. The development of CICCS has been a collaborative effort from
several groups in the US and Europe, and will help climate modellers to make best use of
this exciting new data source. Several pilot intercomparison projects using CICCS are
currently underway, based on simulations with atmosphere-only models forced with
climatological SSTs. These pilot intercomparison projects will examine the sensitivity of the
results to different configuration choices of CICCS and study the representation of clouds
and precipitation in different models (e.g. vertical distribution of hydrometeors, dynamical
regimes, cloud clustering). In this talk, a description of the simulator and the pilot
intercomparison projects will be presented.

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A Possible Role for Immersion Freezing in Mixed-Phase Stratus Clouds

Gijs de Boer, Tempei Hashino, Gregory J. Tripoli, Edwin, W. Eloranta
The University of Wisconsin - Madison

The persistence of mixed-phase stratus clouds at high latitudes remains as an unexplained
phenomenon in both theoretical and observational circles. These common thin cloud
layers have been observed to persist for several days at a time at several Arctic locations,
exhibiting both a continuous liquid layer and precipitating ice throughout this period.
This cohabitation of the liquid and frozen phases contrasts with common theory, which
would dictate that the presence of ice would rapidly deplete the layer of it’s liquid, and a
complete glaciation would occur. This glaciation of the cloud layer and an under
prediction of liquid water has been shown to exist in numerical simulations of these
structures. Another interesting observation is that these layers have been observed in
areas where very few ice forming nuclei (IN) have been detected, leading to the
assumption that this ice is not being formed through traditional contact or depositional
freezing.

The lack of IN measurements have led some researchers to hypothesize that immersion
freezing may play a major role in explaining how ice and liquid persist over extended
time periods. Since immersed IN are very difficult to detect with current instruments,
these aerosols may have gone undetected. This paper will introduce a conceptual model
for the lifecycle of ice and liquid within these clouds. We will evaluate the likelihood of
immersion freezing playing a major role in the lifecycle of these cloud structures through
a combination of observational and numerical studies.

Observations utilized include those from long-term deployments to two Arctic locations.
Instruments included in these deployments include a suite of ground-based remote
sensors, such as a Millimeter Cloud Radar, High Spectral Resolution Lidar, AERI and
Microwave Radiometer. To support and expand upon the local, ground-based view of
these structures, the CALIPSO and CloudSAT space-born instruments are utilized as
well.

In addition to information gathered from the observations, sensitivity experiments
completed at the Large-Eddy simulation (LES) scale using a size-resolving microphysical
scheme are also reviewed for evidence pertaining to the role of immersion freezing. A
new immersion freezing parameterization that utilizes both temperature and soluble
fraction of a liquid drop to determine whether or not this particle should form ice is
applied to the mixed-phase stratus scenario. A combination of the observational and
theoretical work results in an improved understanding of the likelihood of immersion
freezing being a controlling nucleation mechanism within these cloud structures.
Heating and moistening over the southern quadrilater of the AMMA experiment

Dominique Bouniol 1, Lucas Besson2, Yvon Lemaître2, Mathieu Nuret1 and Alain Protat3
1
CNRM/GAME, Météo-France/CNRS, Toulouse, France
2
CETP, CNRS, Vélizy, France
3
BOMRC, Melbourne, Australia

Poster nr. 14: Tuesday June 3

Tropical convection, in particular over the African continent, plays a significant role in
global redistribution of heat, moisture and momentum. For instance, latent heat release
in deep cumulonimbus clouds in the ITCZ over Africa represents one of the major heat
sources on the planet.
Data collected during the Special Observing Period (1 June - 30 September 2006) of
the AMMA experiment are used in order to estimate heating and moistening profiles
over the AMMA southern quadrilater (centered in Parakou with Niamey, Tamale,
Cotonou and Abuja defining the four edges). The radiosondes regularly launched from
these five sites consist in the main imput to a variational analysis (named MANDOPAS)
as well as other data sets (obtained from ground-based instrumentation or satellite). A
particular attention is given to the two high frequency sonding periods where the dayly
As a first step the variational analysis has been evaluated against another objective
analysis method showing results in very good agreement for basic fields and in the
same range for moistening and heating profiles, in spite of major differences either in
the analysis process or in the amount of data included in the analysis.
A step by step analysis of the AMMA-SOP data has been undertaken, beginning by the
analysis of the radiosonding data and then sequencely including other data sets. A
particular attention will be given to the potential humidity bias of the rawinsonde data
set.
Basic fields will be analysed in regards to the convective activity within the quadrilater
as signed by other data sources.

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Low cloud feedback mechanisms in a superparameterized GCM and their
plausibility

Christopher S. Bretherton, Matthew C. Wyant, and Peter N. Blossey
Department of Atmospheric Sciences
University of Washington
Seattle, WA USA

Poster nr. 15: Tuesday June 3

A Cess-type climate sensitivity study indicates the superparameterized CAM3 climate
model (SP-CAM) has strongly negative low cloud feedbacks (Wyant et al. 2006 GRL).
In this approach, control simulations with present-day SST are compared with
simulations having SST uniformly raised by 2K. This method has proven to be a quick
and fairly reliable predictor of globally-averaged cloud feedbacks with doubled CO2 and
an interactive ocean.

We physically analyze these cloud feedbacks over the low-latitude oceans by sorting
the results into boundary-layer cloud regimes based on deciles of monthly-mean lower
tropospheric stability. We then perform CRM simulations in a column-modeling
framework using the composite large-scale forcing from the binning analysis.

Our binning analysis suggests that low cloud feedbacks in SP-CAM are due to the
in the +2K climate, both of which promote more boundary-layer cloud. The stronger
trade inversion is due to the stabilization of the moist adiabat in a warmer climate, while
increased longwave radiative cooling is due to the warming of the moist, cloudy,
emissive boundary layer.

Our column modeling uses exactly the same 2D CRM as used in each column of SP-
CAM, but allows us to experiment with a variety of resolutions. In each case, the CRM
is run to statistical equilibrium with the bin-mean large-scale forcings and SST from the
control and +2K SP-CAM runs. At the same resolution as used in SP-CAM, the CRM
roughly reproduces the cloud feedbacks seen in the SP-CAM. In higher-resolution
runs, the negative cloud feedbacks persist but are weaker. This suggests that the
negative low-cloud feedbacks in SP-CAM are strongly exaggerated due to under-

We propose that our binning/column-modeling approach is a useful general approach to
understand subtropical low cloud feedbacks in other climate models as well, and that
with somewhat higher but computationally affordable resolution, the SP-CAM would be
quantitatively useful in understanding subtropical low cloud feedbacks.

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Aspects of the diurnal cycle in climate simulations with parameterized and explicit
convection

Authors:     Peter Brockhaus, Cathy Hohenegger, Daniel Lüthi, Christoph Schär

Affililiation: Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland

Poster nr. 16: Tuesday June 3

We analyze the ability of the regional climate model CLM to simulate the European summer
climate at 50km resolution, with particular consideration of mean diurnal cycles of
precipitation, surface variables, convective indices and vertical profiles. We consider three
sets of simulations using different convective parametrizations (Tiedtke, Tiedtke-CAPE and
Kain-Fritsch), each covering six summer seasons (April-September). All simulations are
driven by ERA-40 reanalysis. Analysis shows that the afternoon peak of precipitation occurs
3-7 hours too early in the model, which may be linked to a strong underestimation of
convective inhibition. We also observe an underestimation of the diurnal temperature range
and a cold bias of about 1-3K, resulting in a too shallow boundary layer. In addition, the
boundary layer is found to be too well mixed and the night-time inversion to be strongly
underestimated.

As a possible future approach to improve the diurnal cycle of precipitation, we also test the
suitability of cloud-resolving resolution for climate applications. We conduct a one-month
integration (July 2006) at 2.2km resolution with explicit convection. Compared to its driving
coarse-resolution integration, it delays maximal convective precipitation by about 2 hours and
slows down the decay of convective activity in the afternoon. On the other hand, the high-
resolution integration often lacks precipitation in cases of weak synoptic forcing and/or over
flat terrain. An adapted treatment of sub-grid-scale clouds could help to overcome this issue.

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Recent Measurements of Heterogeneous Ice Nucleation on Ambient Aerosols

Sarah D. Brooks, Adam Fornea, and Andrew Glen
Texas A&M University

Poster nr. 17: Tuesday June 3

Heterogeneous ice nucleation events are a strong function of the availability and
composition of ice-nucleating aerosols (IN). Participation in field campaigns in 2008
have provided us with the opportunity to compare and contrast heterogeneous
nucleation on aerosols with a range of compositions. Further, multiple ice nucleation
mechanisms including contact, immersion, and evaporative freezing can contribute
substantially to ice formation under various atmospheric conditions. Here we report the
ice freezing temperatures facilitated by Saudi Arabian desert dust, soot, soil, and
volcanic ash. In these studies, a microscope apparatus equipped with a cooling stage
and a CCN video camera was used to observe the freezing temperatures of the various
samples. The humic material was the most effective IN with an average contact
freezing temperature of -7 °C, followed by volcanic ash which froze -9.8 °C. The overall
trend in effectiveness of the respective IN agrees with the trend in contact angles of the
three compositions. Mechanistically, these results are in agreement with a modified
classical nucleation interpretation of surface-driven heterogeneous nucleation. In
addition, freezing mechanism-IN composition relationships will be discussed to lend
context to the conditions under which each mechanism may play a significant role in ice
formation processes in the atmosphere.

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Entrainment and mixing in warm convective clouds: effects on droplet spectra
and on the onset of precipitation.

F. Burnet and J.-L. Brenguier, Meteo-France/CNRS, Toulouse, France.

Poster nr. 18: Tuesday June 3

During the SCMS-1995 experiment, three convective cells were sampled by the Meteo-
France Merlin-IV research aircraft at successive steps of their life time.
Thermodynamical and microphysical measurements are examined to document the
evolution of their properties from the initial stage of a young vigorous ascending cell up
to the decaying stage.
It's shown that dry air penetrates the cloud cells progressively thus producing
evaporation and cooling. Homogenization from the turbulence further occurs and finally
the cell collapses with a uniform negative buoyancy.
The coalescence process is triggered in one cell that leads to production of significant
precipitation. This cell is investigated in details to document the transition and to
identify the relevant parameter involved in this process.

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Impacts of Cloud-Radiation Interaction on Seasonal Simulation

Young-Hwa Byun¹, Suryun Ham¹², Song-You Hong², and Jhoon Kim²

¹ National Institute of Meteorological Research, Korea Meteorological Administration,
Seoul, Korea
²Department of Atmospheric Sciences, Yonsei University, Seoul, Korea

Poster nr. 19: Tuesday June 3

to different precipitation physics packages in seasonal simulation. Global model utilized
for seasonal simulation is a version of the National Centers for Environmental
Prediction (NCEP) Global Spectral Model (GSM) (Kanamitsu et al. 2002). Four
experiments in this study are designed with two cloud microphysical processes under
two different convective parameterization schemes. For representation of stratiform
precipitation physics, the Weather Research and Forecasting (WRF) Single-Moment 1-
class (WSM1) (Hong et al. 1998) and 3-class (WSM3) (Hong et al. 2004) microphysics
schemes are utilized. Also, the Simplified Arakawa-Schubert (SAS) scheme (Pan and
Wu 1995; Hong and Pan 1998) and National Center for Atmospheric Research (NCAR)
Community Climate Model (CCM) scheme (Zhang and McFarlane 1995) are used for
convective precipitation processes.
These four experiments are performed under Single Column Model (SCM)
framework for preliminary investigation about impacts of different precipitation physics
on the cloud-radiation interaction. Also, the GCM framework is used for further
investigation of their sensitivities to climate simulation. In this study, we expect that a
detailed evaluation of the simulated climate from a cloud-radiation feedback point of
view will shed lights on the physical reasoning on the sensitivity of the simulated
climate to the different physics package. Relative importance of the convective and
stratiform precipitation physics on the radiative properties will also be investigated. As
well, feedback between the stratiform precipitation physics and large-scale features will
be examined.

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Preliminary validation of GPCI simulations with observational data from NASA's
A-Train Aqua, CloudSat and Calipso satellites.

S. Cardoso(1,2), J. Teixeira(3), P. Rasch(1), P. Miranda(2), A. Gettelman(1), Y. Zhang(4),
S. Klein(4), J. Mace(5), C. Hannay(1), M. Koehler(6), M. Zhao(7), P. Siebesma(8), P.
Marquet(9), A. Lock(10), C. Jakob(11), C. DeMott(12), H. Kitagawa(13), D. Mironov(14)
(1) NCAR, USA; (2) CGUL, Portugal; (3) JPL, USA; (4) LLNL, USA; (5) University of
Utah, USA; (6) ECMWF, UK; (7) GFDL, USA; (8) KNMI, The Nederlands; (9)
MeteoFrance, France; (10) UKMO, UK; (11) BMRC, Australia; (12) CSU, USA; (13)
JMA, Japan; (14) DWD, Germany

Poster nr. 20: Tuesday June 3

The GPCI (GCSS/WGNE Pacific Cross-section Intercomparison), is a model
intercomparison project that has collected output from as many as 23 different GCMs
from several international groups active in climate research. The database of model
results describes the atmospheric physics in the Eastern Pacific sector of the Hadley
Cell. Systematic analysis of that data set, based on extensive comparisons between
model parameters and different observations is being perfomed. This type of model
evaluation aims at complementing the more traditional efforts in GCSS as the
SCM/LES/CRM methodology does not allow for feedback to the large-scale dynamics.
The main focus of the research is the representation of convection and clouds by global
models in two remarkable areas of the global circulation: the subtropical region of
stratocumulus and the deep convection belt near the Equator (as well as the transition
between them). A step forward has been taken in GPCI relatively to other similar
intercomparisons in regard to the use of high temporal resolution model results (every 3
hours for JJA 1998 and 2003) and observational data. This will be particularly important
in trying to understand boundary layer mixing and convection, and particularly the
transition from cloud-topped boundary layers (stratocumulus to cumulus) to deep
convection in the low-latitude marine environment.

In this work we use information on relative humidity (RH) in the troposphere, derived
from a new data set of recently available observations from the Atmospheric Infrared
Sounder (AIRS, onboard NASA's Aqua satellite), to evaluate the simulations from a
sub-set of the GPCI climate models. We attempt to better understand the variability
(mean, temporal evolution, standard deviation, etc) of humidity in the troposphere
comparing daily averaged output from the models to the satellite data (daily profiles of
RH for the 13 locations along the GPCI cross-section obtained from Level 3 products)
for the season JJA of 2003. To facilitate comparisons with AIRS observations, we take
into account only those simulated profiles with total cloud cover less than 70%. The
AIRS instrument (~2400 channels) suite is a nadir scanning sounder with combined
infrared and microwave retrievals. Aqua is in a sun-synchronous polar orbit, with an
equatorial crossing at ~1330 and ~0130 local time.

Finally, we take a glimpse at preliminary results of CloudSat and Calipso cloud
occurence (derived from 2B-GEOPROF-LIDAR) data for the GPCI cross-section for the
season JJA of 2006. We compare this to climate model simulations of cloud cover.
CloudSat (RADAR measurements) and Calipso (LIDAR measurements) are (along with
Aqua) members of the NASA's A-Train, a constellation of six satellites flying in
formation in close proximity.

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Title: Large-eddy Simulations for the evaluation of the planetary boundary layer
using forcing from a General Circulation Model

Alexandre Catarino, Frédérique Cheruy, Frédéric Hourdin Laboratoire de Météorologie
Dynamique du C.N.R.S.

Poster nr. 21: Tuesday June 3

A common approach to analyze and eventually improve PBL parameterizations of a
GCM relies on the comparison between single column models and large-eddy
simulations, where both models simulate a distinguished case often based on field
observation. This method allows a large number of diagnostics that help to analyze
clearly the PBL features which are aimed to represent, since LES add information that
observations cannot produce. On a new approach, aiming to test the parameterization
behavior within a 3D GCM, the LES is forced by the GCM.
The goal is to maintain all the large scale and surface boundary conditions as similar as
possible on both LES and a GCM grid-box and doing so, the turbulence resolved by
LES can be directly compared with parameterized turbulence and finally several
diagnostics can be applied.
The results of this technique will be applied in the GCPI framework to evaluate the
improvements concerning the representation of PBL clouds at the tropics by the new
mass-flux parameterization of the PBL (Rio & Hourdin, 2007 JAS) recently introduced
on LMDZ (Hourdin et al, 2006 Clim. Dyn.)

