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Reports on the EGS’02 General Assembly
Nice, France, April 21-26, 2002
Session A20 - Tropospheric Chemistry and Aerosols
Convenor: Christian George, CNRS-LACE, France (Christian.George@univ-lyon1.fr)
Co-Conveners: M. Ammann, T. Hoffmann, T. Koop, and F. Dentener
In an overview lecture on the aerosol formation in the free troposphere
by F. Arnold, special attention was given to aircraft and laboratory measurements
of ionic and gaseous aerosol precursors for which our current understanding is poor. Following talks dealt also with aerosol
formation and covered a large range of conditions through field observations (i.e., from aircraft exhausts to nucleation over
forest or oceans) or laboratory experiments (e.g., oxidation of toluene) or modelling.
Also of interest were the properties of particles such as hygroscopicity, deliquescence and efflorescence points as well
as the thermodynamics of the associated changes. For example, the thermodynamic behaviour of single suspended
H2SO4/NH3/H2O-particles was presented for different stoichiometries
at different temperatures and relative humidities suggesting that a new, hitherto unknown phase is observed during the
experiments (then identified as ammonium bisulfate monohydrate).
E. Vignati showed that an efficient and accurate representation of aerosol size
distributions and microphysical processes is required to make physically consistent calculations of the direct and indirect
radiative effects of aerosols and their impact on climate. This was made through an overview of recent developments of
aerosol modelling (global and regional), outlining the advantages and disadvantages of the various techniques for such large scales,
which were also highlighted in following talks.
M. Canagaratna then started an overview on the use of aerosol mass spectrometry (AMS),
which provides real-time information on size resolved aerosol mass loading for volatile and semi-volatile molecular components.
Such an AMS has now been deployed in field studies in 10 locations worldwide, recording aerosol size and composition with time
resolution of minutes, showing for example that inorganic (sulfate) loading tends to dominate large “accumulation” mode
loading while “organics” dominate smaller (100-200nm) particles. The following studies dealt with chemistry on
aerosols (liquid or solid) highlighting the complementary between such an approach and field chemical analysis of particles,
which underlines, among other the role of organics.
J. Donaldson (invited) studied the uptake of water onto organic films containing oxidised
functional groups. In fact, surface oxidation of atmospheric particles containing significant mass fractions of organic compounds
is expected to alter the hydrophobic nature of an organic surface layer, and thus perhaps facilitate the particle’s ability
to act as a cloud condensation nucleus. He highlighted some results for the room-temperature condensation of water onto films
composed of aliphatic hydrocarbons, mono- and di-alcohols and mono- and di-acids. Surface oxidation, through radicals, was also
highlighted in another presentation where it was studied directly by means of time resolved the diffuse reflectance coupled to flash
laser photolysis. A set of presentations showed different modelling studies of the chemistry in aqueous droplets or on mineral
aerosols during ACE campaigns.
In a lively poster session, all of the above mentioned topics were again highlighted by many high quality contributions.
Session ST3 – Open Session on the middle at phere: dynamics and chemistry
Converner: Martin Juckes, SSTD Oxfordshire, UK (M.N.Juckes@rl.ac.uk)
Co-Conveners: E. Manzini, and R. Müller
M. Chipperfield opened the session with an invited talk on 3-D modelling of stratospheric
chemistry. His model was able to capture trends and variability well, and attributed most of the mid-latitude ozone trend of around
-5%/decade to halogens. L. Callis concluded from a 2-D isentropic model that variations in
transport associated with variations in temperature around the stratopause level were responsible for ozone variability in the 1980s.
An analysis of the data record for the temperature variability was presented by F. Schmidlin.
H.-M. Steinhorst analysed the effect of mixing between air parcels in a Lagrangian chemical
model. Th. Reddmann looked at the effect of combining a prognostic dynamical model in the upper
stratosphere with ERA 15 analyses in the lower stratosphere to obtain dynamical fields with greater consistency to drive a
chemical model. This approach improved the performance of the chemical model.
M. Giorgetta (invited review) noted that modelled QBOs tend to be less robust than the
atmospheric phenomenon. The effects of varying vertical and horizontal resolutions and varying convective parameterisations
were discussed.
T. Roeckmann described balloon measurements of the anomalous oxygen isotope ratio
in stratospheric carbon dioxide, which cannot be explained by gravitational fractionation. He proposed a chemical fractionation
process involving an ozone reaction with an isotope dependant reaction rate.
S. Griffiths
described how non-linear scale selection might account for the vertical and meridional scales of equatorial inertial instability.
In an invited talk B. Boville reviewed work with the NCAR Whole Atmosphere Community
Climate Model (from ground to 140km). Gravity wave (GW) drag becomes dominant above 1 hPa. A correlation between El Niño
and stratospheric temperatures was found, but the realism of this was questioned in the light of the model's inability to reproduce the QBO.
The response to El Niño begins at the tropical stratopause and then moves polewards and downwards. The mesospheric temperatures
are sensitive to details of the GW drag parameterisation.
