Impact of UTLS including Tropical Tropopause Layer (TTL) on Stratosphere
Preferred Presentation: oral

Ozone production and loss in the UTLS region

Isaksen, Ivar; Gauss, Michael

Chemical and dynamical processes
Analysis of results from modelling and observations

A global 3-D CTM (the Oslo CTM2)with extensive tropospheric chemistry (including hydrocarbon reactions)and stratospheric chemistry (including chlorine and bromine reactions)is used to study ozone production and loss processes in the UTLS region. A microphysics module is included to account for heteoregenous processes in the lower stratosphere. The model includes emission of ozone precursors from natural and pollution sources at the surface (including biomass burning), free tropospheric NOx production from lightning, and stratospheric production of NOx from N2O oxidation. The Oslo CTM2 uses off-line pre-calculated meteorlogical and physical data from the European Centre of Medium Range Weather Forecasts (ECMWF).The model is run for selected years and model output is compaared with observations. Multiyear runs are performed. Based on the model runs extensive model/model comparisons and model/measurement comparisons have been performed (Gauss et al., 2003a; Gauss et al.,2003b; Brunner et al., 2003). Processes affecting ozone, ozone precursor distribution and ozone loss processes at middle and high northern latitudes are studied in particular. Ozone, NOx, CO and CFC distribution in the UTLS region are compared with observations. Ozone loss in the lower stratosphere due to the impact of heterogenous processes, as well as ozone production from hydrocarbons, CO and methane oxidation in the upper troposphere and lowermost part of the stratosphere is analysed. It is particular important to analyse processes at heights where there is a change from ozone production to ozone loss, since this changeover is sensitive both to the chemical and dynamical parimeterizations. Furthermore, cross tropopause fluxes of ozone are estimated. These fluxes are resulting from the calculated ozone production and loss in the stratosphere.
 
 

References
 
 

Brunner, D., J. Staehelin, H. Rogers, M. Koehler, J. Pyle, D. Hauglustaine, L. Jourdain, T.K. Berntsen, M. Gauss, I.S.A. Isaksen, E. Meijer, P. van Velthoven, G. Pitari, E. Mancini, V. Grewe and R. Sausen: An evaluation of the performance of chemistry transport models by comparison with scientific aircraft observations. Part 1: Concepts and overall model performance over four distinct regions, Atmos. Chem. Phys., Atmos., 3, 2499-2545, 2003.
 
 

Gauss, M., I.S.A. Isaksen, S. Wong, and W.-C. Wang: The impact of H2O emissions from kerosene aircraft and cryoplanes on the atmosphere. Accepted for publication in J. Geophys. Res., 2003a.
 
 

Gauss, M., G. Myhre, G. Pitari, M. J. Prather, I. S. A. Isaksen, T. K. Berntsen, G. P. Brasseur, F. J. Dentener, R. G. Derwent, D. A. Hauglustaine, L. W. Horowitz, D. J. Jacob, M. Johnson, K. S. Law, L. J. Mickley, J.-F. Müller, P.-H. Plantevin, J. A. Pyle, H. L. Rogers, D. S. Stevenson, J. K. Sundet, M. van Weele, O. Wild, Radiative forcing in the 21st century due to ozone changes in the troposphere and the lower stratosphere. Accepted for publication in J. Geophys. Res., 2003b.
 
 
 
 


Impact of UTLS including Tropical Tropopause Layer (TTL) on Stratosphere
Preferred Presentation: poster

A climatology of the northern hemisphere winter tropopause in comparison of ECMWF analyses and the DLR/E39C general circulation model

Kouker, Wolfgang; Reddmann, Thomas; Ruhnke, Roland; Schnadt, Christine; Dameris, Martin

Analyses of the Tropopause
Quantitative triangulation scheme

A new scheme that enables a quantitative investigation of complex structured surfaces is developed based on the triangulation of the space. A first application is applied to the climatological structure of the tropopause which is defined here as a combination of the 2 PVU Ertel.s Potential Vorticity surface and the 380 K potential temperature surface in the tropics.
 
 

In this study the Karlsruhe Simulation model of the Middle Atmosphere (KASIMA) model is applied by nudging the ECMWF analysed temperature to the solution of a prognostic primitive equation model to compute the tropopause structure based on the ECMWF analyses of the years 1979-1998 and compared with data of a 20 year 1990 timeslice experiment performed with the DLR E39/C Chemistry Climate Model.
 
 

As expected the seasonal mean of the tropopause (TP) height derived from KASIMA has a rather steep gradient in subtropical regions where the jet streams develop. The E39C model does reproduce this feature in the overall but the gradient is not as steep as in KASIMA. The variability of the TP-height peaks in both models in the region of the steep gradient with a considerable larger variability in the E39C model. Additionally, the relative size of the tropopause per unit horizontal surface, which becomes large in cases of steep gradients and tropopause folding events will be compared.
 
