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SCOUT-O3
Stratosphere-Climate Links with
Emphasis on the Upper Troposphere
and Lower Stratosphere
Publishable Executive Summary - Final draft
European Commission
Framework 6 Integrated Project
Thematic Priority 1.1.6.3
505390-GOCE-CT-2004
1 May 2004 to 31 August 2009
Contact
Prof. J.A. Pyle & Dr N.R.P. Harris
European Ozone Research Coordinating Unit
Department of Chemistry
University of Cambridge
Lensfield Road
Cambridge CB2 1EW
United Kingdom
Email: Neil.Harris@ozone-sec.ch.cam.ac.uk
Web: www.ozone-sec.ch.cam.ac.uk
Design
Rebecca Penkett
Marina Tselepi
Neil Harris
Acknowledgements
Many people particiapted in the SCOUT-3 project and they all contributed indirectly to this project summary.
They are too numerous to mention, but we would like to acknowledge their contributions and thank them for
it. Here we thank those who contributed directly to the preparation of this summary, namely,
Alkis Bais, Peter Braesicke, Geir Braathen, Martyn Chipperfield, Thierry Corti, John Crowley, Martin
Dameris, Andreas Engel, Veronika Eyring, AnnMari Fjaeraa, Peter Haynes, Scott Hosking, Jussi Kaurola,
Rigel Kivi, Ulrike Langematz, Robert MacKenzie, Virginie Marecal, Hermann Oelhaf, Yvan Orsolini, Thomas
Peter, Jean-Pierre Pommereau, Thomas Reddmann, Markus Rex, Maria Russo, Cornelius Schiller, Gunther
Seckmeyer, Harjinder Sembhi, Peter Siegmund, Björn-Martin Sinnhuber, Harry Slaper, Gabi Stiller, Bill
Sturges, Mark Weber, Jason Williams, ABC, AEMET, DLR, FZJ and FZK.
ii
Preface
The discovery of the Antarctic ‘ozone hole’, nearly 25 years ago, provided confirmation of a major
environmental issue: chlorine- and bromine-containing compounds, with many industrial and domestic uses,
were implicated in the destruction of stratospheric ozone. This discovery led to the Montreal Protocol,
which has become a model for how scientific understanding can contribute to environmental regulation.
European scientists, funded in a series of national and EU research programmes, responded to the developing
scientific challenges. In particular, coordinated, collaborative action, through a number of EU field campaigns,
showed that ozone was also being depleted in the Arctic, and subsequently described the processes by which
middle latitude decreases in ozone, and impacts on UV, were occurring. One of the major successes of this
period was the development of a coherent European stratospheric science community which continues to
play a major role in international science and international assessment for policy.
Europe has also led the developing science agenda into the area of chemistry/climate interactions as scientists
turn their attention to the evolution of the ozone layer during the coming century. This overarching issue is
the major focus of SCOUT-O3, which has involved laboratory, field measurement and modelling scientists.
Major international initiatives have included field campaigns in the tropics and a leading contribution to
international modelling programmes.
70 institutional partners, and more than 400 scientists, have contributed to the SCOUT-O3 project. Thus
far, over 350 scientific papers have been produced, with many more to follow. SCOUT-O3 results, and
scientists, will play a central role in the upcoming WMO/UNEP assessment on the state of the ozone layer.
The EU contribution of 15M€ provided crucial leverage with more than twice this amount coming from
national funding agencies, emphasising SCOUT-O3’s role in bringing together a pan-European community
of scientists. More importantly, the SCOUT-O3 heritage includes a European science community committed
to excellence through collaboration. These are achievements of which we are very proud.
John Pyle, SCOUT-O3 Coordinator
November 2009
1
2
Table of Contents
SCOUT-O3 Rationale and Approach 4
Laboratory Measurements 6
Observing the Atmosphere 8
Atmospheric Models 10
Coordinated Activity 1: Darwin Campaign 12
Coordinated Activity 2: Understanding Clouds, Aerosols and UV 13
Coordinated Activity 3: SCOUT-O3 / AMMA Campaign 14
Coordinated Activity 4: SPARC / CCMVal 15
Meeting the Objectives 16
Objective 1: Transport Through the Tropical Tropopause Layer (TTL) 18
Objective 2: Clouds in the Tropical Upper Troposphere and Lower Stratosphere 20
Objective 3: Understanding Stratospheric Water Vapour 22
Objective 4: Stratospheric Aerosol Layer 24
Objective 5: Past Surface UV Changes, Variability and Trends 26
Objective 6: Ozone at Mid-Latitudes 28
Objective 7: Polar Ozone in a Changing Atmosphere 30
Objective 8: The Brewer-Dobson Circulation 32
Objective 9: Stratosphere-Troposphere Coupling: Past and Future 34
Objective 10: Predictions of Ozone Recovery on Surface UV 36
The World Avoided by the Montreal Protocol 38
Future Directions for Stratospheric Research 40
Data Policy and Database 41
Dissemination, Outreach and Human Capital 43
List of Organisations involved with SCOUT-O3 46
3
SCOUT-O3: Rationale and Approach
Rationale
The rationale for the SCOUT-O3 project is to provide scientific knowledge for global assessments on ozone
depletion and climate change for the Montreal and Kyoto Protocols. European countries and the European
Union have a responsibility under: the Montreal protocol of the Vienna Convention; the UN Framework
Convention on Climate Change; and the Kyoto Protocol. The Montreal Protocol has successfully reduced
emissions and atmospheric concentrations of chloroflorocarbons (CFCs), which are estimated to return to
their pre-ozone hole concentrations by about 2050. The Kyoto Protocol was the first international measure
to put a restraint on the galloping rise of carbon dioxide (CO2) emissions caused by industialised nations.
However, the ozone layer is unlikely to return to its pre-ozone hole state by 2050 and so the remaining
central question for the Montreal process is: “How and when will ozone and UV radiation recover as CFC
concentrations fall?”. The answer is required in order to provide essential advice to policy makers in Europe
and world-wide.
Such scientific knowledge about the state of the atmosphere and the processes that govern it constitutes the
basis for political negotiations and decisions concerning the phase-out of ozone depleting substances and
greenhouse gases emission limits. SCOUT-O3 has contributed to this knowledge, which is necessary to
formulate a sound environmental protection policy. The improvement of computer models (a central goal
of the project) is necessary for the prediction of future ozone loss. Such predictions have implications for
international policies on the phase-out of ozone depleting substances.
Results from SCOUT-O3 have formed important European input to international assessments, such as the
Intergovernmental Panel on Climate Change (IPCC), whose fourth assessment report came out in 2007.
More direct input was made to the IPCC/TEAP report on ‘Safeguarding the ozone layer and the global
climate system’ in 2005 and to the UNEP/World Meteorolgical Organisation Scientific Assessment of
Ozone Depletion in 2006. SCOUT-O3 and SCOUT-O3 scientists are also making major contributions to its
successor which is due out in 2010.
4
SCOUT-O3: Rationale and Approach
The SCOUT-O3 Approach
The central aim in SCOUT-O3 was to analyse and predict the current status and future evolution of the
ozone layer and surface ultra violet levels with increased confidence. SCOUT-O3 scientists developed and
implemented a science plan which covered the most important component issues. Central to this was the
integration of understanding gained from new and existing measurements using a variety of models operating
on all spatial scales. Doing the job properly requires, for example, knowledge of dramatic individual
thunderstorms extending perhaps 50-100 km for a few hours, as well as the more subtle, hard to define
aspects of the overall atmospheric circulation taking place over the whole globe over many years.
Better understanding of processes in the upper troposphere and lower stratosphere (UTLS) has been
achieved through modelling and data analysis, and studies of the long-term variability in extratropical large
scale transport have been made to improve long-term predictions of mid- and high latitude ozone and ultra
violet. Knowledge about the past and present variability in ultra violet radiation has been improved using
re-evaluated and quality controlled data sets. These have been complemented by focused studies involving
measurements and modelling and used to improve understanding of how clouds and aerosols modify
atmospheric radiation.
Our appreciation of the wide-ranging importance of chemistry/climate feedbacks developed considerably
during the last decade. This is now seen as a crucial component of the ‘earth system’ and one where
further progress is essential for successful prognoses of the future development of the system. SCOUT-
O3 has made a major contribution to global change studies by concentrating on these chemistry/climate
issues. A comprehensive range of scenarios were used in chemistry climate models to provide the basis for
comprehensive studies of the evolution and feedback of the coupled chemistry/climate system.
Lack of knowledge about the tropical stratosphere and upper troposphere, a crucial region when making
predictions, was addressed through tropical field campaigns involving aircraft and balloons which investigated
detailed mechanisms by which air passes from the troposphere to the stratosphere. New fundamental
information about chemical and microphysical processes gained from laboratory studies have been used
in atmospheric models to interpret the measurements of the atmosphere. Understanding of the larger scale
importance is gained through analysis of satellite measurements (e.g. from ENVISAT and CALIPSO),
meteorological analyses and other global fields.
In order to address the central question, 10 scientific objectives were defined which served as a basis for the
science plan. The significant progress made on each objective is reported in the core of this summary and is
complemented by descriptions of how the laboratory, modelling and field measurements were combined in
an integrated way.
SCOUT-O3 has involved the research efforts of 70 partners with more than 100 scientific groups, and it has
taken full advantage of new and existing research facilities developed at a national level. In the next few
pages, prior to discussing the progress made, we give examples of how this large group of scientists have
collaborated to provide real advances in ths area.
5
Laboratory Measurements
Mimicking the Atmosphere The Reaction of HO2 with NO:
A New Route to HNO3 Formation
The behaviour and abundance of trace gases in the
atmosphere can only be fundamentally understood The reaction of HO2 with NO (both radicals) has
by examining the molecular properties of the gases traditionally been assumed to result in the formation
concerned. How stable are they? How fast do they of OH and NO2 (pathway A), the oxidation of NO
react with other gases? Are they easily adsorbed to NO2 being an important step in photochemical
onto particles? Do they react with or on particles? ozone production. By using a novel “turbulent-
Similarly, under what conditions do particles form flow” reactor coupled to a highly sensitive mass
and evaporate? The answers to these questions spectrometer, laboratory work in SCOUT-O3
can only be found by detailed laboratory studies of has however shown that a small fraction of this
individual processes. The focus of SCOUT-O3 on reaction results in generation of nitric acid (HNO3)
the cold tropopause region has thrown up a great as written below (pathway B):
challenge for laboratory work to produce high
quality datasets within a robust physical/chemical
framework at temperatures as low as -80ºC. HO2 + NO 4 OH + NO2 (A)
4 HNO3 (B)
Laboratory data enable us to produce accurate
and transferable parameterisations for use in The two reaction pathways: B is recently
models describing this part of the atmosphere. discovered and takes place just a few
The laboratory work has covered several aspects percent of the time.
of atmospheric chemistry and physics with major
foci on:
In pathway B, two radicals are converted to a long
• gas-phase reactions that generate and remove lived “reservoir” species, HNO3. Previous studies
reactive radicals and thus impact on lifetimes of this reaction were not sensitive enough to
and abundance of climate gases such as detect HNO3 as the fraction of reactive collisions
methane; between HO2 and NO that leads to HNO3 is small
• the removal of traces gases via interaction with
cirrus clouds; and
• the occurrence, properties and persistence of
cirrus clouds.