V. Fomichev from doubled CO2 experiments with the Canadian Middle
Atmosphere Model found a warming of 3K in the troposphere and a 10K cooling in the stratosphere. A 10% increase on stratospheric
ozone was found.
A. Kutepov described the development of a heterodyne IR spectrometer to measure species
abundances, kinetic temperature, non-LTE effects and local winds in the middle atmosphere. The method relies on the ability to resolve
individual spectral line shapes.
S. Kirkwood analysed the relation between noctilucent cloud occurence (at 85km) and wave
activity (stationary and 5 day) extrapolated from 55km UKMO analyses. It was concluded that meridional advection associated with the
waves was a significant factor in the formation of the clouds.
J. Scinocca described an accurate spectral non-orographic GW drag parameterisation:
an adaption of the Warner-McIntyre scheme, with efficiency gains achieved by integrating over the intrinsic frequency. This makes
the scheme efficient enough for use in a GCM. K. Stebel presented a climatology of GW propagation
from 5 years of MST radar (ESRAD) data. In the troposphere there was equipartition between kinetic and potential energy, and also
between upward and downward propagating waves. In the stratosphere, kinetic energy was 40% greater than potential energy,
and upward propagation was dominant. R. Plougonven described GW generation near jets in the
FASTEX campaign using, inter alia, data from high resolution radiosoundings. Large amplitude wave events generally coincided either
with a jet maximum or a jet break.
In an invited talk K. Kodera found that the dynamical response of the stratosphere to the solar
cycle was more than direct thermal forcing can explain. He suggested that modulation of internal variability associated with planetary
wave propagation might be a factor. A model intercomparison produced variable response to fluctuations in solar forcing.
B. Christiansen gave an invited talk on the downward propagation of the Arctic Oscillation.
He proposed a QBO style model, based on a Holton and Mass formulation, to explain the observed downwards phase propagation.
R. Müller described a generalisation of Lait's potential vorticity (itself a modification of
Ertel's potential vorticity with reduced density dependence) aimed to facilitate intercomparison of PV maps at different heights.
S. Sparrow described some idealised experiments investigating the link between equatorial winds
and polar stratospheric warmings. A clear modulation of the warming frequency was found, though there was substantial internal variability
when the imposed equatorial winds were weak. The warmings tended to start at the subtropical stratopause and then move polewards and
downwards. Travelling anticyclones appear to play a role in the lead up to the warmings. H. Heinrich
investigated the non-linear forcing of stratospheric planetary waves using a Duffing equation and CEOF analyses of ERA15 data. The stratosphere
was found to lag the troposphere by 4.5 days. T. Halenka used NCEP reanalyses to investigate the
relation between solar activity and global circulation patterns. M. Sigmond investigated correlations
between meridional wind in the stratosphere and zonal wind in the troposphere. He found the stratosphere leading the troposphere by about
one day.
S. Yoden presented results from a 3-D mechanistic model of the troposphere and stratosphere, forced
with 1km zonal wavenumber 1 orography. Stratospheric warmings were found to occur randomly in time, matching a Poisson process. A 1K
cooling of the polar troposphere during easterly phases of the QBO was found.
In the Poster Session, P. Braesicke described the ASAD chemistry package developed for use
with the UK Met Office Unified Model. B. Naujokat intercompared 6 operational meteorological
analyses; the differences are large enough to have a significant influence on chemical models they may be used to drive.
I. Fedulina analysed travelling planetary waves using UKMO assimilated stratospheric data.
Differences between the hemispheres were consistent with the stronger westerly vortex in the southern winter.
C. Cagnazzo studied equatorial waves using TOVS temperatures.
C. Piani documented the way in which winds in the polar middle atmosphere lock into solid body
rotation in early June every year. M. Juckes described the diabatic circulation associated with the
disturbed winter polar stratospheric vortex, and the apparent diabatic ascent diagnosed from ERA15 data.
Ch. Jacobi found from radar data, that a mesospheric wind reversal accompanied the stratospheric warming
in February 2001.
C.-F. Enell used ground-based photographs to study PSCs. Interesting new results concerning
the intrinsic frequency spectra of stratospheric air motions were obtained by A. Hertzog from
constant density balloons.
B. Deuber described a new instrument for ground-based measurement of middle atmospheric
water vapour. T. Schroder used GPS occultation measurements to retrieve temperature and water
vapour profiles.
Session ST4 - Atmospheric Ozone (co-sponsored by OA Section)
Converner: Peter Fabian, University of Munich, Germany (fabian@met.forst.uni-muenchen.de)
Co-Convener: M. M. Hirschberg.
This year’s subsession on Global Ozone comprised 11 oral and 11 poster presentations.
Highlights were water vapour and ozone fields computed with ERA-40 as compared with MOZAIC results (
E.K. Oikonomou and A. O’Neill), ozone and temperature fields derived from
CHRISTA measurements (I. Galkina,
G. Kruchenitsky and S. Perov) and 3 exciting new Umkehr applications presented
in the poster session by O.V. Postyliakov et al., B. Rajewska-Wiech
and M. Degorska.