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Cross-tropopause transport by convective overshoots in the Tropics

J.-P. Chaboureau, P. J. Mascart, and J. Duron Laboratoire d’Aerologie,
University of Toulouse and CNRS

Poster nr. 22: Tuesday June 3

The increase in the stratospheric water vapor is explained partly by
the troposphere stratosphere exchanges in the tropics. However the
mechanisms of exchange remain much discussed between slow transport by
radiative forcing from the base of the layer of tropical transition
(TTL) and fast convective transport directly to the lower stratosphere.
The recent observations of particles and water vapour measured in the
TTL and nearby the convective systems in Brazil and in Africa can be
explained by transport through convection overshoots only. In support
with these observations, the mesoscale models are a powerful means of
interpretation whose contribution for the study of troposphere
stratosphere exchanges will be re-examined. In a first numerical study
combining in an original way hectometric resolution and real
meteorological conditions, the role of the convection as elevator for
stratosphere was shown. (Chaboureau et al. ACP 2007). The case is
statistics show the increase in vertical velocity with the plume size.
The convection moistens the free troposphere with time, leading to a
decrease in entrainment and an increase in the overshoot efficiency up
to the lower stratosphere. The convection penetrating the stratosphere
will be further demonstrated for an African squall line. The limits
and the consequences on a global scale of the results from these case
studies will be discussed.

Development of a cumulus parameterization with environment-dependent lateral
entrainment rate. Elia

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Development of a cumulus parameterization with environment-dependent lateral
entrainment rate.

M. Chikira, Japan Agency for Marine-Earth Sc. and Technology, Japan

Poster nr. 23: Tuesday June 3

Abstract:
A new cumulus parameterization is developed which has the following features. (1)The
new scheme is based on plume-entraining model. (2)Lateral entrainment rate varies
vertically depending on buoyancy and vertical velocity of cloud air parcel. The formulation is
based on a hypothesis proposed by Grant and Brown (1999) that some fraction of buoyancy-
generated energy is reduced by entrainment. (3)Updraft ensemble is spectrally represented
following the spirit of Arakawa-Schubert scheme. The different updraft types are generated
by different updraft velocities at cloud base assuming that updraft velocity is distributed in a
certain range at cloud base through different strength of thermals, gravity waves and so on.
(4)Cloud base mass flux is determined by the same method as the prognostic Arakawa-
Schubert scheme.
This scheme can reproduce a general feature known through results of cloud resolving
models (CRMs) and large eddy simulations that entrainment rate tends to be large near both
cloud base and top. Vertical profile of entrainment rate largely depends on temperature and
moisture profiles. Especially, entrainment rate is enlarged under the condition of dry ambient
air through a chain of feedbacks, which finally leads to supression of deep convection
consistent with observations and results of CRMs.
A general circulation model (GCM) result using this scheme improves several problems
which many GCMs have been suffering from. (1)Equatorial moist Kelvin waves and Madden
Julian Oscillation-like waves are represented without any empirical triggering schemes,
suggesting that equatorial waves are controlled by entrainment. (2)A bias of precipitation
coming from double ITCZ disappears in the eastern Pacific, which leads to improved spacial
and seasonal variation of precipitation there. (3)SPCZ is well represented. (4)Population of
shallow and middle clouds is increased along with decreased population of deep convection.

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J. N. S. Cole, H. W. Barker, N. G. Loeb, K. von Salzen

Solar radiative fluxes as a function of cloud properties: A comparison between the
CCCma AGCM4 and CERES

Poster nr. 25: Tuesday June 3

Comparisons between radiative fluxes observed by satellite-based instruments and
simulated in global climate models (GCMs) are affected by the geometric and optical
properties of clouds, which can make it difficult to unravel the source of biases within
the GCM. To aid in the determination of the source of biases in GCM, observed and
simulated daily-mean solar radiative fluxes are stratified as a function of their cloud-top
exposed to space as well as other cloud properties.

Estimates of daily-mean top of atmosphere solar radiative fluxes were computed using
fluxes from CERES instruments aboard the TERRA and AQUA satellites. Daily-mean
solar fluxes were generated for cloud tops exposed to space that were high (> 440
hPa), mid-level (440 hPa < 680
hPa) and low (> 680 hPa). The fluxes were estimated by using cloud properties along
the satellite track, assuming that the atmospheric state is invariant through the day and
using the albedo dependence on solar zenith angle. Daily-mean cloud properties, such
as cloud optical thickness and cloud amount, were also saved allowing further

Within the Canadian Centre for Climate Modelling and Analysis (CCCma)
AGCM4 diagnostic radiative fluxes were generated by approximating the methodology
used to produce the CERES radiative fluxes. Fields from similarly sized and timed
orbital tracks from AGCM4 were used to generate diagnostic radiative fluxes for cloud-
tops in the same 3 pressure ranges using the Monte Carlo Independent Column
Approximation (McICA). Use of the McICA allows sub-grid scale and mean radiative
fluxes to be computed in a reasonably efficient manner, in particular when compared to
full ICA calculations. Results of the comparison between AGCM4 and the CERES
fluxes will be presented.

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The field programs COPS and GOP 2007: Possibilies for model improvement

S. Crewell1, K. Ebell1 , T. Reinhardt,1 and V. Wulfmeyer2
1
Institute for Geophysics and Meteorology, University of Cologne, Germany
2
Institute of Physics and Meteorology, University of Hohenheim, Germany

Within the German priority program on Quantitative Precipitation Forecast (QPF) two field
programs were designed in order two provide a sophisticated data set for improving QPF. The
General Observation Period (GOP) [Crewell et al., 2008] was performed by optimizing the use of
existing in-situ and remote-sensing instruments with special focus on water cycle variables over
the full year cycle of 2007. The area of interest covered central Europe with increasing focus
towards the Black Forest where the Convective and Orographically-induced Precipitation Study
(COPS) took place from June to August 2007. Thus the GOP includes a variety of precipitation
systems in order to relate the COPS results to a larger spatial scale. For a timely use of the data,
forecasts of the numerical weather prediction models COSMO-EU and COSMO-DE of the
German Meteorological Service were tailored to match the observations and perform model
evaluation in a near real-time environment (http://gop.meteo.uni-koeln.de/). Since COSMO-DE is
run as a lagged-ensemble where new forecasts are started every 3 h it is possible to investigate
systematically model behaviour. First analyses using GPS network data could reveal that the dry
bias evident in daytime RS92 radiosondes leads to drier forecasts when model runs are started at
noon and afternoon compared to those started at other times. Interestingly, the drier model runs
gain moisture with time as can be seen from GPS and nighttime radiosonde observations. The
influence of this effect on cloud and precipitation development is currently under investigation
using ceilometer, radar and satellite data.

In summer 2007 COPS was performed in a region covering southwestern Germany/eastern
France. The overarching goal of this experiment is the improvement of quantitative precipitation
forecasting in low-mountain regions. For this purpose, a unique synergy of in-situ and passive
and active remote sensing systems was operated for a duration of three months in order to capture
the whole chain of processes leading to the development, organization, and decay of precipitation
systems. Observations were provided by densified networks, a transect of so-called supersites, as
well as by airborne and spaceborne platforms. Through international cooperation with British,
French, Dutch, Austrian and Italian colleagues the instrumental program grew substantially
leading in total to nine aircraft operated during the field phase. COPS itself was endorsed as
Research and Development Project (RDP) of the World Weather Research Program (WWRP).

A special highlight was the operation of the Atmospheric Radiation Measurement (ARM)
Program’s Mobile Facility (AMF) from April to December 2007 in the Murg Valley, Black
Forest, which is an integral part of GOP and COPS. The combination of active and passive
remote sensing instruments for various wavelengths offers the unique opportunity to derive the
atmospheric state as complete as possible. In particular, the Integrated Profiling Technique (IPT,
Löhnert et al., 2008) will be used to derive profiles of temperature, humidity and liquid water
content and corresponding error estimates at the AMF and possible also at the supersites Rhine
Valley and Hornisgrinde. The longterm continuous dataset will be used to investigate cloud
vertical structure and to test radiative transfer schemes of atmospheric models.
Crewell, S., M. Mech, T. Reinhardt, C. Selbach, H.-D. Betz, E. Brocard, G. Dick, E. O’Connor, J.
Fischer, T. Hanisch, T. Hauf, A. Hünerbein, L. Delobbe, A. Mathes, G. Peters, H. Wernli, M.
Wiegner and V. Wulfmeyer, 2008: General Observation Period 2007: Concept and first results.
Meteorol. Z., submitted.

Löhnert, U., S. Crewell, O. Krasnov, E. O’Connor, H. Russchenberg, 2008: Advances in
continuously profiling the thermodynamic state of the boundary layer: Integration of
measurements and methods. Journal of Atmospheric and Oceanic Technology, DOI:
10.1175/2007JTECHA961.1

Wulfmeyer, V., A. Behrendt, H.-S. Bauer, C. Kottmeier, U. Corsmeier, G. Adrian, A. Blyth, G.
Craig, U. Schumann, M. Hagen, S. Crewell, P. Di Girolamo, C. Flamant, M. Miller, A. Montani,
S. Mobbs, E. Richard, M. Rotach, M. Arpagaus, H. Russchenberg, P. Schlussel, M. Koenig, V.
Gartner, R. Steinacker, M. Dorninger, D.D. Turner, T. Weckwerth, A. Hense, and C. Simmer,
2008: The convective and orographically-induced precipitation study: A research and
development project of the World Weather Research Program for improving quantitative
precipitation forecasting in low-mountain regions. Bull. Amer. Meteor. Soc., accepted.
The response of deep convective clouds to aerosol in a range of environments

Z. Cui, S. Davies, K. S. Carslaw, A. M. Blyth

Institute for Climate and Atmospheric Science
School of Earth and Environment
University of Leeds, UK

Poster nr. 27: Tuesday June 3

Deep convective clouds play an important role in the transfer of heat, moisture, trace
gases and aerosols from the boundary layer to the upper troposphere. The interaction
between atmospheric aerosols and the microphysics of mixed-phase convective clouds
are not well understood. We have used a 2-D, axisymmetric, non-hydrostatic, bin-
resolved cloud model to examine the impact of aerosol changes on the development of
mixed-phase convective clouds. We have simulated convective clouds from four
different sites (three continental and one tropical marine) with a wide range of realistic
aerosol loadings. We have also investigated whether the responses of deep continental
convective clouds to changes in aerosol are sensitive to the initial thermodynamic
conditions. In continental clouds, the accumulated precipitation and peak precipitation
intensity decrease with increasing aerosol caused by a reduction in immersion freezing
and subsequent riming rates with smaller droplets. In contrast, accumulated
precipitation increases with increasing aerosol in tropical marine clouds and the
intensity increases up to droplet concentrations at cloud base of ~400 cm-3, then
decreases. These changes are driven by a transition from warm to mixed-phase rain
with increasing aerosol. We have compared the changes in cloud properties caused by
changes in thermodynamics with those due to aerosol. In the continental environment,
the response to changes in thermodynamics tend to be larger than those caused by
large changes in aerosol, and the thermodynamic contrast between the tropical marine
region and the continental regions has a much larger influence on precipitation intensity
and accumulated rain than any of the changes in aerosol we imposed. However, the
response of clouds in the tropical marine environment to changes in aerosol and
thermodynamics are comparable. In general, the sensitivity to aerosol of accumulated
precipitation, peak precipitation rate and peak ice mass tends to be greater in the less
vigorous clouds. Our study suggests that the response of deep convective clouds to
aerosol will be an important contribution to the spatial and temporal variability in cloud
microphysics and precipitation.

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Boundary layer characteristics of the trade wind layer during RICO derived from

Jennifer Davison, Robert M. Rauber and Larry Di Girolamo
Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign

Poster nr. 28: Tuesday June 3

The Rain In Cumulus over the Ocean (RICO) Experiment was designed to examine the
tradewind environment and small cumuli across a broad range of scales, from
microphysical, addressing questions such as precipitation initiation, to mesoscale,
such questions, good environmental characterization of the trade wind layer is vital.
Sets of dropsondes launched from the NCAR C-130 revealed a high degree of spatial
and temporal moisture inhomogeneity – standard deviations of relative humidity of the
order of 10% were common across a single set of ~6 dropsondes launched within ~30
minutes around a circle of ~60 km in diameter. This indicates that soundings alone are
insufficient to characterize the tradewind environment.

Given the high degree of moisture variability suggested by the dropsondes, we
developed an alternate approach to characterize the trade wind environment by making
use of S-Band radar Bragg scattering within the clear air tradewind environment. Two
common clear-air features were observed during RICO: 1) roll circulations, which often
dominate the lowest kilometer, and 2) layers with varying moisture properties extending
to the top of the boundary layer. Using Fourier and wavelet techniques, we are
quantitatively analyzing the entire RICO radar data set to determine the spatial and
temporal coherence and variability of these two features. The goal is two-fold: first, we
want to be able to provide a more descriptive context for any individual cases to be
examined; second, we wish to develop an overall sense of the “true” state of the
tradewind environment through statistical analyses of these features. Fourier-based
techniques are being used to examine the roll circulations. Aspects examined include
wavelength, vertical extent, frequency of occurrence, and interactions with clouds.
Wavelets are being used to examine the layered structure of the environment. Aspects
examined include heights of the boundary layer and the mixed layer tops; as well as
number, lifetime, and depth of transient layers and the subsequent transition layers
between them.

Jennifer Davison
Department of Atmospheric Sciences
University of Illinois at Urbana- Champaign
105 S. Gregory St.
Urbana, IL 61801
E: jdavison@atmos.uiuc.edu

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Passive tracer studies of shallow convection

Jordan Dawe and Philip Austin,

Earth and Ocean Sciences, UBC,

Fleur Couvreux and Caterine Rio, Meteo France, Toulouse, France

Poster nr. 29: Tuesday June 3

Large eddy simulations of an equilibrium trade cumulus cloud field are
used to investigate surface layer/cloud layer coupling for a range of
cloud sizes. We distinguish between small clouds, with life cycles
characterized by a single maximum in the cloud base mass flux, and
larger clouds having similar sub-cloud perturbations in energy,
moisture and vertical velocity but greater horizontal extents and
multiple mass flux "pulses". Using passive tracers from three
sub-cloud layers we look at the source of the cloud base air, the time
history of CAPE and convective inhibition in the pulsating clouds as
well as the vertical and horizontal extent of the sub-cloud region
that feeds the convection. We also compare direct calculations of the
entrainment and detrainment rates to entrainment rates calculated from
a spectrum of entraining plumes, and to the "critical entrainment
rate" needed to activate cloud droplet growth in parameterizations of
aerosol activation (Barahona and Nenes, JGR, 2007)

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Emerging Observations Aerosol-Cloud Processes from the Field Campaigns to
Inform Cloud Models

Manvendra Dubey and Claudio Mazzoleni
dubey@lanl.gov
Los Alamos National Laboratory, Los Alamos NM 87544

Poster nr. 30: Tuesday June 3

We will discuss results from recent field observations* of aerosol effects on clouds and
of cloud processing on aerosols. We will focus on in situ measurements of aerosol
absorption and scattering made using a photoacoustic instrument. The following three
case studies will be highlighted

1. We observed a strongly absorbing aerosol plume within a marine stratus cloud
deck made in N. California with the CIRPAS Twin Otter during the Marine
Stratus Experiment in the summer of 2005. Our analysis shows that black
carbon, when mixed with soot can be effectively scavenged by cloud drops. This
can alter cloud reflectivity, and is important to be considered in cloud models.
2. We observed the effects of cumulus clouds on aerosol properties in the Houston
and Oklahoma, in the Gulf of Mexico Atmospheric Composition and Climate
Study (GoMACCS-2006) and Cumulus Humilis Aerosol Processing Study
(CHAPS-2007) respectively. We find that clouds processed aerosols have
smaller single scatter albedo, which could result from selective scavenging of
scattering aerosols and/or reducing the size of the aerosols. We also show
examples selective scavenging of sulfate by clouds and its dependence on cloud
water.
3. We also plan to report findings on Arctic mixed phase and ice clouds to be made
during April 2008 during the Indirect and Semi-Direct Aerosol Campaign.

Our hope is to facilitate a regular dialogue amongst the field measurements and cloud
modeling community to improve climate models.