Trace gases from several chemical families have
been investigated including oxidised organics
(especially ketones, which are photochemical
sources of radicals) and inorganic acids (especially
nitric acid, a major reservoir of radicals). Some
highlights of the research results are outlined
below.
Cirrus are thin ice clouds that form at altitudes
of 7-17 km on existing aerosol particles.
6
(generally less than 1%) and depends on the overall
pressure, humidity and temperature. SCOUT-O3
modelling studies (see Atmospheric Models) show
that the formation of HNO3 even at low yield has
a profound impact on the radical budget of the
tropopause region.
The Interaction of Trace Gases with Cirrus Ice:
Partitioning between Gas and Ice Phases
Cirrus (ice cloud) coverage in the tropopause
region is high and the ice particles may provide
reactive surfaces for trace gas removal in this part
of the atmosphere. Results on heterogeneous
ice chemistry from SCOUT-O3 have revealed a
strong dependence of the strength of trace gas /
ice interactions on the properties of the trace gas.
Whereas ketones (e.g. acetone) and aldehydes are
weakly associated with ice surfaces, organic (e.g.
acetic) and inorganic acids such as HONO, H2O2
and HNO3 interact strongly.
The AIDA atmospheric simulation chamber at
For many species a simple empirical relationship Forschungzentrum Karslruhe can be cooled to low enough
between vapour pressure and ice affinity can be temperatures (-80ºC!) that “cirrus clouds” can form.
found. The laboratory work shows that nitric acid
(HNO3) has an exceptionally large affinity for ice, that form at altitudes of 7-17 km. The ice particles
the interaction being associated not only with the can contain mineral dust arising from deserts
surface but also involving underlying layers of the and organics originating from natural as well as
bulk ice sample. In order to reconcile laboratory anthropogenic emissions. One focus of laboratory
findings with field observations a model has been work within SCOUT-O3 was the investigation
developed that describes the “trapping” of HNO3 of how these different types of aerosol particles
in a growing ice particle under conditions pertinent affect the ice formation processes. For example,
to the tropopause region. The model captures the various forms of mineral dust particles facilitate
observed, almost complete HNO3 transfer from the the formation of ice, while some organics, in
gas to ice phase at sufficiently cold temperatures. particular the larger water soluble molecules,
inhibit ice formation, because they become
“gooey” at the very low temperatures below
The Formation of Cirrus Ice Clouds: Role of –70ºC. The laboratory studies were designed to
Heterogeneous Ice Nuclei and Organics produce parameterizations for use in atmospheric
cloud models. The experimental techniques that
The accurate representation of cirrus clouds in were used range from studies of individual cloud
atmospheric models requires knowledge of the droplets ~1/100 of a millimetre in size to millions
processes governing their formation, properties of droplets in chambers several stories high.
and lifetimes. Cirrus clouds consist of ice particles
7
Observing the Atmosphere
Background The observing stations in NDACC are global and
European scientists and institutions make a major
Atmospheric measurements have often led the contribution (e.g. through the EC GEOMON
way in developing new understanding of the project). The sites range from the tropics to the
fundamental phenomena - and sometimes even high latitudes in both hemispheres.
their existence. For example the existence of the
Brewer-Dobson circulation was first suggested by The scientific aims of NDACC, which align very
measurements of water vapour on high altitude well with those of SCOUT-O3, are:
aircraft in the 1940s, while the ozone hole was first
• detecting trends in atmospheric composition;
observed as a result of careful observations being
made in harsh conditions for nearly 30 years. • studying atmospheric composition variability
at interannual and longer timescales;
Nowadays, atmospheric observations fall into
three main, complementary categories: • establishing links and feedbacks between
climate change and atmospheric composition;
• long-term measurements;
• calibrating and validating space-based
• intensive field campaigns; measurements of the atmosphere;
• global views from satellites. • supporting process-focused scientific field
campaigns, and
All three types of measurement were involved in
SCOUT-O3. • testing and improving theoretical models of
the atmosphere.
Long term Measurements There is a paucity of sites in the Tropics and sub-
tropics, with only 7 sites between 30ºS and 30ºN
The long-term measurements in SCOUT-O3 were whose area is half the Earth’s surface. One of these,
centred around the Network for the Detection of at Izaña on Tenerife, opened in 1916 following
Atmosphere Composition Change (NDACC) many years of sporadic scientific visits to Tenerife
whose goal is to obtain high quality measurements including by Darwin and von Humboldt. The
of a broad range of atmospheric chemical species intensity of measurements picked up in the 1980s
and parameters. and Izaña joined the WMO’s Global Atmospheric
Watch when it formed in 1989.
8
Global Views from Satellites in the tropical UTLS meant there were real
opportunities to make new discoveries. In total, 6
The first systematic observations of the Earth’s field campaigns were organised in SCOUT-O3.
atmosphere by instruments carried on orbiting
satellites started in the late 1960s. Over the years 1. Darwin, Australia, Nov/Dec 2005. Scientists
the capabilities of the instruments have improved investigated the influence of the strong tropical
enormously, and measurements of the upper convection on the UTLS using several aircraft.
atmosphere and the Earth’s surface are now of 2. Thessaloniki, Greece, Aug 2006. The interaction
high quality. The upper troposphere and lower of clouds and aerosol with UV radiation was studied
stratosphere is one of the harder altitude ranges using aircraft and ground-based instruments.
to observe reliably as there is a lot of atmosphere
above it to look though and strong, complicating 3. Niamey, Niger, Aug/Sept 2006. In collaboration
features such as clouds below and even in it. with AMMA, the effect of the West African
Since 2000 the ESA Envisat, NASA AURA and Monsoon on the UTLS was observed with aircraft,
SSC ODIN (below) satellites were launched with balloons and ground stations.
instruments designed for observing the UTLS. 4. Mahé, Seychelles, Jan/ Feb 2008. Long duration
balloons capable of carrying instruments in the
In SCOUT-O3 measurements from instruments on stratosphere were launched.
the satellites, particularly ENVISAT and ODIN,
have been assessed for their quality and used to 5. Teresina, Brazil, June 2005 and June 2008. Large
study of the global and regional variations of many research balloons were launched with payloads
trace species in the UTLS. The measurements are which made detailed atmospheric observations
valuable in comparing with the global atmospheric and validated ESA satellite measurements.
models and providing the large-scale context for
long-term measurements and field campaigns.
Intensive Field Measurements 6. Niamey, Niger, Aug 2008. A second campaign
involving lightweight instruments and small
Field measurement campaigns are invaluable balloons was organised to look more at the effect
as they allow detailed investigation of critical of the West African Monsoon on the UTLS.
atmospheric processes. They were the central
experimental activity within SCOUT-O3, with The measurements from all these campaigns
airborne and balloon-borne measurements in are being interpreted using other available data
the UTLS focussed on chemical, microphysical, (e.g. satellite measurements and meteorological
transport and radiative processes in tropical analyses) as well as SCOUT-O3 models.
regions. The shortage of previous measurements
9
Atmospheric Models
What are Atmospheric Models? importance for recycling OH and NO2, can also
follow a reaction pathway which produces nitric
Our understanding of atmospheric processes is acid (see Laboratory Measurements). This
often encapsulated in numerical models, which pathway was previously unknown but modelling
are simply mathematical descriptions of the studies by SCOUT-O3 scientists showed that,
atmospheric system formulated on a computer. although the pathway is followed in only a
Because the atmosphere is so complex, different small fraction of the reactions, its importance
types of model have been developed for different for atmospheric chemistry is nevertheless very
uses. Some models contain detailed descriptions large. The figure shows the change in OH and
of the chemical processes, e.g. in an isolated ozone when the reaction is included. The impact
parcel of air, while others attempt to model the on the model fields is large, approaching 60% for
whole of the atmosphere, including all the climate OH and more than 20% for ozone. Modelling
and chemistry processes. They can simplify the has highlighted the imporantance of this reaction.
atmospheric system, for example, by specifying the Further investigation of this reaction in modelling
observed meteorological conditions and focussing and laboratory studies is merited.
just on chemical change. Other models attempt
to model just a local measurement or a local
process: some of the modelling which supported
the SCOUT-O3 field measurement campaigns in
Australia, Africa and South America falls into this
category. Finally models can be used to study
how the atmosphere might change in the future:
chemistry-climate models capable of modelling
how changes in climate affect atmospheric
composition particularly in the stratosphere. In
SCOUT-O3 these are used to investigate how
the ozone layer is affected by the reductions in
emissions of ozone-depleting substances and by
climate change.
We give examples of these different uses below.
Including the Latest Information
from the Laboratory
A major objective of SCOUT-O3 was to improve
our chemistry-climate models. One way of doing
this is to ensure that the best available laboratory
data on atmospheric chemical (e.g. reaction
pathways and rates) and physical processes (e.g.
properties of atmospheric particles) was included
in our models. Thus, work by laboratory chemists
within SCOUT-O3 showed that the reaction of
HO2 + NO, long known to be of atmospheric
10
Comparing Models with Improving Chemistry-Climate Models
Atmospheric Observations
Our improved chemistry-climate models have
A second way in which the models were improved been used to study how the ozone layer will
was by comparison with atmospheric data. The recover (and what will be the subsequent impact
concerted collection of data in our various on surface UV) following further phase-out of
field campaigns was an important part of this ozone depleting substances. The figure below
exercise. A major SCOUT-O3 research question gives one example, demonstrating that ‘recovery’
was whether our models represent accurately the depends not just on the future abundances of the
transport of species from the troposphere to the ozone depleting substances (ODS) but also on
stratosphere and, especially, whether transport greenhouse gas concentrations.
through the tropical tropopause, the major path
from troposphere to stratosphere, is treated well.
Air parcel trajectory models, mesoscale models
and global models were used to address these
questions.
One approach was to characterise in detail
the behaviour of the tropical tropopause in
our numerical models. How much transport
occurs through the region and in which specific
directions? Are there important spatial and
temporal differences? Other modelling studies The variation of tropical and Antartic ozone has
tried to reproduce the aircraft and balloon data been calculated in a SCOUT-O3 chemistry-climate
collected in tropical field campaigns. model. The model reproduces the observed decline
in ozone and then shows a gradual recovery during
the 21st century. The increase in greenhouse gas
concentrations causes the stratosphere to cool
which slows down the rate of ozone-destroying
reactions and, hence, leads to a faster recovery of
the ozone layer.
Chemistry-climate models can be used to study
a range of scenarios. In the ‘World Avoided’
section we show how models are used to address
what might have happened without the Montreal
Protocol.
