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  Scale interactions and organized
convection in the tropical atmosphere

     Project Manager: Steve Woolnough
Organization of tropical convection
• Tropical convection is organized across a
  wide range of scales associated with
  – Individual cloud systems
  – Squall lines and mesoscale convective
  – African Easterly Waves, Tropical Cyclones,
    Equatorial Waves
  – Madden-Julian Oscillation, Monsoon
   Interactions between space and time scales
               of tropical convection

                                       activity      Seasonal Cycle
Diurnal Cycle

                                                  Modulates           Monsoon
                MJO Suppressed                     activity            Onset?
                Upscale                     Upscale
              organisation?               organisation?
  Mesoscale                   Synoptic                        MJO
   systems                     waves
                Modulates                  Modulates
10-100’s km      activity     100’s km      activity      1000’s km                El Nino &
                                                                                Climate Change
    Hours                      Days                           Weeks                 (WCRP)
           MJO in Climate Models

• Lin et al. (J. Clim, 2006) (CGCMs)
  – MJO variance approaches observed value in
    only 2 of 14 models
  – Ratio of eastward to westward variance is too
    small, consistent with lack of coherent
    eastward propagation
  – Variance in 13 of 14 models not associated
    with pronounced spectral peak.
             Multiscale Organization in the MJO
                                         • Eastward propagating envelope
                                           of convection
                                         • Short lived, westward
                                           propagating systems within
                                         • With individual mesoscale cloud
                                           systems embedded within them

from Chen et al. (J. Atmos. Sci, 1996)     from Rickenbach & Rutledge (J. Atmos. Sci, 1998)
     Multiscale Organization in the MJO

• What role do the different scales of organization
  play in the transports of heat, moisture and
  momentum by the convection?
• How are these processes represented within
  conventional parametrization schemes?
  Scientific & Technical Challenges
• How does convection organise itself across a range of
  time and space scales?
• How are energy and momentum transferred?
• Why do preferred structures emerge?
• How can these be represented in global models?
• But we cannot answer these questions using
  observations - so we must use models as pseudo ‘field
• This requires large domains and very high resolution so
  that the energy spectrum is not compromised.
• Needs very significant computational resource, only just
  becoming available.
           Cascade Project
• Natural Environmental Research Council
  (NERC) Funded Consortium Project
  – Walker Institute, University of Reading
  – National Centre for Atmospheric Science
  – University of Leeds
  – University of East Anglia
  – Met Office
• 3½ year project which started on 1st
  October 2007
• Develop modelling framework for large domain (100 longitude
  by 30 latitude), high resolution (1-2 km) simulations.
• Perform numerical case studies of organised convection over
  West Africa and the Indo-Pacific Warm Pool.
• Evaluate these simulations using advanced satellite and in situ
  observations of cloud structures.
• Analyse the simulations in terms of scale-dependent energy
  and momentum budgets.
• Use idealised case studies to explore the links between
  convection and equatorial wave modes.
• Bring this new understanding into the development of new
  representations of tropical convection for global weather and
  climate models.
             Project Structure
WP1: Development of Modelling Tools and Infrastructure

WP2: Scale interactions in African Weather Systems

WP3: Organized Convection over the Indian Ocean and
 West Pacific Warm Pool

WP4: Model Evaluation against Observations

WP5: Synthesis of Results
 Development of Modelling Tools and
• Model Development (Met Office)
  – Met Office Unified Model
     • Build on existing work in the Met Office to develop 1km
       resolution LAM for use as forecasting tool and CRM research
     • Includes options for
        – 3D turbulence scheme
        – 5 phase microphysics scheme
     • Test small domain case studies
• Modelling Infrastructure (Lois Steenman Clark,
  – Optimatization
     • Scalability
     • Performance of I/O
  – Management of TB of data
Simulations of the diurnal cycle and land-sea breezes
        over the Tiwi Islands in the Timor Sea

          Evidence of modelling capability:
Realistic physical-dynamical coupling in 1 km version of the
                       Unified Model
Simulations of the diurnal cycle and land-sea breezes
        over the Tiwi Islands in the Timor Sea

               Evidence of model skill:
         Good agreement with radar observations
     Scale Interactions in African
          Weather Systems
• Diurnal Cycle of Convection (Tony Slingo,
  Walker Institute)
  – What mechanisms control the organization of
    convection by the diurnal cycle over varying land
    surface conditions and forcing regimes typical of
    North Africa?
• MCSs and AEWs (Doug Parker, U of Leeds)
  – What is the role of MCSs, particular those forced by
    the diurnal cycle, in the dynamics of the regional and
    synoptic waves and vortices over Africa?
     Organized Convection in the
       Indo-Pacific Warm Pool
• Scale Interactions in the MJO (Steve
  Woolnough, Walker Institute)
  – How do the vertical heating profiles and momentum
    transports associated with convection influence the
    evolution of the MJO?
• The diurnal cycle and the climate of the Maritime
  Continent (Adrian Matthews, UEA)
  – What role do the diurnal cycle and land-sea breezes
    play in determining the mean climate of the Maritime
Organized Convection in the Warm
• Idealized Simulations of organized convection
  and equatorial waves (Brian Hoskins, Mike
  Blackburn, Walker Institute)
  – How is convection organized by equatorial waves and
    how does it modify the structures predicted by the dry
       Case Study Methodology
• Use the high resolution simulations as pseudo-
  observations to investigate
  – the energy and momentum budgets associated with
    organized convection
  – the interactions between the various scales of
• Compare with low resolution simulations to
  identify weaknesses and missing processes in
  convection parametrization schemes
       Model Evaluation against
       Advanced Observations
                    (Robin Hogan, Walker Institute)

• Use geostationary Satellites to evaluate
  temporal development of organized cloud
• Use CloudSat, CALIPSO, and surface ARM
  sites to evaluate vertical structure of clouds
         Synthesis of Results
                                      (Met Office)
• Review the results from a parametrization
  perspective including
  – role of organized convection
  – Environmental influences on organization
  – Temporal evolution of convection
• Test new parametrization ideas in low resolution
  simulations of case studies
                         Project Timeline
                                                Oct   Apr   Oct   Apr   Oct   Apr   Oct   Apr
                                                ’07   ’08   ’08   ’09   ’09   ’10   ’10   ‘11
Model Development, Porting and Optimization

African Case Studies
• Case Identification and Model Configuration
• Diurnal Cycle
Warm Pool Case Studies
• Case Identification and Model Configuration
• Maritime Continent
• Equatorial Waves
Model Evaluation against Observations

Synthesis of Results

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