*US DOE’s ARM and ASP programs have supported these campaigns

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Analysis of changes in the cloud physical properties of deep convection and surrounding regions

Zachary A. Eitzen, Kuan-Man Xu, and Takmeng Wong

This study uses Single Scanner Footprint (SSF) data from the Clouds and the Earth’s Radiant
Energy System (CERES) instrument on the Tropical Rainfall Measuring Mission (TRMM) space-
craft between January and August 1998. Deep convective cloud objects are identiﬁed for contigu-
ous regions of satellite footprints that fulﬁll the deep convective (DC) criteria (i.e., footprints that
are overcast and have cloud optical depths >10 and cloud top heights >10 km). Previous studies
with this dataset have examined the cloud physical and radiative properties of the cloud objects
themselves; this study also examines the cloud physical and radiative properties of the neighbor-
hoods that the cloud objects lie within. The neighborhood of each cloud object is deﬁned by a box
that extends east-west from the maximum to minimum longitude of the object and extends north-
south from the maximum to minimum latitude of the object. Most of the footprints in these neigh-
borhoods are overcast, but many of these footprints are too optically thin or have cloud top heights
that are too low to ﬁt the deep convective criteria. The histograms of DC and non-DC cloud phys-
ical and radiative properties are further analyzed according to the size of the underlying cloud
object. As the size of the cloud objects increase, the proportion of the cloud object neighborhood
that has DC footprints also increases. For larger deep convective cloud objects, the DC footprints
tend to have higher albedos and cloud top heights, and lower values of outgoing longwave radia-
tion (OLR). The non-DC distributions of albedo are nearly constant with size, while the non-DC
distributions of cloud top height and OLR are slightly shifted towards higher and lower values
with increasing size, respectively. The data presented in this study are useful for understanding the
deep convective cloud feedbacks in the tropics and for comparison with model simulations.
Deep convective clouds as a source of mid-tropospheric aerosols

Annica M.L. Ekman1), Anders Engström1), Radovan Krejci 1), Chien Wang2)
1)
Department of Meteorology, Stockholm University, Sweden
2)
Department of Earth, Atmospheric and Planetary Sciences, MIT, USA

Poster nr. 32: Tuesday June 3

High concentrations (up to 550 1/cm3 STP) of aerosols in the accumulation mode (>
120 nm) were observed by aircraft above 7.5 km altitude around the dynamically active
regions of several deep convective clouds during the INDOEX campaign. Using a 3-D
cloud-resolving model including explicit aerosol physics and chemistry, we find that
significant evaporation of hydrometeors due to strong updrafts and exchange with
ambient air occurs at the boundaries and within the cloud tower. Assuming that each
evaporated hydrometeor release an accumulation mode aerosol, an increase in the
aerosol concentration by up to 600 1/cm3 STP is found at altitudes between 6 and 10
km. The evaporation and release of aerosols occur as the cloud develops, suggesting
that deep convective clouds are an important source of mid-tropospheric aerosols
during the active lifetime of the cloud. This source affects cloud dynamics and
precipitation processes and may also impact on long-range free tropospheric aerosol
transport.

.

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IWP discrepancies between IPCC climate models.

Salamon Eliasson, Lulea University of Technology, Sweden.

Poster nr. 33: Tuesday June 3

Global Climate Models (GCMs) presented in the recently released IPCC AR 4 report show
large discrepancies in their Ice Water Path (IWP) products.
Spatial distributions of modeled IWP are compared to long satellite data sets such as ISCCP
(1983-2006) and Patmos-X (1981-2007).
The spread in IWP values is large, impacting the radiation and hydrological cycle of the
models.
The comparison also shows in which geographical regions they particularly disagree with the
satellite data.
The aim of this particular study is to highlight and present these discrepancies. The primary
objective of the project is to provide data of IWP
that may help to reduce the uncertainty in the representation of ice clouds in the current
generation of GCMs.

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Zhe Feng, Xiquan Dong, Baike Xi
University of North Dakota
Email: zhe.feng@und.edu

Poster nr. 34: Tuesday June 3

A long-term surface merged dataset has been developed using both ARM cloud radar and
WSR-88D precipitation radar observations during the period of 1999-2001 for studying deep
convective systems (DCS) over mid-latitudes. This merged dataset serves as a ground-truth
to evaluate NASA GISS Single Column Model (SCM) simulations and its convective
parameterization. A total of 105 DCS cases during this study period have been selected from
the observations and compared with the currently available SCM simulations. Preliminary
comparison has revealed that SCM successfully simulated 83% of the cases while missing
the other 17%. The SCM simulated convective cloud bulk properties such as cloud fraction,
microphysical/optical properties are also evaluated using the merged dataset. The goal of
this project is to better understand cloud and precipitation produced through convection and
to improve global climate model prediction in the future.

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Simulation of the diurnal cycle of precipitation over Western Amazon in a
CPTEC climate model

SILVIO N. FIGUEROA1, HENRIQUE J. BARBOSA1, PEDRO L. SILVA DIAS2, ENIO P.
SOUZA1 AND JOSE P. BONATTI1
1
Center for Weather Forecasting and Climate Studies-CPTEC, National Institute for Space
Research-INPE , Cachoeira Paulista, São Paulo, Brazil
2
Department of Atmospheric Sciences, Institute of Astronomy and Geophysics, University of Säo
Paulo, Säo Paulo, Brazil

Poster nr. 35: Tuesday June 3

ABSTRACT

The diurnal cycle of precipitation plays an important role in determining seasonal
climate through modulations of surface fluxes of energy and moisture. Many
researchers have found that the convective scheme employed in the model is the most
crucial to capture the diurnal cycle of convection. In order to evaluate the performance
of atmosphere CPTEC climate model (AGCM) to simulate the diurnal cycle of
precipitation during the transition of the dry to wet season over Western Amazon in
2002, a set of ensemble experiments were performed with the traditional Tiedke
shallow (TIED) and Kuo deep (KUO) cumulus parameterization schemes as the
control, and two experiments with the Relaxed Arakawa-Schubert (RAS) and Grell
ensemble schemes. The AGCM results are compared with the Tropical Rainfall
Measurement Mission (TRMM, 3B42RT) satellite data. It is found that the diurnal cycle
of precipitation in the operational climate model produces maximum values in the
afternoon 1400 LT (18 UTC) while the TRMM data shows the maximum precipitation
around 1700 LT (21 UTC). The Grell scheme produce maximum values at 14 LT similar
to the control experiment, however more intense. The RAS produces the maximum
precipitation in the morning around 11 LT (15 UTC). These results suggest that
apparently the TIED parameterization does not realistically take into account the
effects of shallow cumulus clouds over land in the model. It is known that over large
areas in the tropics the shallow convection play an important role as source of heat and
moisture in the lower troposphere and that they may interact with the deeper clouds
through the changes in the environmental conditions. A new set of ensemble
experiments, were performed with another shallow convection scheme (mass flux) with
closure based on maximization of thermodynamical efficiency. The combination this
new scheme and Grell ensemble scheme for deep convection delays the maximum
precipitation to the afternoon around 21 UTC.

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EVALUATION OF VERTICAL PROFILES OF CLOUD IN THE ECMWF FORECAST
MODEL

Richard M. Forbes and Maike Ahlgrimm
European Centre for Medium Range Weather Forecasts (ECMWF)

Poster nr. 36: Tuesday June 3

The current CloudSat and CALIPSO missions are providing a wealth of information
on the vertical distribution of cloud and precipitation across the globe and an
unprecedented opportunity to evaluate the representation of clouds in global
atmospheric models. The ECMWF global forecast model is used across a range of
resolutions for different applications from medium-range to seasonal
forecasting, and improving the prediction of the three-dimensional cloud
distribution has benefit not just for cloud cover, but for the impacts on
radiation and the dynamics through diabatic heating and cooling. Model forecasts
simulating the characteristics of the observations are compared with data from
the spaceborne radar and lidar. A number of aspects of the representation of
cloud in the model are evaluated, including occurrence of cloud in different
geographical regions and vertical profiles of cloud fraction and simulated cloud
properties (reflectivity/backscatter). Current deficiencies in the prediction of
cloud will be discussed as well as improvements due to recent changes in the
ECMWF model.

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Preliminary analysis of the ACCESS single column model for the TWP-ICE case

Charmaine Franklin1
Martin Dix1
Christian Jakob2
Greg Roff1

1. Centre for Australian Weather and Climate Research – A partnership between the
Australian Bureau of Meteorology and CSIRO
2. School of Mathematical Sciences, Monash University

Single column model (SCM) simulations using the Australian Community Climate
Earth System Simulator (ACCESS) atmospheric model are presented for the Tropical
Warm Pool International Cloud Experiment (TWP-ICE) case study. The extensive
observations taken during the field campaign give insight into the ability of the model
to simulate tropical cloud systems through the evaluation of the temperature and
moisture fields and the vertical distribution of cloud properties. It is important in
climate simulations to have the correct vertical distribution of clouds because clouds
redistribute energy vertically and this distribution of energy affects both local and
large-scale dynamics. The atmospheric model of ACCESS is the Met Office Unified
Model (UM). The ACCESS SCM produced reasonable representations of the TWP-
ICE cloud fields, with the three different observed cloud regimes captured by the
model, however there are some differences. The model dissipates cloud too soon after
the large mesoscale convective system event and fails to maintain a thick anvil cloud.
The simulation of the break period, during which time the convection was more
coastal and continental in character, results in too much cloud and a prediction of top
of the atmosphere outgoing longwave radiation that is 30% less than that observed. A
new prognostic cloud scheme, PC2, has been developed at the UK Met Office to
overcome some of the problems associated with the tightly constrained cloud fields
that are produced by the diagnostic scheme used in the UM. A comparison between
the diagnostic large-scale cloud scheme in the model and PC2 shows that the new
scheme is able to represent more of the observed variability of cloud properties due to
the increased number of degrees of freedom.

It has been suggested that the inability of many models to simulate realistic
representations of the MJO may be caused by systematic diabatic heating profile
errors. These errors were seen to be the most pronounced during the suppressed and
break periods of the TWP-ICE simulations. Studies have identified the link between
poor simulations of suppressed convection leading to unrealistic simulations of sub-
seasonal variability in tropical convection, including the MJO, and TWP-ICE may
provide a good case to study the model biases and make improvements in the model
cloud and convection parameterisations.
Low-Level Arctic Mixed-Phase Clouds: Ice Formation under Polluted and Pristine
Conditions

Authors: A. M. Fridlind and A. S. Ackerman
GISS, New York USA

Poster nr. 38: Tuesday June 3

Abstract: Three pre-2008 field experiments have provided sufficient data for detailed
modeling case studies of low-level Arctic mixed-phase clouds: the 1989 Beaufort Arctic
Storms Experiment (BASE), the 1998 Surface Heat Budget of the Arctic (SHEBA)
experiment, and the 2004 Mixed-Phase Arctic Cloud Experiment (MPACE). We describe our
rationale for choosing a single case study from each experiment and our methodology in
using a large-eddy simulation (LES) code with size-resolved mixed-phase microphysics to
develop a numerical simulacrum for each case. Overall, we find that scientific understanding
of ice formation processes under moderately supercooled conditions represents so large an
uncertainty that it is not possible to identify a unique "best representation" for any case.
However, arbitrarily choosing one approach to ice formation that works well for each case,
we find evidence that ice formation appears inhibited in polluted clouds, consistent with past
literature. Furthermore, over ice, where representative case study clouds are of low optical
depth, pollution effects on the efficiency of ice formation appear more important to surface
radiative forcing than pollution effects on the liquid phase (e.g., increase in drop number
concentration or liquid water path). Finally, we survey initial results from the early-2008
Indirect and Semi-Direct Aerosol Campaign (ISDAC) field experiment to investigate the
possibility that more than one case study may emerge from the newest data collected in low-
level Arctic mixed-phase clouds.

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Monsoonal Deep Convection During TWP-ICE / ACTIVE: Progress on an Idealized Six-
Day Case Study

Authors: A. M. Fridlind, A. S. Ackerman, J. Petch, C. Jakob, and S. Xie

Poster nr. 39: Tuesday June 3

Abstract: During January and February of 2006, the Tropical Warm Pool \u2013
International Cloud Experiment (TWP-ICE) and Aerosol and Chemical Transport in
Tropical Deep Convection (ACTIVE) field campaigns overlapped near the US
Department of Energy Atmospheric Radiation Measurement (DOE ARM) site in Darwin,
Australia. Here we present progress on developing a six-day model intercomparison
case study based on the 18 \u2013 24 January active monsoon period. The overall
goal of this work is to help develop a joint DOE ARM / GCSS deep convection model
intercomparison. To maximize suitability for large-eddy simulations, single-column
models, and general circulation models, the case study is idealized as marine, using
specified sea surface temperature. In order to initialize and drive simulations
realistically in the tropical tropopause region, the large-scale forcing data set has been
derived with high vertical resolution (10 mb) and is applied in a manner that returns
model state to that of tropical background conditions measured aloft, regardless of
degree of predicted cloud moistening near the tropopause, without nudging the full
domain and consistent with physical processes based on moisture and budget
analyses. Six idealized tracers are considered as candidates to analyze transport to
and from the tropopause region. Example model results obtained with a large-eddy
simulation code are presented, using both parameterized bulk microphysics and size-
resolved mixed-phase microphysics. For simulations with size-resolved microphysics,
aerosol data gathered from two aircraft during the campaign are used to initialize
background aerosol profile characteristics. Finally, we demonstrate comparison of
simulation results with ground-based, in situ, and satellite measurements, including
liquid and ice water path, cloud base and cloud top elevations, precipitation structure
(radar reflectivity), water vapor, cloud top effective radius, anvil ice size distribution,
rain drop size distribution, and surface radiation and heat fluxes.

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A simplified model for understanding the evolution of cirrus cloud

Timothy J Garrett, Clint Schmidt, Stina Sjostrom, Michael A Zulauf, and Steven K
Krueger

University of Utah, Salt Lake City, USA

Poster nr. 40: Tuesday June 3

At its most fundamental level, the evolution of cirrus cloud is a consequence of
interactions of frozen particulate condensate with a radiation field: heating of cloudy air
drives dynamic adjustments between the cloud and surrounding stably stratified air.
The essential aspects of this problem turn out to be surprisingly simple, although not
yet fully described. Suppose a cloud with dimensions that are finite both vertically and
horizontally, and that is floating in a stably stratified environment. Maximum radiative
warming and cooling are found at cloud base and top, respectively, and the heating
rates extend vertically into the cloud interior a distance that is inversely related to the
density of cloud condensate. These temperature perturbations demand adjustment to
the unheated clear-air surroundings. Adjustment mechanisms available to the cloud
include some combination of cloud convective overturning, isentropic adjustment, and
cloud spreading in narrow layers at cloud base and top. We hypothesize that
determining which of these possibilities dominates cirrus evolution can found by
mapping a space of two dimensionless numbers relating cloud dimensions, condensate
density, cloud temperature, and ambient stability. From cloud LES simulations,
spanning two orders of magnitude in condensate density, and three orders of
magnitude in cloud horizontal width, it is shown that a vector in the spreading number''
and convective number'' does in fact lead to accurate predictions of cloud evolution. A
particularly notable result is that, for the first time, predictions are made of the idealized
conditions required for mammatus cloud formation near cloud base. For these
conditions, mammatus clouds are beautifully reproduced in numerical simulations.

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The role of radiative-dynamic feedbacks in amplifying surface warming by arctic
stratus under polluted conditions

Timothy J. Garrett, Melissa M. Maestas and Chuanfeng Zhao

Poster nr. 41: Tuesday June 3

It has recently been shown that aerosol have the capacity to increase low cloud
longwave emissivity in the Arctic. Increased thermal emission from arctic clouds is
interesting because of its potential to augment the rate of seasonal sea-ice melt. Given
pollution aerosol are most abundant in the Arctic during winter and spring, the
seasonality of the warming is in phase with the melting. Of course, aerosol also
indirectly cool the Arctic surface in summer, provided the surface is black, and the sea-
ice or snow has melted. However, measurements at Barrow indicate that, averaged
over the year, the net indirect forcing of the surface is strongly positive. Polluted clouds
emit 10 to 15 W/m2 more longwave radiation than clean clouds. Notably, however,
measurements and model results suggest that the magnitude of the effect appears to
be influenced not only by increased density of droplet absorption cross-sections, but
also by a positive feedback associated with aerosol-cloud-radiation interactions. Using
a LES model, with idealized microphysics, but coupled radiation and dynamics, we
create stratus from a moist boundary layer. What we find is that, in a polluted
environment, aerosol pollution enhances cloud-top radiative cooling in thin stratus by
making cloud thermally more opaque. Then, compared to clean cloud, the higher
cooling makes dynamic motions more vigorous and the stratus layer deepen more
rapidly: effectively the cloud evolution is accelerated. The combined effect of emissivity
perturbations and radiatively induced feedbacks is to substantially amplify the effect of
aerosol pollution on cloudy thermal emission and Arctic surface warming.

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Evaluation of Diurnal Cycle of Convection in a GCM with Satellite Data

Gehlot, Swati and Quaas, Johannes
Max-Planck Institute of Meteorology, Hamburg

Poster nr. 42: Tuesday June 3

Abstract
:
Clouds are one of the most important components of the climate system, regulating the
radiation budget of the earth. In the simulation of the global climate using General Circulation
Models (GCM), cloud feedbacks contribute to a major uncertainty on account of poorly
represented cloud related processes in the model. In particular, the representation of
convection and convective clouds constitutes at the same time a crucial component of
GCMs and a main source of uncertainty. Satellite observations provide the most
comprehensive view of cloud related quantities at a global scale, and are an important data
source for the evaluation of parameterization schemes.

We present here some experiments with ECHAM5 GCM and their comparison with satellite
observations. This study focuses on the diurnal cycle of convection for monsoon months over
two regions in the Indian subcontinent. The first area being over land and the other in the
ocean, the model's capability in producing two distinct behaviors is analyzed. Sensitivity
studies with ECHAM5 are carried out in order to examine the influence of different
parameters of the convection parameterization in
this model. The International Satellite Cloud Climatology Project
(ISCCP) products and data from the MODerate Resolution Imaging Spectroradiometer
(MODIS) instrument are used as verification data.