The figure shows an idealized study of the transport
of a gas (this could represent one of the natural
halogen species which are believed to be emitted
by the tropical ocean) emitted in the tropics and
lifted towards the stratosphere.
11
Coordinated Activity 1:
Darwin Campaign
Chasing Hector – The campaign was based at the Royal Australian
The SCOUT-O3 Airborne Experiment Air Force base in Darwin in November and
December 2005. European scientists performed
The Tropics is the main region where air enters the extensive measurements of chemical species, of
stratosphere. An important step is upward transport aerosol properties and of cloud ice particles from
into the upper troposphere and occasionally the the high-flying M-55 Geophysica and the DLR
lower stratosphere in huge tropical thunderstorms. Falcon jet. Together with the two aircraft of the
These are particularly prominent over Indonesia, UK ACTIVE project and a Swiss Learjet, these
Micronesia and northern Australia, where strong activities formed the first phase of the “Tropical
convection occurs most frequently. Warm Pool International Cloud Experiment (TWP-
ICE)”, which was hosted by the Australian Bureau
The first campaign in SCOUT-O3 investigated a of Meteorology and ran from November 2005 to
storm system called Hector, which occurs almost February 2006. TWP-ICE involved scientists
daily during November and December over the from Australia, Europe, Russia and the USA. The
Tiwi Islands north of Darwin, Australia (11ºS, campaign attracted a good deal of press interest
131ºE). Intense Hectors reach to altitudes of up and featured in documentaries in Germany and
to 20 km, clearly in the lower stratosphere. The Australia as well as numerous press articles.
regularity and distinctness of Hector mean that
they have the potential to be studied in isolation.
Measurements at the bottom and the top give a
chance to see how quickly and how much travels
up from the ground.
The Geophysica left its mark after flying above the
top of a dissipating Hector. Care had to be taken to
avoid confusing the Geophysica’s contrail with air
On 30 November 2005 instruments on the
Geophysica measured ice particles in the
stratosphere up to at least the aircraft altitude.
In this case, “geysers” of ice stretch 600-700 m
into the stratosphere, seemingly connected to
the thunderstorm underneath. Other instruments
confirmed the presence of ice in the stratosphere
when the aircraft flew through the top of the
“geysers”.
12
Coordinated Activity 2:
Understanding Clouds, Aerosols and UV
Thessaloniki Measurement Campaign
Atmospheric particles (aerosols and clouds)
strongly influence the amount of solar radiation
reaching the Earth’s surface. However, a
quantitative description of how clouds and
aerosols change incoming UV radiation remain
elusive. SCOUT-O3 scientists organised a field
measurement campaign in northern Greece to
examine this in detail. Measurements of spectral
UV radiation, particle concentration, ozone and
other important atmospheric parameters were made
at a network of ground sites and on two aircraft
during two weeks in August 2006, using state of Ground instruments used to measure aerosol optical
the art instrumentation. The aircraft measurements properties and UV radiation at
the Aristotle University of Thessaloniki.
were used to determine the variations of aerosol
optical and physical properties over the wider area
and at different altitudes. New instruments and day-to-day aerosol variability which caused
methods for measuring accurately the intensity differences in UV radiation of up to 30%.
of UV radiation from the sky were used and were
compared to each other, revealing challenging Measurements from the campaign have been
issues to be considered in future. used in conjunction with numerical models
describing the propagation of radiation through
The airborne measurements revealed large the atmosphere to investigate quantitatively
variability of the aerosols over the wider area and the influences of aerosols on various radiative
at different altitudes, both with respect to their quantities. Good agreement within the uncertainty
physical and optical properties. However within limits has been achieved amongst single scattering
the city the spatial aerosol variations were small, albedo retrievals from airborne measurements and
caused by effective mixing of air in the atmospheric from the combination of photometric and LIDAR
layer below ~1 km, and showed a marked diurnal measurements.
pattern. The ground measurements showed large
Advanced 3D model calculations have
been used to simulate the polarization of
solar radiation by atmospheric particles.
By combining model calculations with
the measured optical properties of
aerosols, vertically resolved properties
of aerosols were retrieved. This
information can be used in radiation
Aerosols and clouds up to 3 km detected by the downward-looking Lidar modelling to improve the accuracy of
onboard the CESSNA aircraft. Two thin cloud layers in about 3.1 km UV radiation simulations.
and 2.5 km were observed during the whole observation period (orange),
aerosol structures were also visible at 1.5 km over certain areas (green).
13
Coordinated Activity 3:
SCOUT-O3 / AMMA Campaign
The West African Monsoon the effects of intense mesoscale convective systems
on the upper troposphere and lower stratosphere.
In July and August 2006 two EU FP6 Integrated Five scientific flights were successfully carried
Projects, SCOUT-O3 and AMMA, cooperated in out on site, and four transfer flights allowed a
a field measurement campaign investigating the characterization of the tropopause region along
effect of the West African Monsoon. The SCOUT- a latitudinal transect from southern Europe to
O3 emphasis was on the upper troposphere and West Africa. These flights were carried out in
lower stratosphere, while AMMA focussed more on conjunction with flights of the DLR Falcon. In
the lower atmosphere including assessing weather total 7 research balloon flights and 29 lightweight
forecasting ability, air quality and the impact on soundings were made at Niamey airport, as well
disease and agriculture. Overall the campaign as three low to mid level aircraft in AMMA. The
involved 5 aircraft, balloons and a network of research focussed on water vapour transport and
ground-based measurements. Of particular on high altitude clouds. Some balloon experiments
interest to SCOUT-O3, the M55 Geophysica and were damaged because of the very difficult
the DLR Falcon were based at Ouagadougou in conditions for recovery in a flood region.
Burkina-Faso, and the research balloons based The campaign activities, not originally planned
400 km away at Niamey in Niger. in SCOUT-O3, were mainly funded by national
institutions and exploited scientific and logistic
The M55 Geophysica flights aimed at a better infrastructures provided by the EC SCOUT-O3 and
understanding of the impact of the upward AMMA projects. This was an excellent example
transport and redistribution of water, aerosol, dust of scientific cooperation within Europe as well as
and chemical species, at assessing the effect of with the partners in several W. African countries.
lightning on the NOx production, and at studying
14
Coordinated Activity 4:
How good are the models?
Background CCMs represent physical, chemical, and dynamical
processes. An important element is to understand
When using an atmospheric model for scientific the ability of CCMs to reproduce past trends and
studies, it is important to know how well it variability.
performs, especially if the results are used to
inform policymakers – models should always be The CCMVal activity helps to coordinate CCM
used with their strengths and weaknesses in mind. model efforts around the world. In this way,
The interaction between the stratosphere and the CCM community can provide the maximum
climate change is complex, and so a major effort amount of useful scientific information for
in SCOUT-O3 was to test the models against the WMO/UNEP and IPCC assessments by
observations and against each other. This effort developing and maintaining evaluation tools for
involved several different types of model, but a the models, defining boundary conditions for
particular emphasis was put on the chemistry- “scenario” experiments, and archiving output
climate models (CCMs) used to simulate the data from the models. It is currently preparing
effects of different future scenarios as these studies a report assessing CCM performance which will
require extrapolation from current conditions. This provide an excellent basis for the UNEP/WMO
work has been based around the participation of Assessment in 2010. The role CCMVal and other
the SCOUT-O3 CCMs in the international SPARC SPARC initiatives play in supporting international
CCMVal initiative. Assessments underlies their importance and the
need to be international themselves.
SPARC CCMVal The success of such initiatives depends on whether
individual scientists benefit and get involved.
The goal of CCMVal is to improve understanding Many SCOUT-O3 scientists have participated
of CCMs by concentrating on specific processes in CCMVal since its inception with individuals
that are important in determining critical aspects playing leading roles in its organisation. Three
of the model performance such as Arctic and workshops were held during SCOUT-O3. 9
Antarctic ozone loss and the Brewer-Dobson modelling groups are participating through the
Circulation. It also provides a forum for discussion inclusion of results from their CCM and experts in
and coordinated analysis of science results. One the collection and analysis of observations provide
outcome has been improvements in how well the all-important measures to compare with.
15
Meeting the Objectives
Links between SCOUT-O3 Objectives and Activities
16
Meeting the Objectives
The Scientific Objectives
In order to address the central aim of SCOUT-O3, ten scientific objectives were identified which served as
the basis for the science plan. These were used to define the organisational structure which consisted of six
scientific and two supporting Activities (see SCOUT-O3 Approach). These are not discussed here as we
want to keep the emphasis on the results rather than the means used to achieve them.
1. Determination of air residence times in the tropical tropopause layer and assessment of the
transport of very short-lived ozone-depleting substances through the tropical tropopause layer;
2. The influence of clouds on the tropical upper troposphere and lower stratosphere;
3. Understanding the stratospheric water vapour trend and its consequences;
4. The stratospheric aerosol layer - role of the tropical tropopause layer and possible tropical
tropopause layer changes;
5. Past ultraviolet (UV) changes, variability and trends – Improved understanding of UV
modulation by aerosols and clouds;
6. Ozone variability and past changes at mid-latitudes;
7. Interannual variability in polar processes and likely changes in a changing atmosphere;
8. Improved understanding of the Brewer-Dobson and general stratospheric circulation;
9. Stratosphere / troposphere coupling - past and future; and
10. Predictions, based on a new generation of chemistry climate models, to consider (a) ozone
recovery, (b) the effect of climate change on the recovery, and (c) the impact of the ozone
change on surface UV
17
Objective 1:
Interest kilometers around the globe. Alternatively the very
strongest thunderstorms can carry air directly into
The large-scale circulation in the stratosphere the stratosphere, but the extent to which this can
is upwards in the tropics and downwards in the happen is not well known. Two aims in SCOUT-
extratropics. Air therefore enters the stratosphere O3 were to (a) quantify the relative importance
predominantly in the tropics, with the tropical of these two routes in determining stratospheric
upper troposphere, now often known as the composition and (b) provide good estimates of
Tropical Tropopause Layer (TTL), therefore acting how long air takes to pass through the Tropical
as a ‘gateway’ to the stratosphere. Relatively few Tropopause Layer.
detailed measurements have been made in the
TTL region, leaving many open questions. One of
these is how chemical compounds are transported Approach
from the Earth’s surface into the stratosphere.