P. Braesicke and J.A. Pyle showed interesting applications of the
Cambridge Unified Model, M. Bourqui and K.P. Shine of the Reading
Intermediate GCM, both investigating ozone loss, B.M. Sinnhuber et al. elucidated the role of bromine
in stratospheric ozone depletion, and H.P. Haase et al. discussed the variability of various trace
gases based on balloon and satellite data.
It should be noted that while the tropospheric ozone issues belong to OA, the stratosphere is part of the ST Section. This structure has now
been changed, and both the troposphere and the middle atmosphere are embedded in the new Atmospheric Section; it is already implemented and
will be effective for the 2003 Assembly.
Session ST8 - Chemistry-Climate Interaction
Convener: Martin Dameris, Institute of Atmospheric Physics, Wessling, Germany (martin.dameris@dlr.de)
This session had only 9 contributions (6 oral presentations), but the interest for the session was very high. More than 120 visitors listened
to the oral presentations and it would have been even more if the meeting room would have been larger.
C. Schnadt gave an invited talk discussing the main results of an inter-comparison project, where
currently available chemistry-climate models have been evaluated with observations and analyses. The results of specific diagnostics were
analysed to examine the differences amongst individual models and observations, to assess the consistency of model predictions, with
a particular focus on polar ozone. Many models indicate a clear cold bias in high latitudes, in particular in the Southern Hemisphere during
winter and spring. It seems that the problem can be reduced with the use of non-orographic gravity wave drag schemes. The model results
were also compared to assess the possible future behaviour of ozone. The different models indicate that ozone depletion may worsen but
thereafter give a range of results concerning timing and extent of ozone recovery. The Antarctic ozone recovery could begin any year within
the range 2001 to 2008. Due to larger uncertainties, which originate in the dynamic variability of the Northern Hemisphere, for the Arctic
the recovery is expected within the range 2004 to 2019.
M. Dameris pointed out that there are indications from some (chemistry-)climate model simulations
that the future polar stratosphere in the Northern Hemisphere will be warmer during late winter and early spring than in recent times.
Combined with decreasing chlorine concentrations in the stratosphere this would yield an accelerated recovery of the ozone layer to values
observed in the 1980s within less than two decades. However, other models show the expected general cooling of the lower stratosphere
in all seasons, which is caused by the radiative feedback of enhanced greenhouse gas concentrations and its intensification by ozone depletion
in the spring season. It is still an open question whether the warming of the northern polar lower stratosphere is an artefact of specific models
or if it could be a possible behaviour of the future stratosphere due to mutual effects. In his presentation analyses of ECHAM4.L39(DLR)/CHEM
model simulations were presented and discussed with respect to dynamic processes, which yield the simulated warming in this coupled
chemistry-climate model. It turned out that an increase of the stationary wave activity is responsible for this model behaviour.
The activity of the transient waves did not change in the distinct model scenarios.
Results of a Middle Atmosphere version of ECHAM/CHEM were presented by C. Brühl.
He discussed multi-year model simulations with fixed boundary conditions for past, current and future conditions. Calculated changes
in chemical and dynamical values seem to be in fair agreement with observations, for example results from the HALOE instrument.
G. Pitari employed a low-resolution chemistry-climate model, which considers an on-line inclusion
of a micro-physical code for aerosol formation and growth. Therefore, volcanic perturbations of stratospheric aerosol can be taken into account.
First preliminary results were presented of long-term runs, which were compared with TOMS and SAGE data.
Results of the NCAR CCM climate model were presented by I. Isaksen, where they have included
atmospheric chemical processes. He pointed out that the distribution and changes of active greenhouse gases (ozone and methane) and
secondary particles (sulphate) in the troposphere are strongly affected by atmospheric oxidation involving precursors like NOx and
CO, NMHC and oxidants like O3, OH, and H2O2. In order to obtain a realistic representation of the
chemistry-climate interaction in coupled models, the global emissions and distribution of the precursors and the formation and distribution
of the secondary key gases need to be accurately represented in the models.
Employing the Unified Model, the cause and effect of mid-latitude ozone loss and associated changes in dynamics have been analysed
by J. Pyle and co-workers. Therefore, the model has been run in conjunction with a simplified chemistry
module. Based on a series of simulations he concluded that about 50% of the mid-latitude ozone changes originate from dynamics.
In general, it was an exciting session. Investigations with respect to mutual effects of dynamical, physical and chemical effect will significantly
increase in near future. Questions about future changes of chemical composition of the atmosphere and its effect on climate and vice versa are
raised in nearly all current announcements of atmospheric programmes. Not only the timing of the recovery of the ozone layer is of common
interest. Therefore, it is planned to continue with this session during the following EGS meetings.
For further information check the web site: http://www.copernicus.org/EGS/egsga/nice02/nice02.htm