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" LES Simulations of the RICO case, sensitivity tests to the microphysical scheme
parameters"

Olivier Geoffroy, KNMI , The Netherlands

Poster nr. 43: Tuesday June 3

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Ensuring consistency of operational NWP cloud and precipitation
forecasts at various resolutions.

Luc Gerard, Royal Meteorological Institute of Belgium,
luc.gerard@oma.be

Poster nr. 44: Tuesday June 3

NWP models with resolutions coarser than 1 or 2 km need a parametrisation of deep
convection, in addition to the resolved condensation and microphysical schemes. When
working with two schemes producing clouds and precipitation one must find a way to
combine these without double counting. In addition, commonly used hypotheses in the
deep convection scheme loose their validity when the size of the grid boxes is not
much bigger than the size of convective cells or systems, and when time steps are
short. The scheme proposed by Gerard (2007) tried to address these difficulties in an
experimental version of the Aladin Model. This scheme has been further improved in
the frame of the pre-operational Alaro-0 model, where it works together with a
microphysics implying 4 prognostic condensed phases (cloud ice and droplets, rain,
snow). This microphysical package includes a parametrization of the Bergeron-
Findeisen effect, a statistical sedimentation computation and a pseudo-graupel
diagnostic. Other refinements compared to Aladin are a prognostic pseudo-TKE vertical
turbulent scheme, the use of semi-Lagrangian horizontal diffusion, a refined radiation
scheme. The deep convective updraught parametrisation has a prognostic closure
based on moisture convergence. It detrains condensates which are combined with the
resolved contribution before entering the microphysics. The "moist" parametrisations
are called in cascade, and the expression of the convective closure helps to prevent
double counting. Among the improvements of Gerard's scheme are a revisited
estimation of the condensation in the updraught, the treatment of interactions between
the resolved and subgrid scheme from one time step to the next, the formulation of the
detrainment, the numerical consistency in the computation of condensation and
transport fluxes. An assessment of model results on a same case at different
resolutions (10km to 2km) and with different model options will be presented.
Verification scores will also be shown and some illustrations of model behaviour.

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Simulated and Observed Aerosol Effects on Mid-Latitude Cyclones

Andrew Gettelman-1, Paul Field-2, Hugh Morrison-1, Steve Ghan-3, Cecile Hannay-1
1-National Center for Atmospheric Research, Boulder, CO
2-Met Office, Exeter, UK
3-Pacific Northwest National Laboratory, Richland, WA

Poster nr. 45: Tuesday June 3

Aerosols may alter the structure of clouds by changing the type and number of condensation
and ice nuclei. Much work has analyzed global impacts and effects on marine stratocumulus
clouds. Here we focus on the effects on mid-latitude cyclonic storms, using models, and
attempting to validate models with in-situ observations. We find potentially significant effects
of anthropogenic and natural aerosols on cyclone structure and moisture. We analyze global
simulations from a climate simulation using a 2-moment microphysics scheme for present
day and pre-industrial aerosol loading by compositing cyclones, and find that for present day
(high) aerosol loading, there are changes to particle size, liquid water path, rain rate and
cloud radiative forcing. In addition, we show preliminary evaluations of the model
microphysics and aerosol effects using recent field campaign data from the Pacific Dust
Experiment (PACDEX) over the Pacific to give us more confidence in the model projections
of aerosol effects.

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Microphysical and optical characteristics of mixed-phase clouds in the Arctic

Vincent Giraud1, Jean – François Gayet1, Guillaume Mioche1, Andreas Dörnbrack 2, Guy
Febvre1, Alfons Schwarzenboeck 1 and Andreas Herber3
1
LaMP CNRS UMR 6016, Université Blaise Pascal, Aubière France
2
Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Germany
3
Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany

Poster nr. 46: Tuesday June 3

Airborne observations were carried out in Arctic boundary-layer clouds during the
ASTAR 2007 campaign in Spitsbergen with several flights coordinated with A-Train
overpasses. The object of the presentation is to discuss the microphysical and optical
properties of mixed-phase clouds from both in situ measurements and co-located space
remote sensing observations (CALIPSO, CloudSat, MODIS). The results may serve to
improve model predictions and can be summarized as the following :
The layer clouds are topped by remnant liquid water layer even for cloud top
temperatures down to -25°C. Quasi-adiabatic LWC values are reported near the cloud
top (~ 0.3 g/m3) and the optical properties at cloud top are dominated by water
droplets. The properties of the ice -crystals precipitating control the reflectivity factor
seen by CloudSat even at the cloud top (occurrence of large ice crystals). A very
efficient conversion liquid cloud-water into ice-particles is evidenced with quite large
values of reflectivity factor (15 dbZ) and precipitation rate (0.5 mm/h).

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On the validation of CALIPSO cirrus-properties with in situ and airborne remote
sensing observations during the CIRCLE-2 campaign

Vincent Giraud1, Guillaume Mioche1, Jean – François Gayet1, Alfons Schwarzenboeck 1,
Jaques Pelon2, Artemio Plana-Flattori3 and Andreas Minikin4

1
LaMP CNRS UMR 6016, Université Blaise Pascal, Aubière France
2
Service d’Aéronomie, Université Pierre et Marie Curie, 75252 Paris France
3
CETP-CNRS , Velizy, France
4
Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Germany

Poster nr. 47: Tuesday June 3

The validation of CALIPSO/CLOUDSAT products dedicated to clouds has been
performed within the frame of the PAZI/CIRCLE-2 project from DLR (Institute for Atmospheric
Physics in Oberpfaffenhofen) in May 2007. During this campaign the LaMP operated a
unique combination of cloud in-situ probes on the DLR F20 aircraft including a Polar
Nephelometer, a Cloud Particle Imager (CPI) as well as standard PMS probes (FSSP and 2D-
C) to measure cloud particle properties in terms of scattering characteristics, particle
morphology and size, and in-cloud partitioning of ice and water content. During the CIRCLE-2
campaign, the DLR F20 flights were co-ordinated with the INSU F20 equipped with remote
sensing instrumentation (RALI : combination of cloud radar and 3- lidar, IR radiometer
CLIMAT…) representing an optimum configuration for CALIPSO/CLOUDSAT validation for
cirrus clouds studies.The experimental strategy of the combined observations consisted to
coordinate the flight plans with the CALIPSO/CLOUDSAT overpass, including the overall
objective to validate the retrieved vertical profiles of cloud parameters (backscattering
coefficient, extinction, thermodynamic phase including ice and/or liquid water content,
effective diameter, …). Preliminary results are discussed on the base of a very well
documented case study with the interpretation of modelling exercises.

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Cloud and Precipitation characteristics of trade wind clouds during RICO derived from radar, satellite and
aircraft measurements.

Larry Di Girolamo, Bob Rauber, Eric Snodgrass, and Sagnik Dey
Department of Atmospheric Sciences, Univerisyt of Illinois at Urbana-Champaign

Precipitation characteristics of trade-wind clouds over the Atlantic Ocean near Barbuda are
derived from radar and aircraft data and compared with satellite-observed cloud fields collected during
the Rain In Cumulus over the Ocean (RICO) field campaign. S-Band reflectivity measurements were
converted to rain rates using a Z-R relationship derived from aircraft measurements. The area-averaged
rain rate for the 62 day period, adjusted for evaporation below cloud base, was found to be 2.0 mm day-1.
Daily rain rates varied from 0 to 18 mm day-1 with most days between 0.5 and 5 mm day-1. The area-
averaged rain rate of 2.0 mm day-1 translates to a latent heat flux to the atmosphere of 56 W m-2, which
when compared to the wintertime ocean-surface latent heat flux from this region results in a precipitation
efficiency of clouds in the trade wind layer of 28-35%. A diurnal cycle was observed which exhibited a
steady increase in precipitation between the hours of 8 PM and 6 AM (LT), a rapid decrease after sunrise
and a second smaller maximum in mid-afternoon. The diurnal cycle was still evident, although less
prominent when heavier rainfall events were removed.
Radar data were collocated with data from the Multiangle Imaging SpectroRadiometer (MISR) to
develop relationships between cloud-top height, cloud fraction, 866 nm bidirectional reflectance factor
(BRF) and radar-derived precipitation. The collocation took place at the overpass time of ~10:45 AM
local time, which corresponded to a local minimum in precipitation in the diurnal cycle. These
relationships revealed that between 5.5% - 10.5% of the cloudy area had rain rates > 0.1 mm hr-1, and
between 1.5% - 3.5% of the cloudy area had rain rates > 1 mm hr-1. Cloud-top heights between ~ 3 - 4 km
and BRFs between 0.4 - 1.0 contributed ~ 50% of the total rainfall. For cloudy pixels having detectable
rain, average rain rates increased from ~ 1 mm hr-1 to 4 mm hr-1 as cloud-top heights increased from ~ 1
km to 4 km. Rain rates were closely tied to the type of mesoscale organization, with much of the rainfall
originating from shallow (< 5 km) cumulus clusters shaped as arcs associated with cold pool outflows.
We also reexamine our results published in 2007 on the statistics of the macrophysical properties
of trade wind cumuli over RICO using 15 m resolution ASTER (Advanced Spaceborne Thermal
Emission and Reflection Radiometer) data in order to better facilitate comparisons between observations
and models. In particular, these cloud statistics are now derived over a variety of pixel and domain sizes
commonly used in cloud resolving models. The strong dependence of these cloud statistics on pixel and
domain size highlight the need for caution in using cloud climatologies derived from coarse resolution
satellites for the purpose of evaluating high resolution simulations of clouds, particularly small trade wind
cumuli.
Representation of deep convection sensitivity to mid-troposphere humidity in LMDZ4
GCM.

Author : JY Grandpeix

Laboratoire de Météorologie Dynamique; Université Paris 6; France. (contact
jyg@lmd.jussieu.fr)

Poster nr. 49: Tuesday June 3

It has been emphasized by several authors (e.g. Lin et al, 2006) that many GCMs did not
represent well the sensitivity of deep convection to free troposphere humidity. This problem
has been adressed in recent developments of the LMDZ4 GCM: coupling Emanuel
convective scheme with the PBL thermal plume model of Rio and Hourdin made it possible
to simulate deep convection inhibition by upper PBL-lower troposphere dryness. However,
there is still no representation in LMDZ4 GCM of deep convection inhibition by a dry mid-
troposphere, an important processe for the occurence of cumulus congestus during the
suppressed periods of the MJO.

We propose a method to represent this process within Emanuel convection scheme. The
idea is to find a buoyancy variable in the scheme that correlates well with CRM convection
depth estimation. We selected as key variable an estimate of the buoyancy of the whole
convective cloud (from base to top, including adiabatic and mixed parts) as a function of the
cloud depth. This variable appears to make it possible to discriminate between shallow and
deep convection, as simulated by CRMs in the Derbyshire idealized humidity case.

We present results in 1D and 3D simulations and analyse the impact of this parametrization
modification on the simulation of cumulus congestus over the west Pacific area.

Reference:
JL Lin et al. (2006): Tropical Intraseasonal Variability in 14 IPCC AR4 Climate Models. Part I:
Convective Signals. J. Clim., 2006, 19: 2665-2690.

C Rio and F Hourdin (2007): A thermal plume model for the convective boundary layer :
Representation of cumulus clouds. J. Atmos. Sci. 2007, In press.

S Derbyshire et al. (2004): Sensitivity of moist convection to environmental humidity. QJRMS
(2004), 130, 3055-3079.

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Tropical Convection Characteristics – Comparisons Between Large-Domain Cloud
Resolving Model Simulations and CloudSat Observations

Sue van den Heever, Matt Rogers and Graeme Stephens
Department of Atmospheric Science
Colorado State University, Fort Collins, CO80523

Poster nr. 51: Tuesday June 3

Data from observational platforms provide us with a means for validating the
output from numerical models, while the simulations enhance our understanding of the
processes governing such observations. Utilizing both observational and model output
is thus an effective way to enhance our understanding of tropical convective processes.
The focus of the research presented here is to compare and contrast a number of
statistical characteristics of tropical convection obtained from large-domain cloud
resolving model (CRM) simulations with those determined using CloudSat data.

The CRM simulations have been conducted within a radiative convective
equilibrium (RCE) framework. The RCE framework has been successfully used in a
number of experiments focusing on the feedbacks between radiation, clouds, water
vapor and convection in the tropics. The use of CRMs in such experiments offers a
more self-consistent treatment of convection and related cloud and radiation processes
than is possible in GCMs and provides a valuable tool for examining the feedback
mechanisms considered important in global models. The simulations have been run
using a channel-type grid domain that spanned 9,600 km in the zonal direction and 180
km in the meridional direction, thus covering an area of approximately 1,728,000 km2.
Use of such a grid accommodates three-dimensional divergence motions, as well as
cold pool dynamics and interactions. The simulations were run out for 100 days.

In order to compare the tropical convection statistics with those observed by
CloudSat, the model output will be processed using Quickbeam, a radar simulator
capable of simulating top-down radar reflectivies at a number of microwave
frequencies, including the W-band cloud precipitation radar on CloudSat. QuickBeam
ingests model profiles of pressure, temperature, relative humidity and hydrometeor
mixing ratios produced by the model, and produces profiles of top-down radar
reflectivity, thus facilitating direct comparisons with CloudSat. The reflectivity profiles
account for attenuation of the simulated radar beam, including those from gaseous
absorption by the atmosphere and from the hydrometeors themselves. These simulated
radar profiles will then be used to generate diagrams such as contoured frequency-
altitude diagrams (CFADs), as well as echo-top height – precipitation-top height (ETH-
PTH) diagrams. Similar diagrams will be produced using CloudSat data from the tropics
and compared with the model output. Other statistics that will also be presented and
compared include various characteristics of the trimodal distribution of tropical
convection, latent heating profiles and precipitating versus non-precipitating clouds
characteristics.

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Inhomogeneities of clouds – a new statistical scheme for large-scale models

Stephanie Heidt, Ulrike Lohmann, Peter Spichtinger

Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland

Poster nr. 52: Tuesday June 3

Clouds play a key role in our climate system, since they influence both the radiation
budget as well as the hydrological cycle. Global climate models to simulate the future
climate are limited to a coarse resolution on the order of 100 km horizontal grid space
due to computational costs. Hence, most clouds are not resolved in these models but
must be parameterized. One key issue is the inhomogeneity of clouds: General
circulation models (GCM) use grid mean quantities of cloud properties to calculate
cloud microphysical processes i.e. representing homogeneous layers of clouds. In
nature, however, clouds are inhomogeneous in terms of microphysical and radiative
properties, which must be represented by using subgrid-scale parameterizations. For a
better representation of clouds we propose a new statistical scheme. We are
implementing a sub column algorithm into the ECHAM5 GCM to take a distribution of
values instead of one mean into account. Cloud cover is then distributed over the sub
columns depending on the diagnosed cloud amount and the number of chosen sub
columns. Mass and number concentration of cloud droplets and/or ice crystals are
distributed randomly over the sub columns according to frequency distributions,
obtained from aircraft observations. This procedure introduces inhomogeneities in the
microphysical properties of the clouds, which then affect the cloud processes (e.g. rain
formation). Due to the better representation of cloud inhomogeneities using this
statistical scheme, a more physical treatment of cloud processes and of their radiative
properties can be achieved.

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Probabilistic Evaluations of a Cloud System Resolving Model Using ARM
Observations

Pete Henderson & Robert Pincus,

Poster nr. 53: Tuesday June 3

Evaluations of Cloud System Resolving Models (CSRMs) are usually made using case-
studies which, by definition, sample a narrow range of atmospheric states over short time
periods. Here we demonstrate an alternative, using a 3-year run to sample a wide range of
conditions. The large size of this data set allows us to use probabilistic evaluation techniques
employing the actively-sensed profiles of cloud properties obtained at the Atmospheric
Radiation Measurement (ARM) program's continental mid-latitude site. This approach also
makes direct use of instantaneous observations, thereby avoiding temporal averaging of the
observations.

The CSRM is driven by ARM's observationally constrained forcing data, and modeled
thermodynamic fields are kept close to those observed by nudging them toward the
soundings; snapshots of the modeled cloud and thermodynamic fields are saved hourly. To
compare the model cloud to the observed cloud, we simulate the measurements made by
the ARM's radar and lidar, and use their sensitivities to define cloud occurrence in the model.
The probability of cloud (PoC) within the CSRM is then evaluated against the combined
binary cloud-mask of the radar and lidar, as a function of height, using methods from
ensemble forecast
verification that compare the statistics of subsets sorted by the model forecasts. Techniques
such as reliability diagrams and Brier scores are then used to quantify performance.