Of particular interest are the very short-lived Unravelling the different factors that influence how
substances (VSLS) such as bromoform which different gases reach the stratosphere is a complex
could potentially be making an increasingly large problem. It involves atmospheric processes from
contribution to the stratospheric bromine amount. the local (individual thunderstorms) to the global
scale which operate on timescales from a few
hours to months and even years. The methods
used in SCOUT-O3 were:
• detailed measurements of trace gases lofted by
convective systems using aircraft and balloons
in S. America, N. Australia and W. Africa;
• development and use of models covering local
areas and scaling up to global models;
• analysis of satellite measurements to infer
global patterns; and
• calculations of uplift in the tropical UTLS
The quantity of VSLS which reaches the
using the latest meteorological data.
stratosphere is affected by a range of chemical and
meteorological factors. The bottom line is that
The work on tropical transport has been closely
they must reach the stratosphere within a few days
linked with the SCOUT-O3 chemistry-climate
or weeks of their release into the atmosphere as
models (e.g. through the SPARC CCMVal
they will otherwise be removed through oxidation
initiative) in order to improve their representation of
and rain-out. Uplift in strong convection is one
the composition of air entering the stratosphere.
possibility for this. While most tropical convection
carries large volumes or air up to 12 km or so,
most of this will subsequently descend. To reach
Findings
the stratosphere, air must be taken up in strong
convective storms to above about 14 km. From
Many individual studies of transport through the
here it can be taken up into the stratosphere by
TTL were made in SCOUT-O3 and only a few
slower vertical transport, perhaps taking several
examples can be highlighted here.
weeks during which time it can travel thousands of
18
Through the Tropical Tropopause Layer (TTL)
Importance of Convection measurements. As such they provide as direct a
The strongest evidence for the injection of air into comparison as possible with field measurements.
the stratosphere during convective events comes
from in situ measurements of water vapour and
particles. The signatures of local injection of
trace gases such as CO or O3 is harder to identify
in large part because of the influence of air from
further away. It is thus hard to quantify how much
air is injected through strong convective events.
On a larger scale, analysis of satellite measurements The comparisons (here shown for CO observed
provides stronger evidence for the seasonal during a flight in the SCOUT-O3 Darwin campaign
importance of strong convection over central Africa for two CCMs and two other global models) are
during March to May, earlier than and to the south surprisingly good. The models cannot be expected
of the campaigns in July to September. These to reproduce all the fine scale structure as their
results are intriguing as they are not explicable resolution is much coarser, and these results are very
using the best available meteorological data. encouraging. Complementary work comparing
SCOUT-O3 and other models with other data is
Measurements around thunderstorms have better being carried out in SPARC CCMVal and overall
quantified the production rate of nitrogen oxides in the effect will be a significant improvement in how
tropical storms. Such information was relatively convection is represented in the models.
sparse previously and it is important because
thunderstorms are one of the natural sources to Residence Time of Air in the TTL
compare with the emissions from aircraft. The latest meteorological reanalyses (see
Objective 3) have been used to provide better
Comparison with CCMs and Other Models estimates of how long it takes for air to rise into
A major aim in the latter part of SCOUT-O3 has the stratosphere from where it emerges from
been to improve the models using the available convective clouds. These estimates are valuable
measurements. A particular focus has been how in assessing how much chemical removal of VSLS
models represent transport in convection as they can take place in air being transported up in this
struggle to provide realistic estimates of the future way. When coupled with in situ measurements of
input of air into the stratosphere. The trace gas bromine compounds from aircraft and balloons,
measurements from the field campaigns have been they provide some useful constraints on the
compared to a range of models, including some possible global importance of VSLS. Tightening
‘nudged’ CCMs. These models are versions of these constraints requires further work combining
the CCMs used to look at future scenarios except both improved estimates of timescales and more
that they are constrained (i.e. nudged) using precise observations.
meteorological information for the period of the
19
Objective 2:
Interest TTL on stratospheric ozone. So, SCOUT-O3 set
itself five goals:
Clouds are present throughout the Tropics and
strongly influence the Earth’s energy balance. • To make measurements of ice clouds and
They reflect incoming sunlight and absorb aerosol particles in the tropical UTLS;
energy emitted by the underlying land, ocean and • To carry out laboratory studies of critical
atmosphere. The processes controlling tropical processes in ice and aerosol particles;
cloudiness in a changing climate thus need to be
understood. Tropical clouds are also critical in • To undertake computer modelling of ice
determining how water enters the stratosphere (see clouds in the tropical UTLS;
Objective 3) and so influence the ozone layer. • To assess the role of climate (change) on
cloudiness in the tropical UTLS; and
• To produce simple computer modules
representing the interaction of gases with ice
particles to improve global climate models.
Findings
Ice Clouds and Glass Particles
The tiny aerosol particles that are present in
the atmosphere promote ice particle formation.
However, the ability of an aerosol particle to
The highest clouds in the Tropics are cirrus which promote ice formation depends very much
are present at altitudes from 12 to 17 km. About half on what the particle is made of. Organic
of them are directly associated with thunderstorms. compounds make up 60-80% of the mass of
Humid air is rapidly lofted to high altitudes until aerosol particles in the upper troposphere where
the local temperature is low enough that the water cirrus clouds form; sulfuric acid makes up most
condenses. Anvils from the top of thunderstorms of the rest. The organic fraction of the aerosol
and cirrus clouds often remain as the anvils disperse. is composed of many different compounds, and
Most of the thunderstorm remnants occur at about these mixtures do not crystallise easily. Instead,
14 km altitude, some 2-3 km below the stratosphere, they tend to form liquid solutions and non-
although some very strong storms reach much crystalline solids (i.e. glasses). Liquids become
higher (20 km). The rest of the cirrus is produced very “gooey” (viscous) as temperature decreases:
by atmospheric motions that lift air more gently. at 200 K (-73°C) - a temperature typical of the
upper troposphere - sulfuric acid is about as
viscous as honey. Organic aerosol particles
Approach are even more viscous at these temperatures.
When liquids become so gooey that they act
To assess how sensitive TTL cloudiness is to like solids, they have become a glass. During
climate, it is necessary to understand better the SCOUT-O3, laboratory work has shown that the
TTL as it is now. Only then can we quantify the formation of glassy aerosol particles may have
feedbacks that control the sensitivity of the TTL profound effects on ice formation in the upper
to climate, and assess the impact of clouds in the troposphere.
20
Clouds in the tropical upper troposphere and
lower stratosphere
Most ice formation in the upper troposphere
comes about by liquid aerosol particles taking up
water as the air cools, until the point is reached
at which ice can form spontaneously in the liquid
particle. If, however, the temperature at which
an aerosol particle turns glassy is higher than the
temperature at which ice formation can occur, then
ice formation will be inhibited. decades. As the model is extended in space (i.e.
from a point in space to 1, 2 and 3D) and time
The Supersaturation Puzzle (from hours to decades), the amount of detail about
Another longstanding puzzle connected to the ice clouds that can be incorporated diminishes.
atmospheric water vapour was the series of in situ By using a hierarchy of computer models we can
measurements which showed surprisingly large interpret the observations in detail, and work out
volumes of air where no ice clouds had formed what is going wrong if the simple ice physics
despite sufficiently low temperatures and high in the global models misses some part of the
water vapour amounts (supersaturation). While observed behaviour of the clouds. For example,
this puzzle is still not completely solved, a great SCOUT-O3 scientists showed that ice is
deal of progress has been made. First, a rigorous injected into the stratosphere above super-strong
reanalysis of one of the largest available sets of thunderstorms.
measurements found a reduced incidence of cases
where supersaturation was observed. Second, the When similar cirrus simulations are carried out
fact that the saturation pressure above glasses is within climate models, the effect on the Earth’s
greater than above ice (above) might explain some energy balance can be calculated. This turns out to
of the observed supersaturation (see Objective 2). be difficult for two reasons: (i) the net effect of ice
clouds is the relatively small difference between
Simulating Cloudiness the amount of sunlight reflected back to space
SCOUT-O3 has analysed satellite data to provide and the amount of re-emitted energy absorbed,
global maps of cirrus and aerosol particles. There and (ii) we don’t have sufficient understanding of
are many new observations with which to compare the relative importance of different ice formation
computer models and from which, along with the routes in the upper troposphere. SCOUT-O3 has
laboratory results, to improve those models. The gone a long way to addressing our uncertainties
computer models of clouds used in SCOUT-O3 about ice-cloudiness, and its impacts, but important
range from relatively simple calculations that research questions remain.
follow an individual parcel of air, through 3D
simulations that can capture cloud shapes and
properties for a few hours, all the way to global
climate-and-chemistry simulations covering many
21
Objective 3:
Interest Approach
The stratosphere contains very little water (~5 There are many aspects to understanding water
parts per million) compared to the troposphere vapour’s role in the stratosphere, and so a multi-
(up to a few percent), and the gradient across the pronged approach has been adopted:
tropopause is large. There have been vigorous
discussions about the causes for several decades, • Studies of the latest re-analysis of historical
ever since the first stratospheric water vapour data giving the best picture of the meteorology
measurements were made in the late 1940s. Air for the last half century;
enters the stratosphere in the Tropics where the • Detailed observations during field
tropopause is coldest (reaching –90°C), and the low measurement campaigns in North Australia
temperatures ‘freeze dry’ the air. However there has and West Africa;
not been agreement as to whether this dehydration
occurs when air is lifted slowly over large areas or • Process studies using measurements and
rapidly in large, violent thunderstorms. models; and
• New and improved global measurements from
Atmospheric measurements indicate that satellite instruments.
stratospheric water vapour concentrations have
increased. From 1980, when more measurements The work performed in the approaches has been
became available, to 2000, stratospheric water closely integrated with the laboratory work on ice
vapour increased at a rate of 0.6% per year particles and the global studies of water vapour
continuing a previous, though less well observed using chemistry-climate models.
trend. In 2000, a sudden drop was identified.
These are important changes on a global basis and
need to be understood because of the importance Findings
of water vapour for (a) the radiative balance and
chemistry of the stratosphere and (b) the feedback How Water Enters the Stratosphere
on climate in the troposphere. The main factor that determines how much
water remains in an air parcel which enters the
stratosphere is the lowest temperature that parcel
Field work in the Tropics is very
demanding and frequently means that
instruments have to be prepared in hot,
humid conditions (hotter than 30°C, 100%
relative humidity) in order to make high
altitude measurements at -90°C in very
dry air. Here a balloon instrument is
being prepared in Niamey Airport during
22
Understanding Stratospheric Water Vapour
experiences. In principle an air parcel could Recent Changes
pass through the cold tropopause region either At the start of SCOUT-O3, a great deal of attention
by travelling large distances horizontally while was being paid to the long-term increase in
rising slowly upward, or in fast upward motion of stratospheric water vapour. Analyses of satellite
air in, for example, a tropical storm. The latest
meteorological re-analyses are the best current
estimates of the winds, temperatures and other
atmospheric properties for several decades and
can be used to calculate year-to-year variation
of how air moves into the stratosphere, what
temperatures are experienced and the implications
for stratospheric water vapour. These calculations
would be very inaccurate if rapid upward motion
in individual tropical storms was the most
common route into the stratosphere. The excellent
reproduction of the interannual variability in
stratospheric water vapour suggests that most air
measurements of the past few years shows that
water vapour was low from 2002-2004, increased
a little from 2004 onwards, perhaps even reached
its 2001 value in early 2008. Temperatures at the
tropical tropopause are broadly consistent with
these changes. Overall, stratospheric water vapour
enters the stratosphere quasi-horizontally with just was lower in 2002-2007 than in 1995-2000. This
slow upward movement. In this way it experiences,
and its stratospheric water vapour amount is set
by, the extremely low tropopause temperatures
over the West Pacific.
The Role of Convection
Measurements made in North Australia and in
West Africa show that the super-strong storms
which penetrate into the stratosphere actually
inject water in the form of ice cyrstals that cause
local moistening rather than local drying as was behaviour appears to be a multi-year dynamical
thought for a long time. It is hard to provide a variation and there is not compelling evidence of
firm estimate of the global importance of such any secular trend. It underlines the importance
storms as their size and intensity varies so much of high quality, long-term measurements and
regionally and seasonally. Preliminary estimates the value of instrument comparisons such as the
from SCOUT-O3 indicate that the contribution to SPARC AQUAVIT initiative in which SCOUT-O3
the global stratospheric water vapour budget could groups are participated.
range from a few percent to a few tens of percent.
23
Objective 4:
Interest These have been studied using new in situ
observations from the tropical field measurement
Atmospheric aerosol particles are extremely small campaigns over Australia, Africa and Brazil, as
solid and liquid particles that play an important well as remote observations from the lidar onboard
role in the upper troposphere and the stratosphere. the CALIPSO US-French satellite.
They influence the energy budget of the atmosphere
by scattering incoming solar radiation; they act as In addition, since the episodic and unpredictable
condensation nuclei on which cirrus cloud and polar nature of volcanoes means that their future impact
stratospheric cloud droplets can form; and they depends on the halogen loading at the time of the
provide surfaces for the heterogeneous reactions eruption, the possible effects of weak and strong
that play a central role in ozone chemistry. volcanic eruptions have been assessed in CCMs
with improved descriptions of the stratospheric
Most of these aerosol particles result from the aerosol.
conversion of gaseous precursor sulphur gases
(SO2, CS2 and OCS) into sulphuric acid droplets.
These are particularly enhanced after a major
volcanic eruption, like that of the Pinatubo in the Findings
Philippines in 1991 which led to low ozone values
for several years. There have not been any major Particle composition in the TTL
volcanoes since Pinatubo and so the stratospheric The composition of particles in the TTL is important
aerosol has been relatively unperturbed during in determining their chemical reactivity and their
SCOUT-O3. This has confirmed that there is no ability to grow and/or nucleate cloud particles that
long-term trend in stratospheric aerosol resulting can, for example, lead to dehydration of air entering
from human activities such as aviation. Other the stratosphere. Particles containing reactive
classes of aerosol particles include mineral dust nitrogen have been detected near and below the
(lofted in storms), sooty smoke from biomass fires tropopause over Africa by instruments on the M55
and meteoritic particles. These classes are known Geophysica. Such nitric acid trihydrate particles
as non-volatile aerosol particles because — unlike are similar to the polar stratospheric clouds
the sulphuric acid droplets — they do not evaporate forming at low temperature in the Arctic and
when they are heated to 200°C. Antarctic. Satellite observations suggest that they
might nucleate on ice fed by convective activity.
Approach Ultra-fine, non-volatile particles have been
measured in the TTL during the same aircraft
The main areas of research in SCOUT-O3 are: flights, with large variations seen near the
• the fraction of aerosol particles that are non- tropopause. Though of still unknown nature in the
volatile, absence of chemical analysis, they are suspected
to result from deep convection from the boundary
• the role of the frequent small volcanoes layer.
erupting at low altitude;
Geyser-like injections of ice particles above
• the convective lifting of mineral dust or smoke
the tropopause have been observed on several
and more generally, and
occasions from aircraft and balloons over land
• the transport of precursor gases and particles convective systems. Simultaneous electric field
into the lower stratosphere. measurements on board the same balloon indicate
24
Stratospheric Aerosol Layer
(a) that this plume (as well as a lower altitude one
from a second volcano, Tavurvur, which erupted
in October 2006) was then slowly transported
upward up to 25 km by the Brewer-Dobson
circulation and (b) that small volcanoes contribute
to the aerosol load of the mid-stratosphere. These
measurements also demonstrate the existence of
a stagnant layer of minimum vertical velocity
around 20 km, and a surprisingly fast cleansing of
the lower stratosphere by the injection of particle-
free air from the troposphere up to 20 km during
the Southern Hemisphere convective season.
The future impact of volcanoes
The size distribution of stratospheric aerosols has
a strong influence on climate and on stratospheric
chemistry, and it is important to assess the abilities
that these particles were electrically charged. This of different descriptions of aerosols in CCMs.
would affect the buoyancy of the particles as well Under background (low aerosol) conditions the
as their ability either to grow or to evaporate. If this agreement was good, but there was large scatter in
effect is widespread, this finding would open up a simulations of volcanic eruptions.
new area of research on the role of thunderstorms
on the stratosphere. The radiative impact of future large volcanoes on
Volcanic eruptions
In August 2006, a layer of sulphuric acid water
droplets was observed over Africa around 20 km
by all aircraft and balloon particle instruments.
These were in the plume following the eruption of
the stratospheric circulation was studied to see
if the sensitivity of the stratosphere is likely to
change as climate changes. In the scenario used
(large volcanic eruptions in the Tropics in 2025
and 2035), a faster circulation is found as a result
of greater tropical upwelling with an indication
of a larger response in 2035. This process
the Soufrière Hills in the Caribbean in early May. manifests itself in transient heating in the lower
The evolution of the stratospheric aerosol during the stratosphere.
two years following the launch of CALIPSO show
25
Objective 5:
Interest Approach
Reliable prediction of the future evolution of The scientific objectives are addressed by:
surface UV radiation is required to serve European
policy makers in planning appropriate protection • exploiting and re-evaluating high quality
measures for public health. The UV radiation measurements of UV radiation from across
levels at the Earth’s surface are controlled mainly Europe to determine its variability and its
by atmospheric ozone, clouds, aerosols and relations with other atmospheric factors;
albedo. The depletion of stratospheric ozone • reconstructing old measurement records by
since the late 1970s has resulted in elevated levels using state-of-the-art radiative transfer models;
of UV radiation in many regions worldwide. As
a result of the successful implementation of the • making detailed measurements of UV
Montreal Protocol atmospheric concentrations of radiation and aerosols from the ground and
CFCs have started to decrease and the first signs from the air to improve our knowledge of how
of ozone recovery have been reported, prompting aerosols affect how solar UV radiation passes
the expectation of a corresponding reduction in through the atmosphere;
surface UV radiation levels. However, clouds, • using climate chemistry models in order to
aerosols and albedo are strongly influenced by simulate UV radiation in the 21st century,
climate change and they are expected to either taking in to consideration also the influence of
mask or enhance the impact of ozone recovery climate change on clouds, aerosols and albedo.
on UV radiation. The way these factors affect
UV radiation is complex involving synergistic
processes of absorption and scattering. Taking
into consideration the complexity of all these
processes, prediction of future UV radiation levels
on global scale remains a challenging task.
26
Past Surface UV Changes, Variability and Trends
Findings
Surface UV measurements made in Thessaloniki, Jokioinen, Sodankylä, Bilthoven, Hradec Kralove,
Norrköping, Potsdam and Lindenberg during the 1990s and 2000s have been re-evaluated and quality
controlled datasets produced. These measurements have been analysed to quantify the changes in surface
UV radiation, resulting from ozone depletion and from changes in clouds and aerosols over Europe. The
cleaning of the atmosphere due to decreasing aerosols results in increasing of UV irradiance counteracting
the effect from the slowdown of ozone depletion.
Reconstruction models have been developed to extend the UV records back to the 1960s providing a longer
period of data for the estimation of long term changes. UV levels have gradually increased over the last
3-4 decades. Ozone depletion has contributed to this change particularly at the high latitude sites, but the
diminishing thickness of aerosols over the same period played an important role. Cloudiness decreased solar
radiation at many sites up to the early 1990s. Since then, decreasing cloudiness has contributed to an increase
in surface UV radiation.
In response to the projected ozone recovery, surface erythemal irradiance under cloud-free skies is projected
to decrease between 2000 and 2100 by up to 5% over northern and 10% over southern mid-latitudes. At
southern high latitudes the average decrease is three times as much. This information is then used to improved
the atmospheric models describing how UV is transmitted through the atmosphere.
Projections of future UV radiation levels have been derived by combining radiative transfer model calculations
with outputs from CCMs. In response to the projected ozone recovery, surface erythemal irradiance under
cloud-free skies is projected to decrease between 2000 and 2100 by up to 5% over northern and 10% over
southern midlatitudes. At southern high latitudes the average decrease is three times as much as a result
of the calculated recovery of the ozone hole. Accounting also for changes in cloudiness derived from one
CCM, the decreases in surface erythemal
irradiance become smaller at mid-latitudes
and increase at high latitudes. Localized
increases are projected in the tropical zone
as a consequence of regional changes in
clouds.
The day-to-day changes of daily erythemal
irradiation doses derived from two CCMs
agree well with those derived from
measurements, except at high latitudes
in the winter months. The agreement is
worse when comparing absolute values,
owing to differences between the actual
and simulated ozone columns and clouds,
but these are encouraging results given that
this is the first time such a study has been
made.
27
Objective 6:
Interest Unravelling the relationship between ODS
emissions (top), concentrations (middle) and total
The possibility of depletion of the ozone layer was ozone (bottom) is needed to see how the Montreal
first raised in the early 1970s, but there was no Protocol has affected the mid-latitude ozone
evidence of a trend in the observations. However, layer. However, to do so requires quantitative
by the mid to late 1980s decreasing ozone amounts understanding of the factors that control the
were observed at polar and middle latitudes which variability of ozone which demands great care,
resulted from the release of Ozone Depleting even for the longest measurement record from
Substances (ODS) such as chlorofluorocarbons Arosa, Switzerland.
and Halons. Meanwhile, in response to the threat
of ozone destruction, the Vienna Convention was It requires, in particular, quantification of the
signed in 1985. The Montreal Protocol which limits relative importance of chemical and dynamical
the emissions of ODS was signed in 1987. The influences on stratospheric ozone changes.
implementation of the Montreal Protocol process, Uncertainty in these limits our ability to interpret
which allowed for strengthening amendments, has the past changes of the ozone layer as well as our
successfully resulted in reduced global production confidence in predictions of its future evolution.
of ODS (and, with a small delay, emissions) from
the end of the 1980s. In turn, this has led to a
more recent decline of the effective stratospheric Approach
chlorine loading (EESC) by about 6% since its
peak in the late 1990s. The goals in SCOUT-O3 were to
• quantify the effect of variability in transport
processes on extra-tropical total O3 variability;
• quantify the natural and anthropogenic
influences on the observed past changes;
• perform multi-decadal simulations of key
species in past atmosphere; and
• incorporate new laboratory data into model
calculations.