Results will be shown for a range of CSRM configurations, from high-resolution (500 m) 3D
and lower-resolution 2D, typical of the CSRM's implementation in the Multiscale Modeling
Framework, including those employing an intermediate prognostic higher-order turbulence
closure (IPHOC).

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Analysis of the Downward Transport in RICO Observations

Thijs Heus, C.J.Freek Pols, Harm J. J. Jonker and Donald H. Lenschow

Poster nr. 54: Tuesday June 3

The existence of the subsiding shell around cumulus clouds has been observed in
aircraft measurements. Recent results from large-eddy simulations (LES) pointed out
that the downward mass flux through the shell compensates a significant fraction of the
upward mass flux through the cloud; this was not observed before, possibly because
these previous studies usually focused on the one-dimensional velocity profile across
the cloud and the shell without considering the shell area versus the cloud area. Since
mass flux is equal to vertical velocity integrated over area, and the shell area is much
larger than the cloud area, the mass flux in the shell has previously been
underestimated. In this study, air-plane measurements from the rain in cumulus over
the ocean
(RICO) field campaign are used to verify this hypothesis. Similar to the LES results, the
in-shell mass flux is found to be significant. However, a few differences could be found
in comparison with the LES results; most of them could be explained by taking the
difference between the 2-dimensional slabs in LES and the 1-dimensional lines from
observations into account.

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The role of cloud-radiative eﬀects for the soil
moisture-precipitation feedback
a
C. Hohenegger, P. Brockhaus and C. Sch¨r
u
Institute for Atmospheric and Climate Science ETH, Z¨rich, Switzerland

The soil moisture-precipitation feedback is of key importance to our climate
system and its sensitivity to climate change. Previous process studies of
the soil moisture-precipitation feedback have used either regional climate
models of relatively coarse horizontal resolution, which cannot explicitly re-
solve some of the involved processes (e.g., convection), or highly simpliﬁed
models (e.g. conceptual boundary layer or recycling models). The latter
studies have isolated a predominantly positive soil moisture-precipitation
feedback. Here, we investigate the soil moisture-precipitation feedback in
cloud-resolving regional climate simulations. We use the regional climate
model CCLM integrated for one full month on a grid of 2.2-km mesh size
spanning the Alpine region. Initial and lateral boundary conditions stem
from a coarser 25-km CCLM integration. Three sensitivity experiments
have been conducted, one control simulation and two integrations with per-
turbed soil moisture initial conditions. The results are compared to a similar
set of simulations performed at 25-km horizontal resolution and using pa-
rameterized convection.
Comparison of the simulated soil moisture precipitation feedback re-
veals signiﬁcant diﬀerences. In opposition to the 25-km integrations, the
cloud-resolving simulations do not sustain a predominantly positive feed-
back. This diﬀerence relates to the sensitivity of the simulated convective
development to cloud-radiative eﬀects. In the cloud-resolving simulations,
the cloud-induced stabilization of the temperature proﬁle overpowers the
positive feedback loop between soil moisture, Bowen ratio, and convective
activity. In particular, the widespread development of shallow convective
clouds over wet soils chokes down the convective development. Over dry
soils, less shallow but deep convective clouds (and thus enhanced precipita-
tion) can form, since rising air can more easily break through the developing
layer of stable air. The 25-km integrations are almost blind to such eﬀects.
This behavior can be tied to the use of a convective parameterization that
has diﬃculties in representing the gradual deepening of convective cells.
Overall our results thus indicate that parameterized convection may mis-
represent some of the fundamental feedbacks of the extratropical climate
system.

1
Implementing a double-moment warm rain microphysics into the WRF
single-moment 6-class scheme

Song-You Hong, Kyo-Sun Sunny Lim, and Jimy Dudhia*

Department of Atmospheric Sciences, Yonsei University, Seoul, Korea
* Mesoscale and Microscale Meteorology Division/National Center for Atmospheric

The WRF-single-moment-6-class (WSM6) microphysics scheme has been one of
the options of microphysical process in the WRF model since August 2004. This
scheme predicts the mixing ratios for water vapor, cloud water, cloud ice, snow, rain,
and graupel. The characteristics of the cold rain process in the WSM6 scheme follow
the revised ice microphysics process (Hong et al., 2004), whereas the warm rain
processes are primarily based on the works of Lin et al. (1983) and the auto conversion
process from Tropoli and Cotton (1980). The daily forecasts at NCAR have shown that
the WSM6 scheme works successfully in predicting mesoscale convective systems, but
it sometimes overestimates the peak intensity and underestimates the areas of anvil
clouds. We attempts to improve such existing deficiencies in the WSM6 scheme by
incorporating the prediction of number concentrations for warm rain species.

This new method uses a large eddy simulation (LES)-based approach
(Khairoutdinov and Kogan 2000) to determine the autoconversion rates and allow for a
more sophisticated coupling between cloud field and number concentrations of warm
species. Double-moment prediction for the warm species in WSM6 scheme will allow
more flexibility of the size distribution enabling the mean diameter to evolve in contrast
to the one-moment scheme. Thus, the new scheme is called as “the WRF Single-
moment 4-class and double-moment 2-class (WSM4D2)” scheme, which is scheduled
to be available in the WRF model in 2008. The inherent differences between the single-
moment and double-moment approaches are investigated by conducting the sensitivity
experiments, which will be shown in the meeting.
Assessing the simulation of the West-African monsoon by global and regional
climate models along a meridional transect: AMMA-CROSS

F. Hourdin (1), F. Guichard(2), F. Favot(2), Musat(1), A. Dell’Aquila (3), H. Galle (4), T.
Losada (5), P. Marquet(2), P. Ruti(3), A. Traore (1) and A. Boone (2)

Affiliations:
(1) LMD,CNRS, IPSL, Paris, France
(2) CNRM-GAME, CNRS & Météo-France, Toulouse, France
(3) ENEA, Roma, Italy
(4) LGGE, Grenoble, France
(5) UCM, Spain

Poster nr. 57: Tuesday June 3

West Africa is characterized by strong meridional surface gradients coupled to specific
atmospheric circulations, such as the African Easterly jet which develops during the
monsoon season. The West African Monsoon (WAM) further exhibits pronounced
seasonal variations, with an abrupt monsoon onset to be compared to a more
progressive latitudinal retreat. The structure and variability of these basic large-scale
features involve various modes of interaction between physical and dynamical
processes occurring at a range of scales.
The objective of the AMMA-CROSS project is (1) to evaluate and (2) to improve the
ability of global and regional models to simulate these basic large-scale WAM features,
down to intra-seasonal scales.
To do so, an intercomparison is carried out over a West-African South-North cross-
section ([10W,10E]), in the same spirit as developed within GPCI (Siebesma et al.
2004, Teixeira et al. 2007). So far, five different models participate to this exercise:
ARPEGE-Climat, ECHAM-4, LMDZ4, the UCLA GCM and MAR.
Simulations are performed with prescribed, seasonally varying SST. Dynamical fields
are evaluated with analyses (ERA40, ECMWF, NCEP and NCEP2). Physical fields are
compared to available observational products, including precipitation estimates (GPCP,
CMAP, CRU, TAMSAT and AGRHYMET), radiative fluxes (ISCCP, CERES, OSI and
LAND-SAF). LSM simulations over WA (ALMIP project) also provide valuable estimates
of surface heat fluxes.
Differences arising from internal variability are found to be much smaller than
differences between models, and between each model and observations. Beyond
significant and varied departures from observations, all simulations display some
intraseasonal and synoptic modes of variability. These results will be discussed for the
two contrasted years 2000 and 2003. Then, the methodology adopted for an advanced
exploitation of the years 2005-2007 - for which valuable AMMA data exist- will be
presented.

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William Ingram, Oxford , UK

Poster nr. 58: Tuesday June 3

Cloud feedback is generally treated as the important uncertainty in climate sensitivity,
yet the range of water vapour feedback between current climate models is only about a
factor of 2 smaller than that of cloud (if one takes account of the cancellation between
conventionally-defined water vapour and lapse rate feedbacks - if not, the range of
water vapour feedback is actually larger). However, far less research is being done on
the water vapour feedback - apparently for lack of useful ways of quantifying it.

It is becoming generally accepted that the conventional breakdown of climate sensitivity
into "water vapour" and "lapse rate" feedbacks is practically useless. We show it is
also formally useless - if anything, a strengthening of the conventional water vapour
feedback, the strongest positive feedback on climate change, tends to reduce climate
sensitivity slightly - & provide a physical explanation.

The conventional breakdown uses specific humidity (SH) as the moisture variable, not
for any physical reason but because it is the conventional moisture variable in GCMs
(for excellent numerical reasons). Using relative humidity (RH) is as easy to implement,
and removes these problems, though at the cost of losing a readily-identifiable overall
water vapour feedback term. However, further gains are possible by changing the
vertical coordinate to temperature. Obviously some complications follow from
temperature not necessarily varying monotonically with height in the troposphere, but
these can be dealt with, and the analysis has been applied to 4 GCMs. Its greatest
promise is perhaps that it expresses most of the non-cloud longwave component of
climate sensitivity as a term which can be estimated from observations. Unfortunately,
assuming this sample to be representative, the uncertainty in the non-cloud longwave
component mostly comes from the other, smaller terms, so there is no strong direct
constraint. Nevertheless, comparing these 4 GCMs, it clearly indicates genuine
physical differences between them, rather than being dominated by differences in the
distribution of the warming as the conventional breakdown is.

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Deep convection over the eastern tropical Pacific

Toshiro Inoue (CCSR/University of Tokyo)

Poster nr. 59: Tuesday June 3

Split window (11 and 12 micron) is effective to classify optically thin cirrus type cloud
and optically thick cumulus type cloud. Lifecycle of deep convection in terms of cloud
type classified by the split window was studied over the eastern tropical Pacific. Hourly
split window image data of GOES-W during Jan, 2001 and Dec, 2001 were used in this
study. Deep convection mostly consists of optically thick cumulus type cloud at earlier
stage, while cirrus-type cloud area increases with time at later stage. Life stage of deep
convection can be classified by computing the percentage of cirrus type cloud within
deep convection.
Coincident TRMM PR observation was used to study the relationship between rainfall
rate and life stage defined by the split window. As is expected, we found the rainfall
rate tends to be larger at the earlier stage of lifecycle. We also studied rainfall rate in
terms of sea surface temperature (SST) and total precipitable water (TPW) estimated
from TRMM TMI. Generally, rainfall rate increases with increase of SST and TPW.
However, we cannot see clear tendency of percentage of convective rainfall (defined by
TRMM PR) in terms of SST and TPW.
Further, we study the anvil expansion in terms of SST and TPW. Our results indicate
the IRIS effect, although not so strong, for the SST range of 26 30C. However, the
anvil expansion increases over the higher SST region of 3032C. Similar tendency is
seen when we use the TPW. The very large TPW ocean area corresponds to the larger
expansion of anvil.

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Francesco Isotta
Institute for atmospheric and climate science Zürich

Poster nr. 60: Tuesday June 3

The task of the study is to improve the parametrisation of shallow cumulus convection
in the ECHAM5, which is a climate version of the ECMWF general circulation model
(GCM).
The actual version of ECHAM5 contains, for the cumulus convection, the mass flux
scheme of Tiedtke, with modification of Nordeng for deep convection. It distinguishes
between deep convection, shallow convection and mid-level convection, but only one
type of convection is allowed in a grid box at a time. Deep and shallow convection are
mainly distinguished by different fractional turbulent entrainment and detrainment rates.
The Tiedtke scheme has some critical aspects. For example it ignores small cumuli and
it is not able to correctly represent the shallow convection, which is clearly
underestimated in the model. This is a central weaknesses since it is well established
that a global model without a good representation of shallow cumuli leads to a
unrealistic results.
A new shallow cumulus convection parametrisation presented by von Salzen and
McFarlane and already used in the Canadian Centre for Climate Modelling and
Analysis GCM has been implemented instead. In the scheme test parcels are lifted from
the boundary layer to find the level of free convection where the parcel becomes
positively buoyant and the level of neutral buoyancy. The parcels are modified by
entrainment and detrainment at the ascending cloud top, where mixing processes
produce horizontal inhomogeneities, and at the lateral boundaries of the cloud. As a
peculiarity the scheme takes a life cycle of the clouds into account.
The cloud base closure condition proposed by Grant and Bretherton in 2001 is
implemented. The parametrisation is only invoked for cloud tops predicted to be below
the ambient freezing level and a life cycle of the cumuli is considered.
We will show first promising results of the performance of the new implemented scheme
in ECHAM5.

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Precipitation and latent heating characteristics of the major
Tropical Western Paciﬁc cloud regimes
Christian Jakob 1 (Monash University) and Courtney Schumacher (Texas A&M)

An objective tropical cloud-regime classiﬁcation based on daytime-averaged cloud top
pressure and optical thickness information from the International Satellite Cloud
Climatology Project (ISCCP) is combined with precipitation and latent heating
characteristics derived from the Tropical Rainfall Measuring Mission (TRMM) Precipitation
Radar (PR). TRMM precipitation information is stratiﬁed into the ISCCP regimes in the
Tropical Western Paciﬁc (TWP), revealing three major precipitation regimes. These are: a
heavy (12 mm/day) precipitation regime dominated by stratiform precipitation and top-
heavy latent heating, a regime with moderate (5 mm/day) precipitation amounts mostly
convective in nature with more mid-level latent heating and a low (2 mm/day) precipitation
regime with a relatively large rain contribution from shallow convection compared to the
other regimes. While three of the ISCCP cloud regimes are linked to the more convective,
moderate precipitation regime, only one of the cloud regimes is associated with the more
stratiform, top-heavy latent heating regime. This opens avenues for the further study of this
dynamically important tropical weather state.

In terms of the TWP, precipitation and latent heating are dominated by the relatively
infrequent (15 %) occurrence of the strongly precipitating, top-heavy latent heating state
and by the frequent (> 30 %) occurrence of one of the more moderately precipitating,
convective states. The low precipitation/shallow cumulus regime occurs often (i.e., 25 % of
the time), but does not contribute strongly to the overall precipitation and latent heating.
Each of these regimes also show distinct geographical patterns in the TWP, thus providing
insight on the distribution of convective and stratiform rain across the tropics. The potential
application of the ﬁndings of this work for studying the interaction of convection with the
large-scale tropical circulation will be discussed.

1School of Mathematical Sciences, Monash University VIC3800, Australia,
christian.jakob@sci.monash.edu.au
New views on vertical mass transport by cumulus convection

Harm Jonker, Thijs Heus and Peter Sullivan
Technical University Delft , The Netherlands

Poster nr. 62: Tuesday June 3

We show that the traditional view of transport by shallow cumulus clouds needs important
refinement. On the basis of a straightforward geometrical analysis of Large Eddy Simulation
results of shallow cumulus clouds, we conclude: 1) that the upward mass transport by clouds
is strongly dominated by regions close to the edge of clouds rather than by the core region of
clouds; and 2) that the downward mass transport is dominated by processes just outside the
cloud. The latter finding contradicts the accepted view of a uniformly descending dry
environment. We therefore advocate a refined view which distinguishes between the near-
cloud environment and the distant environment. The near-cloud environment is characterized
by coherent descending motions, whereas the distant environment is rather quiescent and
plays no significant role in vertical transport.

We discuss the relevance of the refined view for two areas: dispersion of atmospheric
compounds in a cumulus field and cloud lateral entrainment. It is predicted that a tracer gas
released in the distant environment will hardly diffuse and may stay their for a very long time.
With regard to lateral entrainment we stress that the air being entrained is near-cloud
environmental air, the properties of which differ significantly from the properties of the distant
environmental air, i.e. the mixed air is preconditioned. One could imagine that cloud-mixing
parameterizations might be improved by taking this effect into account. As a first step to
assess this issue we show the results of an extended version of the Asai and Kashara (1967)
model, in which three layers are incorporated: cloud, near-cloud environment, distant
environment.

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Prediction of cirrus clouds in General Circulation Models

Bernd Kärcher and Ulrike Burkhardt

Poster nr. 63: Tuesday June 3

A statistical cloud scheme for non-convective cirrus formed by homogeneous freezing
of supercooled aerosols is presented. As large-scale cirrus clouds exhibit long-lasting,
metastable thermodynamic states and have long lifetimes, a fully prognostic approach
is developed. The scheme is based on separate probability distribution functions of total
water representing clear-sky and in-cloud conditions. These distributions are based on
{\it in-situ} observations and have few degrees of freedom so that they can be used
forecast and climate models. Predictive equations are derived for horizontal cloud
fraction and mixing ratios of grid-mean water vapour and ice water, in-cloud water
vapour and ice crystal number. The scheme allows
sub- and supersaturations with respect to ice to occur in cloud-free air and inside cirrus,
and produces ice crystal concentrations and sizes in good agreement with
observations, an important prerequisite for an improved treatment of cirrus cloud
radiative properties. Open issues and future research avenues are discussed .