These were achieved by analysis of observations,
model improvements and model studies
Findings
Interannual variability
The Brewer-Dobson circulation is critical in
determining the amount of ozone over middle
and high latitudes in winter and spring as it
cause the ozone to increase following its annual
28
Ozone at Mid-Latitudes
minimum in autumn. The observed winter ozone better description of the long-term features in the
gain connected with transport of ozone from stratospheric circulation. As a result of all these
low to high latitudes has been found to correlate factors, SCOUT-O3 modellers have made the first
strongly with the upward transfer of energy from successful multi-decadal simulations of the whole
the troposphere and can be used to diagnose the stratosphere with reanalysed datasets to quantify
relationship between the state of stratospheric the role of halogens in global ozone trends.
dynamics and stratospheric ozone depletion.
Analysis of longer time periods indicates a change
of this correlation with time but it is unclear if this 3D Model Calculations of Ozone Changes
change also indicates changes of the circulation. 35N-60N
The models are much more successful in
reproducing the observed trends in the Northern
hemisphere than in the Southern hemisphere.
Resolving this issue will be needed before we can
claim a full understanding of the past stratospheric
ozone changes.
Other studies have investigated the importance of
processes in the lower stratosphere in determining
the ozone amount and variability. In particular
transport from the tropical upper troposphere into
the extratropical lower stratosphere is an important
factor in the annual cycle of ozone.
Improved understanding of trends
Our ability to reproduce past ozone trends has
improved significantly during SCOUT-O3. The
relative roles of transport and chemical depletion
are now much clearer, and the short-lived bromine
compounds have been found to be important
during the period following the eruption of the Mt
Pinatubo in 1991.
A major advance has been the use of the improved
meteorological reanalyses which have led to a
29
Objective 7:
Interest between ozone loss and climate change are
poorly understood and the importance of climate
The annual occurrence of the Antarctic ozone variability and change for the long-term evolution
hole is probably the best known example of where of chemical Arctic ozone loss is not known. The
human activity has had an impact on the Earth’s objectives of SCOUT-O3 project in polar science
atmosphere. It is a dramatic feature with all the were thus to:
ozone at altitudes between 15 and 20 km destroyed
each spring over all Antarctica. Smaller, but • advance our understanding of these processes;
significant losses (of up to 60% locally occur in • continue monitoring polar ozone loss in both
the Arctic winter, albeit with a large interannual hemispheres;
variability.
• assess the impact of climate change on polar
ozone loss; and
• provide realistic representations of polar
processes in chemistry-climate models.
Approach
The SCOUT-O3 approach was threefold. A
major element was to supplement and coordinate
nationally funded stratospheric observational
programmes in polar regions. A second element
was to analyse all available observations (new and
Polar stratospheric clouds (PSCs), such as these existing; ground-based and satellite) in order to
observed over Sodankyla in Northern Finland, understand the interannual variability better. The
must form for rapid chemical ozone loss to occur. third element was to improve the descriptions of
Stratospheric conditions are such that the Antarctic polar ozone loss in chemistry-climate models and
winter stratosphere is very cold and PSCs form to make better predictions of ozone will evolve in
every winter, while the Arctic is warmer and more the coming decades.
variable so that PSCs form less regularly. As a
result, large ozone losses occur every spring in the
Antarctic and in the Arctic ozone losses are large
in some winters and small in others.
The polar ozone losses have potentially large
effects on the climate system through their impact
on the radiative balance and the dynamical motions
of the atmosphere. For example, the ozone hole
has offset some of the surface warming caused
by CO2 and other greenhouse gases, an offset that
will disappear as the ozone hole recovers in the
coming decades. However, while these effects
are potentially large, the mutual interactions
30
Polar Ozone in a Changing Atmosphere
Findings Polar ozone loss and climate change
The impact of climate change on Arctic ozone loss
Quantifying ozone loss has been assessed using the extended series of
Stratospheric ozone losses in both hemispheres observed ozone losses in Arctic winters. Early in
have been quantified for each winter during SCOUT-O3, the climate sensitivity of Arctic ozone
SCOUT-O3 and the related uncertainties have loss determined from observations was found
been better characterized. For the Arctic, ozone to be significantly larger than predicted by the
loss has been estimated in near real-time and the state-of-the-art model at that time. Subsequently,
public was informed when unusually large losses improvements in the models largely eliminated
occurred. The most notable instance was in spring this problem and resulted in a much improved
2005 when losses of over 50% occurred at altitudes representation of the climate sensitivity in the
around 18 km, and there was a 30% depletion in model, giving greater faith in the model predictions
the atmospheric column of ozone. of Arctic ozone loss.
Finally, SCOUT-O3 scientists found that while
little change in temperature has occurred in the
warm Arctic winters, the coldest Arctic winters
have become significantly colder over the past four
decades. The role of these changes in stratospheric
Understanding critical processes
A combination of stratospheric observations and
detailed modeling has advanced our theoretical
understanding of the polar ozone loss process
by helping to identify the critical, rate-limiting
processes. In parallel, the year-to-year variation
in the natural dynamical variability (including climate is to enhance the large Arctic ozone losses
the effect of the Brewer-Dobson Circulation (see observed in the cold winters since the mid-1990s.
Objective 8) is better quantified. Together, these The cause of this change is not understood or
have led to better quantitative modelling of polar reproduced in climate models, but it could lead to
ozone loss in the 3D global models, which can an amplification of ozone loss in the next decade
now better reproduce the interannual variation of or so while halogen levels remain high.
chemical ozone losses in the Arctic. In addition,
the chemical and dynamical effects on stratospheric
ozone is responsible for a significant fraction of
the tropospheric climate and ozone variability.
31
Objective 8:
Interest and the mean transport time of stratospheric air and
the correlation of the winter ozone gain and eddy
Whereas wind speeds in the stratosphere easily heat flux. Observations are used to evaluate the
can reach several hundred of kilometre per hour results derived from CCM simulations. Scenario
and can sweep air latitudinally around the world calculations performed with CCMs are used to
in a few days, air only moves slowly from the improve our understanding of processes causing
Tropics to the Poles. As a result, it can take changes of the Brewer-Dobson circulation and its
years for tropospheric air parcels from entering possible future evolution.
the stratosphere in the tropics to leave it at polar
latitudes again. Yet it is this circulation (the
Brewer-Dobson circulation) which determines the Findings
distribution and thickness of the ozone layer, the
distribution of water vapour in the stratosphere, Observations of the ‘Age’ of Air
and the atmospheric lifetimes of many greenhouse The mean time taken to transport air from the
gases and ozone depleting substances (ODSs). It tropical lower stratosphere, where tropospheric
is characterised by upward motion of air in the air enters the stratosphere, to any point in the
tropics from the troposphere into the stratosphere stratosphere, is called the “age” of air. It can be
poleward transport in the stratosphere and eventual found from observations of inert trace gases which
mixing back into the high latitude troposphere. It have a clear trend. The spatial distribution of these
is more pronounced in the winter hemisphere. transport times results from the Brewer-Dobson
circulation.
Climate change is expected to alter the strength
of the Brewer-Dobson circulation. A stronger
circulation would tend to warm the extra-tropical
regions and cool the tropics and, in addition
would have direct implications for the transport of
tropospheric source gases into the stratosphere and
of stratospheric ozone into the troposphere. It is
therefore important to improve the observational
and theoretical understanding of the Brewer-
Dobson circulation.
Approach
Within SCOUT-O3, the approach is to use multi-
year observations of long-lived trace gases (e.g. In SCOUT-O3, the first global distribution of the age
derived from satellite instrument measurements) of air using observations of sulphur hexafluoride
in combination with decadal simulations by (SF6) has been obtained from ESA’s MIPAS/
numerical models of the atmosphere in order to ENVISAT instrument. The new measurements
investigate the variability and long-term temporal reach all the way to 40 km and allow the age of
evolution of stratospheric circulation. Important air to be derived throughout the stratosphere.
quantities are the tropical ascent rate of air masses Now spanning seven years of observations these
which can be determined from different methods data will provide a basis for future assessment of
like the H2O tape recorder, diabatic heating rates, circulation changes.
32
The Brewer-Dobson Circulation
Modelling the Current Atmosphere the upper troposphere and lower stratosphere,
Several chemical-transport models have been leading to an enhanced transfer of energy into the
improved following detailed comparisons with stratosphere.
other models, observations and new estimates
of ascent rates in the tropical lower stratosphere. The strengthening might be related to higher
In addition strategies were developed to use the tropical sea surface temperatures which could
meteorological analyses. The resulting multi- amplify deep convection locally and produce
annual simulations show a slight acceleration of an intensified upwelling in the tropical upper
the Brewer-Dobson circulation over the past 30 troposphere and lower stratosphere. The transport
years which seems to be in contrast with a new change in turn would increase the flux of ozone-
analysis of several decades of observations from poor tropospheric air into the tropical lower
balloons and aircraft which show a small increase stratosphere.
in the age of air.
Some CCM calculations indicate that the
The strength of the Brewer-Dobson circulation intensification of tropical upwelling in the lower
varies considerably from year to year and this has stratosphere will nearly double between the
been found to have a direct effect on the ozone periods1960-2000 and 2000-2040 due to the
over middle and higher latitudes (see Objective 6). combination of the radiative effect of greenhouse
It is important to see how this might change over gases (GHG) and the impact of higher sea surface
time. temperatures (SST).
Modelling the Future Atmosphere Whether the exact mechanism is correct or not, it
While observations have not provided a complete is clear that future changes in the Brewer-Dobson
picture of trends of the Brewer-Dobson circulation circulation (and of ozone and UV radiation) are
to date, several climate model studies indicate that sensitive to the sea surface temperatures used in
the circulation will strengthen as greenhouse gas the models. This highlights the importance of
concentrations rise. Although this strengthening developing and using CCMs which are coupled
is a robust feature of many climate change with good ocean models in order to determine
simulations, the underlying mechanisms are not the full response of the stratosphere to climate
sufficiently understood to explain the cause and change.
effect relationship. The amplification may result
from the calculated increase in the temperature
gradient between lower and higher latitudes in
33
Objective 9:
Interest Findings
The division of the lower part of the atmosphere into The Dynamical Effect of the Troposphere on the
troposphere and stratosphere is a convenience that Stratosphere
has been used by meteorologists and atmospheric The pattern of weather systems in the troposphere
chemists alike. In practice the troposphere and produces large-scale waves which disturb the
stratosphere are strongly coupled, both through polar vortex and lead to geographical variations of
dynamics and through chemical transport. The temperature and chemicals. SCOUT-O3 and other
coupling is two-way, i.e. the troposphere affects the work shows a clear link between waves leaving
stratosphere and vice versa. Tropospheric weather the troposphere and, for example, column ozone
and climate both affect the stratosphere and in in the stratosphere (see Objective 6).
turn are influenced by it. The troposphere acts as
a source for chemical species that are important More challenging is to identify particular patterns
in the stratosphere, both for ozone distribution of disturbance in the tropospheric circulation
and because their distribution in the stratosphere which have a large effect on the stratosphere. One
affects the radiation balance of the atmosphere important aspect of year-to-year variability in the
as a whole. Conversely the stratosphere is an stratosphere is the frequency of polar stratospheric
important source of ozone for the troposphere cloud (PSC) formation (and hence the potential for
and model simulations suggest, e.g., that future chemical ozone loss). SCOUT-O3 has shown this
changes in stratospheric ozone may significantly is strongly affected by the large-scale meteorology
increase background concentrations of ozone in the in the troposphere and that large PSC volumes are
troposphere. Concentrations of chemical species preceded by a tropospheric circulation with higher
such as ozone and water vapour vary sharply across than usual pressure over East Asia, associated
the tropopause, and it is important to understand with high pressure systems, and lower than usual
how such steep gradients are maintained. pressure over the Atlantic.