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Probability Distribution Functions of Liquid Water Path Associated with Marine
Low Cloud: Geographical and Temporal Variabilities and Controlling
Meteorological Factors

Hideaki Kawai and Masao Kanamitsu
Scripps Institution of Oceanography
University of California, San Diego

Poster nr. 64: Tuesday June 3

Probability distribution functions (PDFs) of liquid water path of marine low cloud over
the eastern Pacific are obtained using geostationary satellite visible data, the main
purpose being to improve low cloud parameterization for large scale models. The PDFs
are calculated over an area of about 200km x 200km, which corresponds to a typical
climate model grid size. A high time-interval (30 minutes) and high spatial resolution
(1km) of the observation covering large areas provided us with fascinating details of the
PDFs from diurnal to seasonal time scales. A shortcoming of the data is that it is
available only during the daytime. The PDFs along the GPCI (GCSS Pacific Cross-
Section Intercomparison)-line, an east-west line at 20S, and a north-south line at 90W
off Peru, during the year 1999-2001 are analyzed. These areas are characterized by
solid stratocumulus, breakup stratocumulus and shallow convections.
The ECMWF reanalysis is used to identify the large scale meteorological parameters
responsible for changes in the moments of the PDF, which include skewness and
kurtosis. We found that the parameter which estimates the strength of the mixing at the
top of the inversion layer made a large contribution to the character of the PDF.
Moreover, a mathematical form of the PDF was estimated from the observation and
compared with the PDFs conventionally used in PDF-based cloud parameterizations.
This study allowed us to provide a more general form of PDF which varies with large-
scale meteorological parameters. We also estimated the impact of the use of the
observed PDF on the cloud-water to precipitation conversion rate, as well as a rough
estimate of the error generated by the plane parallel homogeneous assumption of cloud

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Arctic cloud, circulation, and sea ice during 2007 and beyond

Jennifer Kay,
Andrew Gettelman
Tristan L'Ecuyer
Graeme Stephens

Poster nr. 65: Tuesday June 3

The loss of summertime Arctic sea ice extent is one of the most visible
manifestations of climate change. Yet understanding, observing, and
modeling the physics of the natural and anthropogenic forcings that are
contributing to sea ice loss remains a daunting task.

Our work examines the connections between observed sea ice changes and
atmospheric circulation and cloud patterns using A-train satellites
(CloudSat, CALIOP, AIRS), the NCEP reanalysis, and ground-based
observations from the Atmospheric Radiation Measurement (ARM) site at
Barrow, Alaska. During the record-breaking 2007 sea ice loss, we have
found that cloud reductions and shortwave radiation increases contributed
to observed sea ice melt and surface ocean warming (Kay et al. (in
press)). Longer-term observations show that the 2007 cloudiness and
circulation pattern are anomalous in the recent past, but are not
unprecedented. Thus, we conclude that in a warmer world with thinner ice,
natural summertime circulation and cloud variability is an increasingly
important control on sea ice extent minima.

We are now assessing if uncharted cloud-ice-circulation feedbacks were
present during the 2007 ice loss. We are also estimating the magnitude of
thermodynamic sea ice forcings during the 2007-2008 re-freeze. Finally,
using NCARs community atmosphere model (CAM), we are evaluating the
representation of atmospheric forcings on sea ice in a state-of-the-art
climate model. In particular, we are using CAM in a data assimilation
facility (DART) to compare model-predicted clouds and radiative fluxes
during 2006 and 2007 with observations from the A-train satellites and the
Barrow ARM site. Our findings are providing new insights into both the
relative importance of thermodynamic and dynamic controls on sea ice loss,
and Arctic cloud-ice-circulation feedbacks.

Corresponding author:
------------------------------
Jennifer E. Kay
NCAR/CGD
PO Box 3000
Boulder, CO 80307-3000
ph: 303.497.1730
fax: 303.497.1324
e-mail: jenkay@ucar.edu
web: http://www.cgd.ucar.edu/cms/jenkay/

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AM Kerr-Munslow, JD Price and F Davies.

UK Met Office Research Unit, Cardington Airfield, Beds., MK42 0SY, UK

Poster nr. 66: Tuesday June 3

Abstract

A comparison of the behaviour and retrievals of three microwave radiometers is
and Radiometer Physics HATPRO. Brightness temperatures within the water vapour
line at 23.8GHz and outside at 31.4 or 30 GHz are compared, as well as retrievals of
water vapour and liquid water paths. Two of the radiometers use neural network
retrievals to estimate these, and the third uses a bi-linear regression made against
independently observed liquid water paths. The radiometers were deployed at the UK
Met Office Research Unit in Bedfordshire, UK, during March and April 2007. During
this period, a variety of conditions were observed including clear skies, fog stratus,
stratocumulus and convective cloudy conditions. The results provide an insight into the
relative accuracies between the instruments and their retrievals.

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A computational study of proposed amelioration of global climate warming by
controlled enhancement of droplet concentrations in marine stratocumulus
clouds

Laura Kettles 1* , Alan Gadian1, John Latham2 and Alan Blyth1
1
School of Earth and Environment, University of Leeds, Leeds, UK
2
MMM Division, NCAR, Boulder, Colorado, USA
*
Corresponding author: l.kettles@see.leeds.ac.uk

Poster nr. 66: Tuesday June 3

Abstract:

Marine stratocumulus clouds are of particular interest with regard to climate change,
due
to their widespread cover (about one third of the oceanic surface) and relatively high
albedos. It has been suggested (Latham, 1990, 2002; Bower et al., 2006) that it may be
possible to ameliorate the effects of global warming by deliberately enhancing the
droplet number concentrations (N) in these marine stratocumuli. This can be done
through the addition of cloud condensation nuclei (CCN) in the form of sea-salt aerosol
derived from the ocean below, which leads to increased cloud albedo (Twomey, 1977)
and longevity (Albrecht, 1989) via the first and second indirect effects. This could
ultimately result in a significant negative radiative forcing and associated cooling of the
Earth's climate.

Results will be presented from a computational study in which droplet concentrations in
marine stratocumuli are enhanced, in order to assess how much global cooling could be
achieved. This involves the use of both a global climate model to investigate changes in
the global radiation balance and a cloud resolving model to examine the sensitivity of
the stratocumulus cloud microphysics.

The global climate model used is HadGAM (the atmospheric component of the Met
Office Unified Model) in which N has been increased in all regions of low-level cloud
(not just marine stratocumuli). The effects on cloud droplet effective radius and liquid
water path will be presented for different values of N, along with computations of the

Details will also be given of how the cloud resolving model, the Met Office Large Eddy
Model, is to be used to examine the microphysical and radiational effects of altering
CCN size and number concentrations in warm stratocumuli.

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Intercomparison of model simulations of mixed-phase clouds observed during the ARM
Mixed-Phase Arctic Cloud Experiment. Part I: Single layer cloud

Stephen A. Klein, 1Lawrence Livermore National Laboratory, Livermore, CA, USA

*Full author list*: Stephen A. Klein1, Renata McCoy1, Hugh Morrison2, Andy Ackerman3, Alexander
Avramov4, Gijs deBoer5, Mingxuan Chen6, Jason Cole7, Anthony DelGenio3, Michael Falk8, Mike
Foster9, Ann Fridlind3, Jean-Christophe Golaz10, Tempei Hashino5, Jerry Harrington4, Corinna
Hoose11, Marat Khairoutdinov12, Vincent Larson8, Xiaohong Liu13, Yali Luo14, Greg
McFarquhar15, Surabi Menon16, Roel Neggers17, Sungsu Park18, Michael Poellot19, Knut von
Salzen20, Jerome M. Schmidt21, Igor Sednev16, Ben Shipway22, Matthew Shupe23, Doug
Spangenberg24, Yogesh Sud25, David Turner5, Dana Veron26, Gregory Walker27, Zhien Wang27,
Audrey Wolf3, Shaocheng Xie1, Kuan-Man Xu24, Fanglin Yang28, and Gong Zhang15

*Author Affiliations*:
1Lawrence Livermore National Laboratory, Livermore, CA, USA
2National Center for Atmospheric Research, Boulder, CO, USA
3NASA Goddard Institute for Space Studies, New York, NY, USA
4The Pennsylvania State University, University Park, PA, USA
6Colorado State University, Fort Collins, CO, USA
8University of Wisconsin \u2013 Milwaukee, Milwaukee, WI, USA
9Rutgers University, New Brunswick, NJ, USA
10NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
11ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland
12State University of New York at Stony Brook, Stony Brook, NY, USA
13Pacific Northwest National Laboratory, Richland, WA, USA
14Chinese Academy of Meteorological Sciences, Beijing, China
15University of Illinois, Urbana, IL, USA
16Lawrence Berkeley National Laboratory, Berkeley, CA, USA
17KNMI, Utrecht, Netherlands
18University of Washington, Seattle, WA, USA
19University of North Dakota, Grand Forks, North Dakota, USA
21Navy Research Laboratory, Monterey, CA, USA
22UK Met Office, Exeter, United Kingdom
23Cooperative Institute for Research in Environmental Sciences, University of Colorado / NOAA,
Boulder, CO, USA
24NASA Langley Research Center, Hampton, VA, USA
25NASA Goddard Space Flight Center, Greenbelt, MD, USA
26University of Delaware, Newark, DE, USA
27University of Wyoming, Laramie, WY, USA
28National Centers for Environmental Prediction, Camp Springs, MD, USA

Poster nr. 68: Tuesday June 3

*Abstract*: Results are presented from an intercomparison of single-column and cloud-resolving
model simulations of a cold-air outbreak mixed-phase stratocumulus cloud observed during the ARM
Mixed-Phase Arctic Cloud Experiment. The observed cloud occurred in a well-mixed boundary layer
with a cloud top temperature of \u201315°C. While the cloud was water dominated, ice precipitation

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appears to have lowered the liquid water path to about 2/3 of the adiabatic value. The simulations,
which were performed by seventeen single-column and nine cloud-resolving models, generally
underestimate the liquid water path with the median single-column and cloud-resolving model liquid
water path a factor of 3 smaller than observed. There is some evidence that the liquid and ice water
paths in models with more sophisticated microphysics are in better agreement with the observed
values, although considerable scatter is also present. While the simulated ice water path is in
general agreement with the observed values, results from a sensitivity study in which models
removed ice microphysics indicate that in many models the interaction between liquid and ice phase
microphysics is responsible for the strong model underestimate of liquid water path. Although no
single factor guarantees a good simulation, these results emphasize the need for care in the model
treatment of mixed-phase microphysics. This case study, which has been well observed from both
aircraft and ground-based remote sensors, could be a benchmark for model simulations of mixed-
phase clouds.

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Single column reanalysis - a new GPCI project?

Martin Köhler ECMWF UK

Poster nr. 69: Tuesday June 3

The GCSS Pacific Cross-Section Intercomparison Project (GPCI) has produced a large
set of GCM model data including a few simulations with qualitatively realist tropical
cloud distributions. Here we explore the potential benefits to run a set of single column
models
(SCMs) and/or cloud resolving models (CRMs) on the 13 GPCI points. For that
purpose SCM forcing data is prepared using the currently running ERA interim
reanalysis for the years 1990, 1998, 2003. Interestingly, this reanalysis matches
qualitatively the intriguing multi-annual variability in tropical cloud cover seen in ISCCP
data. At its best, this proposed SCM-GPCI project could allow for direct model physics
comparison to CRM, ERA and observational data. This approach will be demonstrated
using the latest ECMWF upgrades to stratocumulus, shallow cumulus and deep
convection parameterizations. Special attention could be put to evaluating the model
response to forcing with diurnal to inter-annual time scales.

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Impact of SST on the Moist Processes Simulation in the JMA High-Resolution
Global NWP Model for a Tropical Cyclone

Author: Takuya Komori (Numerical Prediction Division, Japan Meteorological Agency)

Poster nr. 70: Tuesday June 3

Abstract:
Modeling cloud and convection play important roles in global numerical weather
prediction (NWP). This study aims to investigate the forecast performance in moist
processes for tropical cyclones (TCs) and to find future issues to address in the global
NWP model of the Japan Meteorological Agency (JMA).
Under the KAKUSHIN project (funded by the Japanese Ministry of Education, Culture,
Sports, Science and Technology), JMA has been developing a new Global Spectral
Model (GSM) with a high horizontal resolution of about 20km and 60 vertical layers
(hereafter called “20km GSM”). The 20km GSM is utilized to evaluate severe weather
events in future climate and has been operational since November 2007.
It is widely considered that the spatial resolution of NWP models play an important
role especially for forecasting severe weather events such as TCs. Additionally, moist
processes in the NWP models play important roles for TC horizontal and vertical
structure. Accurate TC horizontal and vertical structure, especially in a rapidly
developing stage, can give good indications of global NWP models to verify
effectiveness and find future issues to tackle.
To understand which moist process is more effective in the intensification of TC,
sensitivity experiments were conducted with both simplified and daily analyzed Sea
Surface Temperatures (SST). In the former simplified SST experiment, SST anomalies
at the initial time are assumed to persist during the total forecast period. On the other
hand, the latter analyzed SST with 0.25 degree grid resolution, provided by JMA once a
day in near real time, are called “Merged satellite and in situ data Global Daily Sea
Surface Temperatures (MGDSST)”.
The preliminary results on a Pacific TC case in rapid intensification suggest that the
balance between convective and large-scale rains is important to maintain the TC
structure. Further results of other TC cases, and also the impact of the modifications to
the parameterizations will be evaluated and discussed.

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GCSS Precipitating Shallow Cumulus Case: Comparison to RICO Aircraft
Observations

Peter Bogenschutz, Steven Krueger (University of Utah, Utah. USA)

Poster nr. 72: Tuesday June 3

We compared LES (large eddy simulation) of the GCSS Precipitating Shallow Cumulus
Case based on RICO (Rain in Cumulus over the Ocean) observations to cloud
properties measured by aircraft during one RICO flight. We ran the LES at the standard
resolution (100-m horizontal grid size) as well at higher resolution (20-m and 10-m
horizontal grid sizes) for short periods, and examined the impact of increased
resolution.

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Modeling the impact of entrainment and mixing on droplet spectra

by Steve Krueger, University of Utah
steve.krueger@utah.edu

Poster nr. 73: Tuesday June 3

The EMPM (Explicit Mixing Parcel Model) predicts the evolving in-cloud variability due
to entrainment and finite-rate turbulent mixing using a 1D representation of a rising
cloudy parcel. The 1D formulation allows the model to resolve fine-scale variability
down to the smallest turbulent scales (about 1 mm) in a domain 100 m or larger in
length. The EMPM calculates the growth of thousands of individual cloud droplets
based on each dropletÕs local environment.

Our analyses of EMPM results address two fundamental difficulties that the large-eddy
simulation (LES) approach faces when attempting to represent the effects of
entrainment and mixing on droplet microphysics. One is representing the subgrid-scale
(SGS) variability of subsaturation and its impact on droplet size distribution (DSD)
evolution. Another is accounting for the finite rate of SGS mixing and therefore of
droplet evaporation. EMPM results show that the evolution of the DSD due to a single
isobaric entrainment and mixing event depends on the ratio of the grid size to the
entrained blob size. We have also used the EMPM to quantify the dependence of the
relative humidity time scale on droplet evaporation, turbulent mixing, and droplet
sedimentation time scales. These EMPM results can be used as benchmarks for
evaluating LES models.

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Improving the representation of SGS turbulence and clouds in
coarse-grid CRMs

by Steve Krueger and Pete Bogenschutz

University of Utah
steve.krueger@utah.edu

Poster nr. 72: Tuesday June 3

Large-domain coarse-resolution CRMs (with horizontal grid sizes greater than 1 km) are
increasingly being used in regional and global models to resolve deep precipitating
cumulus convection instead of parameterizing it. However, such CRMs typically do not
adequately represent boundary layer turbulence or shallow boundary layer clouds.
Several approaches have been suggested to improve the representation of subgrid-
scale (SGS) clouds and turbulence, including assumed-PDF methods, SGS plume
models, and even embedding a high resolution but small domain 2D eddy-resolving
model. In each of these methods, there are trade-offs between increasing the resolution
of the host CRM and increasing the complexity of the subgrid-scale model.

The approach we are exploring is the assumed-PDF (probability density function)
method, informally in collaboration with Vince Larson (University of Wisconsin at
Madison). In this approach, the general form of a joint PDF for the SGS fluctuations of
vertical velocity, liquid water potential temperature, and total water is assumed. The
actual PDF is determined by several moments. The moments are estimated by
prognostic and/or diagnostic moment equations. When equations for the second and
third moment are used, this approach is also known as higher-order turbulence closure.

Larson et al. (2002) and Golaz et al. (2002a,b) described and tested a 1D cloudy
boundary layer model based on the assumed-PDF approach that uses a double
Gaussian joint PDF. Is their approach suitable for coarse-grid simulations of deep moist
convection?

Larson and Golaz developed and tested their approach for boundary layer clouds using
large-eddy simulations with domain sizes of 6 km by 6 km. For deep moist convection,
a much larger domain is necessary in order to simulate the mesoscale cloud clusters,
while at the same time, the horizontal grid size must still be appropriate for LES (about
100 m), and the simulation must be 3D (Bryan et al. 2003).

We are using the System for Atmospheric Modeling (SAM; Khairoutdinov and Randall
2003) to conduct several large-domain large-eddy simulations of deep moist
convection. We are analyzing statistics collected during the simulations in order to
determine the optimum combination of CRM resolution and complexity of the SGS
model.

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The Entrainment Interface Layer in a High-Resolution DYCOMS-II Stratocumulus
LES

Steve Krueger, Pete Bogenschutz, and Mike Zulauf
University of Utah
steve.krueger@utah.edu

Poster nr. 73: Tuesday June 3

The results suggest that high-resolution LES (5-m vertical and 6-m horizontal grid
sizes) is able to resolve many aspects of the entrainment process in DYCOMS-II
stratocumulus clouds, including cloud ÒholesÓ. In particular, the LES results agree
with DYCOMS-II aircraft observations that showed the average buoyancy in cloud holes
relative to the surrounding cloudy region is close to zero, even though the average
vertical velocity in the holes is negative (Gerber et al. 2005).

The average size of the cloud holes in the LES (80 m) is much larger than observed (5
m). This indicates that LES with a horizontal grid size of 6 m still does not resolve many
aspects of the entrainment process. By comparing high-resolution results to ones at the
ÒstandardÓ horizontal grid size of 50 m, we identified some impacts of using a 50-m
horizontal grid size. An obvious one is poor resolution of cloud holes. Another is
creation of excess negative buoyancy near cloud top by implicit mixing.

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LES investigation of entrainment near the top of marine Stratocumulus

Marcin J. Kurowski, Wojciech W. Grabowski, Szymon P. Malinowski

Poster nr. 74: Tuesday June 3

Abstract:

Large Eddy Simulations(LES) of Stratocumulus-Topped Boundary Layer
(STBL) were performed in order to study details of entrainment/mixing
process in non precipitating marine Stratocumulus clouds. Setup of the
numerical experiment was based on RF-01 case of DYCOMS-II experiment
widely described in the literature.

In order to characterize intense turbulent, rotational flow we
investigate model-resolved enstrophy within and above STBL. We focus
on the stability of the flow in the cloud-top region with use of local
gradient Richardson number at the surface of maximum static stability
(maximum temperature gradient) and at the surface of material top of
STBL defined as jump of total water under a threshold of 8g/kg.
Despite strong static stability at the cloud top, updrafts impinging
into inversion and diverging under it result in shear strong enough to
produces turbulence, which is demonstrated by values of Ri exceeding
critical one. Resulting turbulent mixing is responsible for
entrainment of the free-tropospheric air. Some of mixed parcels, those
with mixing proportion of wet, cloudy air and dry free-tropospheric
air resulting in negative buoyancy, form “cloud holes” - trenches of
descending cloud-free air surrounding areas of updraft.

Evolution of free-tropospheric air entrained into STBL is later
analyzed with use of passive scalar, introduced after three hours of
simulation (i.e. for a quasi-steady state) above the layer of maximum
stability. We observe that concentration of this scalar (which is an
indicator of fraction of entrained FT air within a mixture) in
downdrafts agrees with the proportion of mixing at the cloud top which
results in buoyancy reversal. Negatively buoyant air, sinking through
dry cloud holes, is wrapped around the edge of cloudy regions and
partially recirculated into the cloud. This results in local increase
of cloud base height around cloud holes. Rest of this negatively buoyant air sinks down
STBL.
Conditional sampling performed 20 min, 1 and 3 hours after
introduction of passive scalar demonstrates the temporal evolution of
entrained free-atmospheric air across STBL.

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Dependence of aerosol-cloud interactions
on environmental conditions

Seoung-Soo Lee and Joyce Penner
University of Michicagan, USA

Poster nr. 75: Tuesday June 3

There has been a significant increase in aerosol concentrations with industrialization.
Aerosols are known to increase cloud albedo (first aerosol indirect effect) and possibly
suppress precipitation and alter cloud lifetimes (second aerosol indirect effect). Aerosol
indirect effects are uncertain; the uncertainty in the radiative forcing associated with
aerosol indirect effects are as large as the radiative forcing associated with the
anthropogenic increase in green house gases. Recent studies show that the aerosol
effects on clouds vary with environmental conditions, thus, the changes in cloud
properties due to increasing aerosols depend on environmental conditions. Most
aerosol studies using GCMs have relied on parameterizations which do not consider
the links between environmental conditions and aerosol effects in a physically realistic
way. This contributes to the uncertainty in the radiative forcing by aerosol indirect
effects. In an effort to reduce these uncertainties, this study aims to examine the
mechanisms leading to the different reactions of clouds to aerosol changes and,
thereby, quantify the relation between aerosol effects and environment using a cloud-
resolving model. The quantified relations will enable us to develop a more realistic
parameterization of aerosol-cloud interactions. This study focuses on low-level
stratiform clouds, which play an important role in the global radiation budget over the
North Atlantic where significant increases of anthropogenic aerosols are observed.
Observed stratiform clouds under a variety of environmental conditions are simulated.
Environmental conditions are classified by five factors: relative humidity and large-scale
vertical velocity at the top of boundary layer, surface sensible and latent heat fluxes,
and CAPE. These are known to control the aerosol effects on low-level stratiform
clouds. The dependence of aerosol effects on each of the five factors is isolated to
establish the relation between each of the factors and aerosol effects. The isolation is
carried out by selecting areas where a factor of interest varies widely whereas the other
factors show negligible variations. The effects of increasing aerosols are examined by
conducting present-day and pre-industrial aerosol simulations for each selected area.

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Physics modifications in Meteo France and IPSL models: results on GCSS 1D
cases

(poster)

M-P Lefebvre1, J-L Dufresne2, J-Y Grandpeix2, J-F Guéremy3, F Hourdin2, P Marquet3,
C Rio2
1 Météo-France/Laboratoire de Météorologie Dynamique, Paris, France
2 Laboratoire de Météorologie Dynamique, Paris, France
3 CNRM/GMGEC/EAC, Toulouse, France

Poster nr. 76: Tuesday June 3

Good representation of shallow convection and boundary layer mixing is one of the
major issues of parameterisations improvement in GCM, because of their key role in
radiative and hydrologic budgets. Physics of climate models Arpege (Meteo
France/CNRM) and LMDz (IPSL/LMD) have been modified since their last participation
to IPCC/AR4 runs.
Concerning Arpege climate model, we’ve passed from a “standard diagnostic” physics
used for AR4 runs to a new prognostic physics, with modifications in the following
schemes: turbulence, microphysics, deep and shallow convection and top layer
entrainment.
Concerning LMDz, AR4 simulations have been done with boundary layer turbulence
represented by Louis/Laval scheme and deep convection with Emanuel scheme. Now,
a new parameterization of convective boundary layer is available using mass flux
scheme taking into account thermal plume (Hourdin & al, 2002) coupled with a cloud
scheme (Bony & al, 2001) and prognostic turbulence scheme developed by Mellor &
Yamada. Thermal plume model have been first developed for a dry boundary layer and
then adapted to cloudy situation adding condensation in the updraught and mixing
between thermal plume and its environment (Rio & al, 2008).
Since the end of 2003, Meteo France and IPSL - in order to improve the
parameterizations of their models- decided to cooperate on a common parameterization
library usable in both models. The first step of this project was to add, in the 1D Arpege
Climate model, the entire LMDz physics so we can choose to run one or the other
physics with the same initial conditions and forcings.
In that environment, we’ll present results from 3 GCSS 1D cases: Bomex (trade wind
cumulus), ARM (continental cumulus with diurnal cycle) and RICO (precipitating
cumulus) and show improvements due to the new physics.

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Temperature scaling of precipitation intensities derived from present-day climate and
its relation with climate change.

Geert Lenderink and Erik van Meijgaard
KNMI, De Bilt, The Netherlands

Poster nr. 77: Tuesday June 3

It is commonly anticipated that changes in precipitation extremes under CO2 warming are
constrained by changes in atmospheric precipitable water amounts. Since global climate
models generally predict only marginal changes in relative humidity, the actual precipitable
water scales with the saturation water vapor content. The latter is governed by the Clausius-
Clapeyron (hereafter CC) relation, implying an increase of approximately +7% per degree
global warming. Indeed, evidence from global climate models exists that changes in daily
precipitation extremes scale closely to the CC-relation. However, it is uncertain how general
this scaling behavior is. Here we show that the dependency of precipitation intensity on
temperature may significantly exceed the CC relation on small time and spatial scales. In
observations of 1-hour precipitation intensities at De Bilt (The Netherlands) two times the CC
relation for daily temperatures above 12 oC is derived from the daily variations. The KNMI
high resolution regional climate model (RACMO2) only reproduces this dependency for the
strongest events occurring at temperatures below 20 oC; otherwise the increase in intensity
with temperature is strongly underestimated. For extreme 1-hour precipitation intensities the
climate response between a control period (1971-2000) and a future period (2071-2100)
also shows an increase exceeding the CC relation by a approximately a factor two in large
parts of Europe. Summarizing, this work shows that 1) the CC relation can be exceeded for
strong short precipitation events, 2) modeled intensities show deficiencies in representing
this dependency, 3) a strong hint that dependencies derived from daily variations are a good
predictor of the climate change response. In this talk I will also briefly discus possible
implications of these results concerning cloud dynamics, parameterization issues, and the
potential of using these precipitation intensity relations as a metric of the quality of climate
models.

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Factors influencing cloud area at the capping inversion for
shallow cumulus clouds

Poster nr. 78: Tuesday June 3

Large-eddy simulations are performed of cumulus clouds over a marine
surface. Aspects of the simulations are varied in order to identify
those parameters that play a role in determining under what
circumstances the cumulus clouds spread out under the capping
inversion into stratocumulus. These properties include the strength
of the surface forcing, which then also affects the strength of the
cumulus mass transport, the strength of the capping inversion, the
moisture content of the free atmosphere, the strength of cloud-top
radiative cooling and whether the clouds are allowed to precipitate.
Tests are also performed to evaluate the sensitivity to model resolution.

As in the ATEX intercomparison, having sufficient resolution at the capping
inversion is found to be important for accurate simulation of any
stratiform cloud that forms there. In addition, though, many of the
properties investigated are also found to play a role in determining
the cloud cover. However, a simple rule emerges from the LES that
delineates nicely the circumstances under which the cumulus clouds
spread into stratocumulus. Single column model tests are used to
investigate the ability of the Met Office Unified Model to reproduce
this sensitivity.

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CLIMATE MODEL EVALUATION USING NEW DATASETS FROM THE CLOUDS
AND THE EARTH’S RADIANT ENERGY SYSTEM (CERES)
Norman G. Loeb, Bruce A. Wielicki, and David R. Doelling
NASA Langley Research Center, Mail Stop 420, Hampton, VA, USA, 23681

Poster nr. 79: Tuesday June 3

There are some in the science community who believe that the response of the climate
system to anthropogenic radiative forcing is unpredictable and we should therefore “call off
the quest”. The key limitation in climate predictability is associated with cloud feedback.
Narrowing the uncertainty in cloud feedback (and therefore climate sensitivity) requires
optimal use of the best available observations to evaluate and improve climate model
processes and constrain climate model simulations over longer time scales.
The Clouds and the Earth’s Radiant Energy System (CERES) is a satellite-based
program that provides global cloud, aerosol and radiative flux observations for improving our
understanding of cloud-aerosol-radiation feedbacks in the Earth’s climate system. CERES is
the successor to the Earth Radiation Budget Experiment (ERBE), which has widely been used
to evaluate climate models both at short time scales (e.g., process studies) and at decadal time
scales. A CERES instrument flew on the TRMM satellite and captured the dramatic 1998 El
Nino, and four other CERES instruments are currently flying aboard the Terra and Aqua
platforms. Plans are underway to fly the remaining copy of CERES on the upcoming NPP
spacecraft (mid-2010 launch date).
Every aspect of CERES represents a significant improvement over ERBE. While both
CERES and ERBE measure broadband radiation, CERES calibration is a factor of 2 better
than ERBE. In order to improve the characterization of clouds and aerosols within a CERES
footprint, we use coincident higher-resolution imager observations (VIRS, MODIS or VIIRS)
to provide a consistent cloud-aerosol-radiation dataset at climate accuracy. Improved
radiative fluxes are obtained by using new CERES-derived Angular Distribution Models
2 more accurate than ERBE overall, but the improvement by cloud type and at high latitudes
can be as high as a factor of 5. Diurnal cycles are explicitly resolved by merging
geostationary satellite observations with CERES and MODIS. Atmospheric state data are
provided from a frozen version of the Global Modeling and Assimilation Office-Data
Assimilation System at the NASA Goddard Space Flight Center. In addition to improving the
at the surface and at several levels in the atmosphere using radiative transfer modeling,
constrained at the TOA by CERES (ERBE was limited to the TOA). In all, CERES uses 11
instruments on 7 spacecraft all integrated to obtain climate accuracy in TOA to surface fluxes.
This presentation will provide an overview of several new CERES datasets of interest
to the climate community (including a new adjusted TOA flux dataset constrained by
estimates of heat storage in the Earth system), show direct comparisons between CERES ad
ERBE, and provide a detailed error analysis of CERES fluxes at various time and space
scales. We discuss how observations can be used to reduce uncertainties in cloud feedback
and climate sensitivity and strongly argue why we should NOT “call off the quest”.

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Global impacts of microphysics in convective clouds on the indirect aerosol
effect

Ulrike Lohmann, ETH, Switzerland

Poster nr. 80: Tuesday June 3

Aerosols affect the climate system by changing cloud characteristics in many ways.
They act as cloud condensation and ice nuclei and may have an influence on the
hydrological cycle. Here we investigate aerosol effects on convective clouds by
extending the double-moment cloud microphysics scheme developed for stratiform
clouds to convective clouds in the
ECHAM5 general circulation
model. This reduces the sensitivity of the liquid water path increase with increasing
aerosol optical depth in better agreement with observations and large-eddy simulation
studies. In simulations in which greenhouse gases and aerosols emissions are
increased since pre-industrial times, accounting for microphysics in convective clouds
results in a geographical distribution of the changes in precipitation that better matches
the observed increase in precipitation. The total anthropogenic aerosol effect on the
top-of-the-atmosphere net radiation since pre- industrial times is slightly reduced from -
1.6 to -1.9 W m−2 when microphysics are only included in stratiform clouds to -1.5
Wm−2 when microphysics are included both in stratiform and convective clouds.

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Multi-Layer Arctic Mixed-Phase Clouds Simulated by a
Cloud-Resolving Model: Comparison with ARM Observations and
Sensitivity Experiments

Yali Luo 1, Kuan-Man Xu 2, Hugh Morrison3, Greg M.
McFarquhar4, Zhien Wang5, and Gong Zhang4

1 State Key Laboratory of Severe Weather, Chinese Academy of
Meteorological Sciences, Beijing, China

2 NASA Langley Research Center, Hampton, VA, USA

3 National Center for Atmospheric Research, Boulder, CO, USA

4 University of Illinois at Urbana-Champaign, Urbana, IL, USA

5 University of Wyoming, Laramie, WY, USA

Poster nr. 81: Tuesday June 3

ABSTRACT

A cloud-resolving model (CRM) is used to simulate the multiple-layer mixed-phase
stratiform (MPS) clouds that occurred during a three-and-a-half day subperiod of the
Department of Energy-Atmospheric Radiation Measurement Program’s Mixed-Phase
Arctic Cloud Experiment (M-PACE) and to examine physical processes responsible for
multi-layer production and evolution. The CRM with a two-moment cloud microphysics
is initialized with concurrent meteorological, aerosol, and ice nucleus measurements
and is driven by time-varying large-scale advective tendencies of temperature and
moisture and surface sensible and latent heat fluxes.

The CRM reproduces the dominant occurrences of the single- and double-layer MPS
clouds as revealed by the M-PACE observations although the simulated first cloud layer
is lower and the second cloud layer is thicker compared to observations. The aircraft
measurements suggest that the CRM qualitatively captures the major characteristics in
the vertical distribution and interperiod variation of liquid water content (LWC), droplet
number concentration, total ice water content (IWC) and ice crystal number
concentration (nis). However, the magnitude of LWC is overestimated and those of IWC
and nis are underestimated. In particular, the simulated nis is one order of magnitude
smaller than the observed.

Sensitivity experiments suggest that both the surface fluxes and large-scale advection
control the formation of the lower cloud layer while the large-scale advection initiates
the formation of the upper cloud layer but the maintenance of multi-layer structures
relies on the longwave (LW) radiative effect. The LW cooling near cloud top produces a
more saturated environment and a stronger dynamical circulation while cloud-base
radiative warming of the upper layer creates the stability gap between the two cloud
layers. Both cloud layers are sensitive to ice-forming nuclei number concentration since
ice-phase microphysics provides a strong sink of cloud liquid water mass.