Approach
H
Understanding the coupling and ensuring that it
is properly represented in models is an important
part of understanding observed changes in the
atmosphere and in making reliable predictions
about the future. The issue of coupling between the
stratosphere and troposphere is large and diverse.
In SCOUT-O3, the effort has been focussed on
certain important and carefully selected questions
most closely connected to the overall project goal.
Broadly these can be classed into three groups:
The Dynamical Effect of the Stratosphere on the
• the dynamical effect of the troposphere on the Troposphere
stratosphere; Recent observational and modelling studies
• the dynamical effect of the stratosphere on the have shown that changes to the stratosphere, e.g.
troposphere; and destruction of stratospheric ozone in the Southern
hemisphere spring to form the Ozone Hole, have a
• chemical coupling. significant effect on tropospheric circulation. Thus
34
Stratosphere-Troposphere Coupling:
Past and Future
stratospheric changes on timescales ranging from (A)
weeks to decades must be properly represented in
models in order to provide reliable predictions of
weather and climate. Work in SCOUT-O3 relevant
to medium-range weather forecasting has found
that dynamical patterns in the lower stratosphere
can improve predictions of European temperatures.
The work has identified optimal patterns on which
to base such predictions. However it is a complex
issue and the whole subject of what aspects of
stratospheric dynamics and chemistry most need
to be included in models to improve predictions
of surface weather and climate is a fertile area of
investigation for the future. (B)
Chemical Coupling
Investigations of the factors influencing chemical
composition around the extratropical tropopause
have been model-based, using particle-based
methods to quantify transport. These provide
estimates of chemical distributions that can be
compared against in situ chemical data and so used
to assess the ability of global chemical models to
reproduce this important atmospheric region.
As an example, the relation between CO and O3 (C)
measured in the UTLS tropics (A - red/pink) and
subtropics (top - pale/dark blue) during the pre-AVE
and AVE campaigns shows anomalous behaviour
in the subtropics (A - orange). The particle
analysis of the origins of these measurements (D)
(B) shows that they are drawn from two distinct
regions, the lower subtropical troposphere and the
extratropical lower stratosphere.
The particle-based methods have also allowed
mapping of transport pathways showing the strong
latitudinal and longitudinal structure of surface
regions that act as a source for the stratosphere. (D) and enters the stratosphere after ascent from
For example, air that enters the stratosphere the outflow from these storms. This information is
in mid- and high latitudes originates from the now being used to estimate the stratospheric ozone
surface in mid-latitude oceanic regions (C) and depletion that is likely to result from emission of
ascends in the warm conveyor belt of weather bromine compounds at different geographical
systems, whereas air that enters the stratosphere locations.
in the subtropics originates from the surface in the
regions of deepest convective storms in the tropics
35
Objective 10:
Interest • specific developments of applied CCMs to
improve the agreement with observations; and
Reliable assessment of the future evolution of
stratospheric ozone and the consequential impact • use of improved CCMs for new simulations
on surface ultraviolet (UV) irradiance requires a to provide the best estimates for assessments
good understanding of the relevant atmospheric of temporal evolution of ozone, climate and
processes. Chemistry-climate models (CCMs) are surface UV irradiance.
the principal tool used to make such assessments,
and they are central to determining whether the
regulation of ozone depleting substances (ODSs) Findings
by the Montreal Protocol is sufficient to fully
restore the stratospheric ozone layer in future. Ten CCMs were used for the first time in an extensive
The increasing impact of climate change means set of coordinated, multi-year simulations. These
that the evolution of the ozone layer in the next provided the basis for the projections of the future
few decades will not be a simple reversal of past evolution of the ozone layer in the UNEP/WMO
changes, and understanding the coupling between Scientific Assessment of Ozone Depletion: 2006.
climate change and stratospheric ozone depletion
is the central aim in SCOUT-O3.
Approach
Observations in combination with atmospheric
models were used to investigate recent changes
of climate, atmospheric composition (especially
ozone) and surface UV irradiance. The aim is
to describe and better understand the critical
processes of the Earth’s atmosphere as well as
the feedback mechanisms influencing short- and
long-term changes. In particular, coupled CCMs
considering the interaction of physical, dynamical
and chemical processes are used to reproduce
observed fluctuations and trends as well as to
perform prognostic studies to assess possible
future evolution of climate, ozone and surface UV
irradiance.
Scientific studies during SCOUT-O3 can be
divided into three main overlapping phases: Early in SCOUT-O3, detailed comparisons
revealed obvious differences in the predictions of
• evaluation of the performance of CCMs by ozone, climate, and UV derived from the various
comparison of CCM results with each other CCMs. Model calculations have been intensively
and with observations to identify strengths and tested with relevant observations. In particular,
weaknesses of the applied numerical models; comparisons with the new measurements taken
during the SCOUT-O3 tropical campaigns have
36
Predictions of Ozone Recovery and Surface UV
been used to analyse the altitude distribution and • surface UV irradiance is expected to decrease
variability of chemical species and the influence due to the anticipated global recovery of
of convection. As a consequence, improvements stratospheric ozone, surface UV irradiance is
were made to a number of individual CCMs. expected to decrease. However climate change
will also influence surface UV irradiance
Near the end of SCOUT-O3 a multitude of through changes induced mainly on clouds
improved CCMs has been used to carry out new and surface reflectivity. This could result in
multi-year simulations, covering the period from a future increase of surface UV irradiance,
1960 to 2100. These results have been provided depending on geographical region and season.
to and further investigated for the SPARC
CCMVal report (to be published in early 2010),
the upcoming UNEP/WMO Scientific Assessment
of Ozone Depletion: 2010, and Fifth Assessment
Report of the IPCC. So far the major results are:
• CCMs indicate that future increases of
greenhouse gas concentrations will contribute
to a further cooling in the stratosphere;
• Chemical reaction rates in the atmosphere
cre dependent on temperature and thus
ozone concentrations are sensitive to climate
Impact on CCMs and More Generally
changes;
Within SCOUT-O3, CCMs have improved
• greenhouse gas induced changes of significantly. The intensive evaluation of model
stratospheric temperature and dynamics are data with respective observations has enabled
expected to accelerate the increase of total modelling groups to identify obvious deficiencies
global ozone in the next decades. Ozone layer in model systems applied so far. This has led to
recovery develops differently in different a purposeful development of CCMs. Currently
atmospheric regions and climate change is available CCMs are still far from being “perfect”
affecting it. The ozone layer’s recreation is not model systems describing observed changes in
a simple reversal of recent development, e.g. all details, but they have made a big step towards
decreasing stratospheric temperature in high more reliable predictions in the last five years.
latitude regions could lead to a slow down of
the closure of the Antarctic ozone hole;
• a full recovery of the ozone layer is expected
around the middle of this century and there is
a chance for an ozone “super-recovery”, i.e.
future levels of stratospheric ozone may be
higher than in the first half of the last century.
A typical example for achieved results shows
calculations of column ozone (60°N to 60°S)
from one model for the period 1960-2050
compared to two satellite measurements; and
37
The World Avoided by the Montreal Protocol
The Effect of the Montreal Protocol gases, and it was recently demonstrated that the
Montreal Protocol has had a major, beneficial
From the 1960s onwards, there was a rapid climate impact; as in its absence the radiative
rise in the manufacture and use of a number of forcing just by ozone-depleting substances would
halogenated (mainly chlorine- but also bromine- already have been comparable to that from CO2.
based) compounds which had a wide range of Without the Protocol we would effectively be
industrial and domestic uses. Concerns about their about a decade further into climate change; the
environmental impacts began in the 1970s and the Protocol has brought precious time further drastic
demonstration of their role in the rapid Antarctic reductions of other greenhouse gases.
springtime polar depletion in the 1980s led to
regulation (phase-out) of these ozone-depleting
substances under the Montreal Protocol. The
benefits of the Montreal Protocol for atmospheric What did the Montreal Protocol Achieve?
halogen abundances can be seen in the box. The
original Protocol made a modest impact, slowing In SCOUT-O3 we have asked questions such as:
down the rate at which these compounds entered What ozone depletion, and surface UV increase,
the atmosphere, but subsequent amendments have has been avoided by the Protocol? Ozone is a
led to a trajectory where the atmosphere is slowly climate gas, so that the avoided ozone depletion
being cleansed of these industrial halogens. will also have avoided some climate change. How
large is this avoided change?
It is interesting to ask what would have happened
if the Montreal Protocol had not been enacted and
if the much higher emissions of ozone-depleting
substances had occurred. One important aspect is
that the ozone-depleting substances are greenhouse
The Montreal Protocol aimed to achieve reductions
in stratospheric abundances of chlorine and
bromine through restrictions on the production
and consumption of manufactured halogen source
gases. Projections of the future halogen amounts
are shown assuming 1) no Protocol regulations, 2)
only the regulations in the original 1987 Montreal
Protocol, and 3) subsequent changes to the Protocol
(labelled by where and when changes to the original
1987 Protocol provisions were agreed). Without the
Protocol, stratospheric halogen gases were projected
to increase significantly in the 21st century. The
“zero emissions” line shows a hypothetical case
of stratospheric abundances if all emissions were
reduced to zero beginning in 2007.
38
Avoided Modification of Climate
Without the Protocol the abundance of halogen
species in the atmosphere could have reached
9 part per billion by 2030. A calculation
with one of the chemistry-climate models in
SCOUT-O3 shows that this increase in the halogens
would have led to further large ozone destruction,
reaching locally to perhaps 40% in both the upper and
lower stratosphere. Changes in stratospheric ozone
have an impact on surface temperatures by influencing
the transmission of solar and infrared radiation through
the atmosphere. The changes in surface temperatures
have a complex spatial pattern (reminiscent in the
Antarctic of observed changes attributed to the ozone
hole) and are large in magnitude.
Avoided Skin Cancers
The large calculated reductions in ozone lead to a large calculated increase in UV (assuming that
cloudiness remains the same) with a consequent impact on human health. This has been assessed in
SCOUT-O3. Models have been used to estimate the global distribution of skin cancer cases avoided
by the Montreal Protocol. The estimate is very large; bearing in mind the possible caveats in the
extrapolation to human health, it is clear that the Montreal protocol has been enormously beneficial for
the human population.