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A Cloud Resolving Model with an Adaptive Vertical Grid

Roger Marchand and Thomas Ackerman
Joint Institute for the Study of the Atmosphere and Ocean
University of Washington, Seattle, Washington USA

Poster nr. 82: Tuesday June 3

Over the last few years a new type of global climate model (GCM) has emerged in
which a two-dimensional or small three-dimensional cloud-resolving model (CRM) is
embedded into each grid cell of a GCM. This new approach is frequently called a
Multiscale Modeling Framework (MMF), but is also known as a cloud-resolving
convection parameterization or a superparameterization (Grabowski 2001, Randall et
al. 2003).     The embedded CRM removes the need for most of the cloud
parameterizations used in traditional GCMs.             However because of the large
computational burden associated with this approach, CRMs in the MMF have been run
using an undesirably coarse grid. For example, MMF simulations by Khairoutdinov and
Randal (2005), Ovtchinnikov et al. (2006), and Marchand et al (2008) used the System
for Atmospheric Measurements (SAM) Cloud Resolving Model with 24 vertical levels
(on a stretched grid) and with a horizontal resolution of 4 km.

Using the GCSS DYCOMS RF01 and LBA test cases, we show that simulations using
SAM with this 24 level vertical grid perform poorly compared with simulations using
much higher vertical resolution.      In the LBA case, which features the formation of
shallow convective clouds and the transition from shallow to deep precipitating
convection, we find that increasing the vertical grid such that there is 100 m resolution
in the boundary layer (and 50 levels in total) captures the timing and strength of the
transition from shallow to deep convection reasonably well when compared with
simulations using 25 m resolution in the boundary layer (and 375 levels in total).
However in the DYCOMS RF01 case, which features a strong inversion topped
stratocumulus cloud, 100 m vertical resolution is still largely insufficient to maintain the
stratocumulus cloud. However, if one places a few additional vertical levels near the
inversion level (and to a lesser degree near cloud base) the cloud is well captured.
We present results of a simulation for the DYCOM case using a version the SAM model
with an adaptive vertical grid. That is the model is able to add vertical layers where and
when needed. In this simulation, the model determines where additional vertical layers
are needed by examining the ratio of the total water flux contributed by the sub-grid
scale scheme to the total water flux.

Khairoutdinov, M. F., D. A. Randall, and C. DeMott, Simulations of the atmospheric
general circulation using a cloud-resolving model as a super-parameterization of
physical processes, J. Atmos. Sci., 62, 2136-2154, 2005.

Marchand, R. T., Haynes, J. M. Mace, G. Ackerman, T. and Stephens, G. 2008, “A
Comparison of Simulated Cloud Radar Output from the Multiscale Modeling Framework
Global Climate Model with CloudSat Cloud Radar Observations,” submitted JGR special
issue on CloudSat

Mikhail Ovtchinnikov, Thomas P. Ackerman, Roger T. Marchand, and Marat
Khairoutdinov, 2005 “Evaluation of The Multi-Scale Modeling Framework Using Data
from the Atmospheric Radiation Measurement Program,” Journal of Climate, 19 (9):
1716-1729 MAY 1 2006

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An evaluation of the surface radiation budget and cloud cover over North
America for a suite of regional climate models and surrogate observational
datasets

M. Markovic
University of Quebec, Montreal

Poster nr. 83: Tuesday June 3

Downwelling longwave (DLR) and incoming shortwave (ISR) radiation are the 2 main terms
in the surface energy balance that control the evolution of surface temperature and moisture.
Systematic biases in the representation of the surface radiation budget (SRB) can lead to
severe errors in a number of key near surface climate variables (e.g. soil moisture, snow cover
and sea-ice amounts). It is therefore important that climate models accurately simulate these
quantities. Cloud cover is one of the main terms influencing the surface radiation budget,
hence an accurate representation of cloud amounts is a crucial component of an accurate SRB.
In this presentation we evaluate the 2 components of SRB and cloud cover over North
America, as simulated by 3 Regional Climate Models (RCMs).

The models used in this study are: CRCM (The Canadian Regional Climate Model), GEM-
LAM (Regional version of Global Environmental Multiscale Model) and RCA3 (Regional
model of Rossby Centre, Sweden). The observations are derived from six different
NOAA. These sites represent a cross-section of various climate types over North America.

In this work we evaluate DLR and ISR in the RCMs against surface observations for different
cloud cover conditions [e.g. cloud-free, all-sky (i.e. conditions as observed) and overcast]. We
try to link respective model radiation biases with erroneous cloud cover representations.
Analysis of the diurnal and annual cycle of cloud cover is performed for 6 observational
SURFRAD sites as well as for 3 the RCMs.

While surface based radiation observations offer accuracy at high temporal resolution, they do
not allow full evaluation of the simulated SRB and cloud cover across the entire North
America. In order to compare the RCMs over wider geographical domain we first evaluate
ISR, DLR and cloud cover for various possible observational surrogate datasets: ERA40
(ECMWF Reanalysis), NARR (North American Regional Reanalysis, NCEP) and ISCCP
(International Satellite Cloud Climatology Project).

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Impact in the ARPEGE GCM/SCM of the top-PBL entrainment on the representation of the
marine strato-Cumulus

Poster by Pascal Marquet (1) , J.F. Gueremy (1) , S. Malardel (2) , V. Masson (2) , E. Bazile (3) , Y.
Bouteloup (3) , F. Bouyssel (3) , J.M. Piriou (3) , F. Beucher (4) , I. Beau (4) , D. Pollack (4) , L. Manlay (5) , V.
Bourdette (5) .
Météo-France, Toulouse, FRANCE. (1) CNRM/GMGEC ; (2) CNRM/GMME ; (3) CNRM/GMAP ; (4)
ENM/UFR ; (5) Students of ENM.

Poster nr. 84: Tuesday June 3

The GCM used at Météo-France is based on the ARPEGE-IFS code. The standard physics presently
available has been developed in the 80’s and the 90’s. It can be considered as somewhat old-fashioned, with
the convection of Bougeault (1985), a moist diagnostic TKE turbulence of Mellor Yamada (1974 to 1982),
diagnostic precipitations and condensates (Smith 1990), the radiation code of Fouquart and Morcrette (1974
to1989).

A large renewal of the atmospheric physics of the ARPEGE GCM has been initiated during the
EUROCS program (2000-03), with several validations and inter-comparisons in SCM and GCM modes,
also by using the EUROCS (first) Pacific cross-section. These validations have been continued during
the GEWEX (GPCI) Pacific inter-comparisons (Athens, 2005 ; New-York, 2006) and then during the
(AMMA) African Monsoon cross-section inter-comparisons (Dakar, 2005).

The new developments concern almost all parts of the atmospheric physics package.
- Turbulence : test of the moist prognostic TKE scheme (C.B.R. / 2000), with B.L.-1989 mixing lengths
and with the parameterization of Grenier (2002) for the top-PBL vertical entrainment ;
- Precipitations and condensed water : use of the Lopez scheme (2002), with subgrid water given by
the mixed Gaussian and Exponential pdf of Bougeault and Bechtold (1982 / 1995) ;
- Shallow Convection : either the Bechtold (2001) or the Gueremy (2005) schemes, with possible tests
of the new EDKF (Pergault) scheme in the future ;
- Deep Convection : either the Bougeault-Gerard (restricted to Deep by Bazile) or the Gueremy (2005)
schemes, with possible test of the future “3MT” scheme (Piriou).
- Radiation : test of the RRTM IFS code for the LW, with 4 to 6 bands in the SW.

Interesting results have been obtained concerning the representation of the marine Strato-Cumulus,
with an important positive impact of the top-PBL vertical entrainment of Grenier, presented in the New-
York GCSS-GPCI workshop, 2006.

The main drawbacks of the new ARPEGE physics observed in GCM mode and with the Gueremy’s
convections concern : (i) a positive bias in the low level wind in the tropical belt ; (ii) some remaining
imbalance in the energy budget of the atmosphere (-10 W/m2).

In order to finalize this new physics in the next version of the ARPEGE GCM, a new challenge has
been decided for 2008: to realize both Climate and NWP cross-validations of the same new physics,
based on the C.B.R. moist prognostic turbulence, the mixed PDF of Bougeault-Bechtold, the mixing
length of BL89 and the Grenier Top-PBL entrainment, with the precipitations of Lopez, the shallow
convection of Bechtold and with the Deep convection of Bougeault-Gerard-Bazile.

Some results will be presented in the PAN-GCSS meeting at Toulouse, with a special attention paid to
the impact of the top-PBL entrainment on the representation of the marine strato-Cumulus, at least by
using new SCM results of the FIRE case as simulated with MUSC, and possibly with new validations
obtained with updated GCM runs of AMMA or Pacific cross-sections.

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The transition from shallow to deep convection over land: High resolution
simulation and parameterization
João P. A. Martins(1); Soares, P. M. M.(1); Teixeira, J. P.(2); Miranda, P. M. A.(1)

(1)   University of Lisbon, CGUL-IDL, Lisbon, Portugal
(2)   Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

In large-scale models the shallow and deep convection are often represented as separate processes, and
its transition is a difficult issue for the modeling community. Furthermore, it is well known that the
diurnal cycle of tropical precipitation is poorly represented in numerical models, with the precipitation
maximum occurring too early when compared with observations. Recently, different approaches to deal
with those problems have been proposed, and some studies suggest that a unified parameterization for
turbulence and convection is desirable.

An improved knowledge of the processes that govern the transition from shallow to deep convection
can be achieved with high-resolution modeling using Cloud Resolving Models (CRM). Until a couple of
years ago, it was very difficult to explicitly simulate those processes due to the lack of available
computer resources. Khairoutdinov and Randall (2006) used a very-high resolution CRM to explicitly
simulate those mechanisms and showed that a new parameterization would have to be based on a
better statistical representation of the boundary layer heterogeneity. Their simulation setup followed
closely a GCSS WG4 case, which was based on an idealization of observations made during the TRMM-
LBA (Tropical Rainfall Measuring Mission - Large-Scale Biosphere-Atmosphere experiment) in Rondonia,
Brazil, on February 23, 1999. The case considered is a daytime convective development over land, which
starts with the growth of a mixed boundary layer, evolving to shallow convective clouds with a later
transition from shallow to deep precipitating convection.

A combined Eddy-Diffusivity and Mass-Flux (EDMF) approach (Soares et al., 2004; Siebesma et al, 2007)
has been developed in order to unify the boundary-layer turbulence and shallow convection
parameterizations. The present study addresses the feasibility of extending that framework to deep
convection.

Here we present a comparison between the results obtained with a CRM and a Single-Column Model
(SCM). Two sets of simulations were considered: (1) a very-high resolution simulation of shallow
convection and (2) a high resolution simulation of the daytime convection, representing the transition
processes from clear to shallow convection, and then to deep convection. All simulations were
performed using the MesoNH model (Lafore et al., 1996) which works both as a CRM and as a SCM, and
has a version of the EDMF parameterization implemented.
Remote Sensing Observations and Modeling for TWP-ICE

S.A. McFarlane, J.M. Comstock, J. Fan, M. Ovtchinnikov

Poster nr. 86: Tuesday June 3

The Tropical Warm Pool – International Cloud Experiment (TWP-ICE), which took place
in Darwin, Australia in Jan-Feb 2006, produced a comprehensive dataset of soundings,
aircraft observations, and remote sensing observations of tropical convection and
cirrus. For these datasets to be useful for model comparisons and evaluation,
retrievals of cirrus microphysical properties from the ground-based remote sensors are
needed. However, ground-based lidar and radar remote sensors both have difficulty in
fully observing cirrus clouds. Due to sensitivity issues, cloud radar can miss small
crystals at the tops of cirrus or miss thin cirrus altogether and lidar is attenuated by
optically thick cirrus or by liquid clouds below the cirrus. We present cirrus
microphysical properties retrieved using a new combined lidar-radar algorithm. We use
these retrieved cloud properties to calculate radiative heating rates during the TWP-ICE
period. We will compare observations with initial model simulations, including
simulated lidar and radar measurements, for case studies from the TWP-ICE period
using a cloud-resolving model with explicit bin microphysics.

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Brian Medeiros UCLA, USA

Poster nr. 87: Tuesday June 3

Recent work has focused attention on tropical low-level clouds as the source of
divergence in GCM-based estimates of climate change. This study investigates the
distribution and response of simulated clouds in a set of GCM experiments using the
NCAR CAM and GFDL AM, including both realistic geography and idealized aquaplanet
simulations. We emphasize shallow cumulus convection regimes, which have modest
cloud cover but are found over a large fraction of the tropical ocean, and which respond
differently between the GCMs for the same prescribed climate change. Conditional
distributions are derived from the model output to isolate shallow cumulus regimes and
make comparisons with observations of shallow cumulus, including from the RICO field
campaign and the CALIPSO mission. The simulated vertical structure of shallow
cumulus clouds is relatively insensitive to the large-scale conditions among the
simulations from any given model, but differs between models. The NCAR CAM distorts
the vertical structure of shallow convection, with unrealistically large cloud fraction and
unrealistically shallow cloud base. The representation of the structure of shallow
cumulus convection is better captured by the GFDL AM. The vertically-integrated cloud
amount is similar between the GCMs, though, because they apply different cloud
overlap assumptions. The response in cloud and condensate distributions to the climate
change are opposite in the GCMs, and tend to be more coherent in the GFDL AM than
the NCAR CAM. Work is ongoing to identify a basis for testing these divergent
responses using data selected from different environments sampled by the present
climate.

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Title: Properties of the convection scheme in JMA-GSM

Author: Kengo Miyamoto, JMA Tokyo, Japan

Poster nr. 89: Tuesday June 3

Abstract:
The fact has been known for many years that JMA-GSM contains a dry bias in the middle of
the troposphere over the Japanese archipelago in boreal summer. However, we had not
been able to investigate the properties of the bias, even how does the dry bias range
throughout the world, because of lack of reference data. Observations by radiosondes, which
are the only way to observe vertical profiles of specific humidity, exist only in some limited
area on land. Some brand new data sources recently started to provide data. Some of those
data enabled us to investigate the properties of the bias, though only indirectly.
I tried to reveal some properties of the bias, by using the data observed by CloudSAT and
CALIPSO and the data provided by the TIGGE database. The investigation concluded that
the dry bias is probably due to deficiencies in our cumulus convection scheme (an
economical version of the prognostic Arakawa-Schubert scheme). Comparisons of cloud
occurrence between CloudSAT, CALIPSO, and JMA-GSM revealed follows: the deep
convection simulated by JMA-GSM is active at wherever it must be active, and vice versa;
the value of cloud occurrence simulated by JMA-GSM tends to be too small in the middle of
the troposphere where deep convection is active; the height of cloud top simulated by JMA-
GSM is correct except for the Antarctica. Intercomparisons of specific humidity between
three NWP centers (JMA, ECMWF, and UKMO) revealed that the middle of the troposphere
of JMA-GSM is dryer than those of the other two NWP centers where deep convection is
active.
I am going to improve our cumulus convection scheme through comparisons with our cloud
resolving model (JMA-NHM). For the first step, I am currently investigating properties of our
cumulus convection scheme (e.g., vertical profiles of heating and moisten rate).
In the presentation, I briefly introduce our cumulus convection scheme @and show some
results of the comparison of JMA-GSM with CloudSAT, CALIPSO, and other two models
(ECMWF and UKMO). I will show the properties of our cumulus convections scheme and
discuss the cause of the dry bias.

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A new LES code based on a vector-vorticity model
Chin-Hoh Moeng

We developed a new LES code based on Jung-Arakawa’s (2008, MWR, 136, 276–294)
vector-vorticity model. The vector-vorticity model, originally developed as a cloud-resolving
model for deep convection, solves vorticity equations instead of the usual momentum equa-
tions. For the basic dynamical framework, it consists of only two time-rate-of-change equa-
tions for the two horizontal components of vorticity ωx and ωy . The vertical component of
vorticity is solved prognostically only at one selected height (e.g., at the top of the numerical
domain), and is solved at the other heights by vertically integrating the horizontal divergence
of the two other vorticity components, i.e., –(∂ωx /∂x + ∂ωy /∂y).
The velocity ﬁeld is solved as follows: First the vertical velocity w is solved from an elliptic
equation derived from anelastic continuity. The horizontal velocities are then computed
diagnostically by vertical integration of ∂w/∂x + ωy and ∂w/∂y − ωx , respectively, except at
one selected height (e.g., the top of the model domain) where the horizontal velocities are
solved prognostically.
The model ouput thus consists of all three components of vorticity as well as the vorticity
induced velocity ﬁeld. The pressure eﬀect is never explicitly accounted for in the model.
We use the vector-vorticity model as an LES for turbulence simulation. We will show that
it can generate statistics of convective PBLs reasonably well and can be used to investigate
vorticity dynamics in 3D turbulence.

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