39
Future Directions for Stratospheric Research
Stratospheric science has reached a new, mature phase. In the 25 years since the discovery of the ‘Ozone
Hole’ we have established the basic understanding of the processes behind Antarctic ozone loss. EU-funded
research during the 1990s has demonstrated that these processes also occur in the Arctic and can affect
populated middle latitudes. Within SCOUT-O3, this understanding has been incorporated into climate
models which have been used to address the issue of stratospheric ozone recovery and the impact on surface
UV. While our understanding has advanced significantly it would be a mistake to think that the science is
now settled (just as it would be wrong to think that our understanding of climate change is complete). More
appropriately, stratospheric science should now be seen to be a central component of Earth System Science.
We will not be able to make improved projections about global change unless we improve our understanding
of how the stratosphere couples into the whole system.
A future research strategy needs to have two components. First, there are still fundamental issues relating to
the stratospheric science. The UTLS region and the tropical tropopause layer are likely to remain key foci;
changes here have biggest impact on, e.g., tropospheric chemistry and surface climate. Questions include:
• the need to improve our understanding of the processes controlling radiatively active components (O3,
water vapour, aerosols) in the cold UTLS;
• quantitative understanding of troposphere to stratosphere exchange in the tropics, including the role
of deep convection, and extratropical stratosphere to troposphere exchange and how these will change
under climate change;
• the role of biogenically emitted very short lived halogen substances in the future;
• the role of growing anthropogenic emission of source gases (e.g methane, nitrous oxide and pollution in
the tropics)
• the role of volcanic emissions and solar variations in ozone recovery.
Secondly, we need to understand quantitatively how changes in the stratosphere impact the whole climate
system. Questions include:
• the role of lower stratospheric ozone for regional climate change;
• how the stratosphere circulation couples to important modes of climate variability, including the North
Atlantic Oscillation, El Nino and the monsoon circulation;
• the importance of lower stratosphere for seasonal weather forecasting;
• the importance of lower stratospheric ozone, and its changes, for tropospheric chemistry and surface
UV radiation; and
• how geoengineering of the lower stratosphere could impact surface climate and chemistry of the
stratosphere.
In addition, research on UV radiation needs to be more closely integrated with studies of climate change
and tropospheric composition changes as clouds and tropospheric aerosols are likely to be major factors in
determining future UV radiation at the Earth’s surface.
40
Data Policy and Database
General Policy Nadir Database
SCOUT-O3 is a complex project involving many A major role for the Nadir data centre throughout
sorts of measurements and model calculations the project is the provision of ancillary information
which had to be integrated to achieve the scientific such as meteorological analyses and ozone maps.
aims. Accordingly a clear data policy was The atmospheric context is valuable in interpreting
developed which included support for two central the atmospheric measurements and so these were
databases in addition to those maintained by many supplied routinely for the analysis of data from
individual partners. These were the Nadir data SCOUT-O3 itself as well as in studies of previously
centre at NILU which already stores atmospheric existing measurements. Two newsletters were
data from many European projects and field published highlighting the new and existing
measurement campaigns, and the European products available at the Nadir database.
Database for UV Climatology and Evaluation at
FMI which is the main European repository for Several tropical field campaigns were organised
UV measurements. A SCOUT-O3 committee within SCOUT-O3 to investigate the mechanisms
monitored the effectiveness of the data policy and by which air passes from the upper troposphere to
suggested new developments. the lower stratosphere. A field database was set up
European Database for
UV Climatology and Evaluation
The European Database for UV Climatology and
Evaluation has been developed in projects in the
EC’s 4th and 5th Framework Programmes. The
database serves the UV scientist community in
SCOUT-O3, but also reaches out to wider research
communities working on ozone, human health,
and terrestrial and aquatic ecosystems, and various
multi disciplinary research areas. Currently the
database holds over 2.8 million spectra measured in Darwin for the airborne campaign which took
at 38 stations in 16 European countries. place in late 2005 in order to support the flight
planning. Special directories were set up for all
the SCOUT-O3 field campaigns in order to provide
easy access for post-campaign analysis.
The data from all the field measurement campaigns
(N. Australia, W. Africa and S. America) are stored
on Nadir. In order to interpret and understand
the small scale feature in a long-term and global
context, satellite measurements (e.g. from
ENVISAT and CALIPSO), measurements from
ground-based instruments and other global fields
will be used in conjunction with models from
regional to global scales.
41
Dissemination, Outreach
General contributed well over 500 talks and posters at
international conferences and meetings including
those of the European Geophysical Union and
Scientific research takes place in a broad context
the American Geophysical Union. These papers
and so an important aspect of SCOUT-O3 has
and presentations relate to the many individual
been to disseminate the project’s scientific results
research projects which take place within such a
to a wide audience: other scientists (specialists and
large enterprise as SCOUT-O3, and of which only
non-specialists), policy-makers and the public.
a flavour can be given in this summary. SCOUT-
This has been in the form of:
O3 scientists have also written articles for a more
• scientific journals and meetings; general scientific audience in, for example, SPARC
newsletter and magazines published by their own
• international scientific assessments; and institutions or funding agencies.
• press and public events.
Training the scientists of tomorrow
In addition SCOUT-O3 scientists help train
the scientists of tomorrow and have actively A major research project like SCOUT-O3 provides
participated in programmes to promote science as an excellent way of involving young scientists in
a career for women. an international setting. Nearly 40 PhD students
have been reported as working directly on SCOUT-
O3-related projects and many more will have been
Scientific Discussions involved at some level or other. Many early career
post-doctoral researchers have also taken part.
Researchers have written or contributed to over 350 The international context is important because it
peer-reviewed papers (with more in the pipeline) in exposes the young scientists to many groups and
over 50 international scientific journals, including cultures and so lets them build up their own sets of
Science, Atmospheric Chemistry and Physics and contacts and colleagues at an early stage.
the Journal of Geophysical Research. They have
42
and Human Capital
International Assessments O3 suggests that such actions are most effective
as the institutions are responsible for their own
A sound scientific understanding is a necessary hiring, promoting and employment policies, and
(though not sufficient) criterion for making the have the best links with their local and national
right decisions on global environmental problems communities as well as the best understanding of
such as ozone depletion and climate change, the cultural issues they are dealing with
and SCOUT-O3 was designed to provide this.
In addition to providing important scientific
information in the form of peer-reviewed papers, Informing the public
SCOUT-O3 scientists have been personally
involved as contributors, authors or lead authors Reaching out to a wider audience is important
with international Scientific Assessments. to maintain the public interest and knowledge
Most notable are the UNEP/WMO Scientific of science. With this motivation, SCOUT-O3
Assessments of Ozone Depletion in 2006 and scientists have given many talks at schools and
2010, and there were also significant contributions within their local communities throughout the
to the IPCC Special Report Safeguarding the world. They have also been involved in public
Ozone Layer and the Global Climate System, the outreach events aimed at making science more
IPCC Fourth Assessment Report, UNEP’s GEO-4 accessible to the public as well as encouraging
report and the EEA’s State of the Environment and children to become more interested in learning
Outlook report 2010. science at university.
There has been much international press interest
throughout the project which SCOUT-O3 scientists
have responded to. The field measurements
campaigns in West Africa, North Australia and
South America all received a lot of attention from
the local and international press.
Encouraging female scientists
SCOUT-O3, like all EC Integrated Projects,
had a gender action plan which particularly
concentrated on ensuring that within SCOUT-O3
female scientists had equal opportunities when
issues such as positions of responsibility, talks,
etc. were considered. In addition many scientists
were actively involved in initiatives run by their
own institutions. The experience in SCOUT-
43
Ozone loss at both poles receives a fair amount
of attention, and in 2005 SCOUT-O3 issued press
updates about the large ozone losses in the Arctic
that year. This received a great deal of attention,
particularly in Europe and Canada. SCOUT-
O3 scientists have been asked to comment on
atmospheric science related articles/items on
television, radio, newspapers and internet. Overall
media coverage including television documentaries
and reports, radio programmes and articles in
newspaper and popular science magazines.
44
45
List of Organisations Involved with SCOUT-O3
Name Country Name Country
University of Cambridge United Kingdom Observatory of Neuchâtel Switzerland
Alfred Wegener Institute Germany Paul Scherrer Institute Switzerland
Belgisch Instituut voor Ruimte- National Institute for Public Health
Aëronomie Belgium and Environment The Netherlands
Central Aerological Observatory Russia Royal Netherlands Meteorological
Centre National de Recherches Institute The Netherlands
Scientifique France Sveriges Meteorologiska och
Chalmers University of Technology Sweden Hydrologiska Institut Sweden
Chemical Research Center Hungary Stratosphere-M, Ltd Russia
Consiglio Nazionale delle Ricerche Italy University of Bern Switzerland
Czech Hydrometeorological Institute Czech Republic University of Bremen Germany
Danish Meteorological Institute Denmark University of Buenos Aires Argentina
Physical Meteorology Observatory University of Crete Greece
of Davos Switzerland Johann Wolfgang Goethe
Demokritus University of Thrace Greece University of Frankfurt Germany
Deutsches Zentrum für Luft University of Göteborg Sweden
und Raumfahrt Germany University of Hannover Germany
Deutscher WetterDienst Lindenberg University of Heidelberg Germany
Germany Medizinische Universität Innsbruck Austria
Ente per le Nuove Tecnologie, University of Karlsruhe Germany
L’Energia e l’Ambiente Italy
University of Lancaster United Kingdom
ETH Zürich Switzerland
University of L’Aquila Italy
Finnish Meteorological Institute Finland
University of Leeds United Kingdom
Free University of Berlin Germany
University of Leicester United Kingdom
Forschungszentrum Jülich GmBH Germany
University of Oslo Norway
Forschungszentrum Karlsruhe GmBH Germany
Aristotle University of Thessaloniki Greece
Imperial College of Science,
Technology and Medicine United Kingdom University of Wyoming USA
Instituto Nacional de Técnica University of California at Irvine USA
Aeroespacial Spain UK Met Office United Kingdom
Istituto Nazionale di Geofisicae University of East Anglia United Kingdom
Vulcanologia Italy
Universitaet für Bodenkultur Austria
Istituto Nazionale di Ottica Applicata Italy
Weather Informatics United Kingdom
Johannes-Gutenberg Universitat Mainz Germany
Chemical Processing Research Institute Greece
Karl-Franzens-Universitaet Graz Austria
Pontif. Univ. Cat. Argentina St Maria
Max Planck Gesellschaft Germany de los Buenos Aires Argentina
Météo France France University of Utrecht The Netherlands
National and Kapodistrian University of Manchester United Kingdom
University of Athens Greece
University of Bielefeld Germany
Norwegian Institute for Air Research Norway
University of Wuppertal Germany
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