 
 
 


Impact of UTLS including Tropical Tropopause Layer (TTL) on Stratosphere
Preferred Presentation: oral

Characterstic changes in water and cloud through the TTL

MacKenzie, A. R.; Schiller, C., FZJ, Germany Ren, C., Lancaster University, UK Rohs, S., FZJ, Germany

Cirrus clouds and dehydration
Characterstic changes in water and cloud through the TTL

In-situ measurements of water and cloud properties in the tropical tropopause region are sparse, making the definition of diagnostic relationships, particularly time-dependent relationships, difficult. Nevertheless, the importance of the tropical tropopause in determining the composition of the stratosphere justifies attempts to provide even provisional diagnostics.

 Here we describe measurements of water vapour, total water, relative humidity, and cirrus cloud properties from the APE-THESEO mission of February-March 1999. We supplement these observations with Lagrangian cirrus model results, to provide provisional descriptions of the characteristic changes in water-related quantities through the tropopause transition layer (TTL). A relatively simple, physically based, cirrus parameterisation, driven by ECMWF ERA40 analyses, represents APE-THESEO data, and a satellite data sample, with reasonable faithfulness. The parameterisation is suitable for use in coupled chemistry-climate models.
 
 
 
 


Impact of UTLS including Tropical Tropopause Layer (TTL) on Stratosphere
Preferred Presentation: oral

Evaluation of the transport characteristics in extratropical UTLS in the NCAR Whole Atmosphere Community Climate Model (WACCM)

Pan, Laura; Jennifer Wei, Douglas Kinnison, Jean-Francois Lamarque, Rolando Garcia, and Byron Boville

Stratosphere-Troposphere Exchange; Transport characteristic in the vicinity of the extratropical tropopause
Representations of the extratropical tropopause and the seasonal variation of STE

We have performed a model evaluation for the representations of the extratropical UTLS region using observed tracer relationships. The main objective of the analyses is to examine how well the transport processes, especially the processes in the vicinity of the subtropical jet, are represented in the model. The O3-CO relationship in the UTLS region from aircraft measurements is used to evaluate the WACCM2. Analyses of the in-situ measurements have shown that the O3-CO mixing ratios in the extratropical UTLS region form a compact, L-shaped correlation [Fischer et al. 2000; Zahn et al., 2000; Hoor et al., 2002]. The formation and maintenance of the two branches in the L are due to the source/sink distributions of the two tracers and the difference in the stratosphere and troposphere circulations. The data analyses have also shown the transition between the two branches occurs at the tropopause [Pan et al., 2003]. Using these relationships, we show that the model correctly positions the tropopause in tracer space and represents well the latitudinal dependence of the mixing characteristics. In addition, analysis of the model results revealed the cyclone-anticyclone asymmetry of the dynamical tropopause with respect to thermal tropopause, consistent with a previous theoretical study [Wirth, JAS, 2001]. Furthermore, the model tracer correlation indicates that the depression of the dynamical tropopause on the cyclonic side is associated with irreversible stratosphere to troposphere transport.

 References Fischer, H., F. G. Wienhold, P. Hoor, O. Bujok, C. Schiller, P. Siegmund, M. Ambaum, H. A. Scheeren, and J. Lelieveld, Tracer correlations in the northern high latitude lowermost stratosphere: Influence of cross-tropopause mass exchange, Geophys. Res. Lett., 27, 97100, 2000.

 Hoor, P., H. Fischer, L. Lange, J. Lelieveld, and D. Brunner, Seasonal variations of a mixing layer in the lowermost stratosphere as identified by the CO-O3 correlation from in situ measurements, J. Geophys. Res., 107(D5), 4044, doi:10.1029/2000JD000289, 2002.

 Pan, L. L., W. J. Randel, E. Browell, B. J. Gary, M. J. Mahoney, and E. J. Hintsa, Definitions and the Sharpness of the Extratropical Tropopause: A Trace Gas Perspective, to be submitted to JGR, 2003.

 Zahn, A., et al., Identification of extratropical two-way troposphere-stratosphere mixing based on CARIBIC measurements of O3, CO, and ultrafine particles, J. Geophys. Res., 105, 15271535, 2000.
 
 


Impact of UTLS including Tropical Tropopause Layer (TTL) on Stratosphere
Preferred Presentation: oral

Using the Tropopause Height for Model Evaluation and Detection of Climate Change

Sausen, Robert; Santer, B.D.; Wigley, T.M.L.; Taylor, K.E.; Boyle, J.S.; Brüggemann, W.; Meehl, G.A.; Roeckner, E.; Dameris, M.; Schnadt, C.; Eyring, V.; Grewe, V.; Ponater, M.




The height of the global-mean tropopause shows a steady increase since 1979 in ?re-analyses? of numerical weather forecasts. This is in agreement with results from a climate model driven by natural and anthropogenic forcings. Superimposed on the multi-decadal overall trends in both simulations and re-analyses are higher-frequency fluctuations related to explosive vol-canic eruptions. Global-mean tropopause height has the desirable property of acting as a natu-ral filter, removing much of the El Niño/Southern Oscillation (ENSO) variability that ham-pers the interpretation of tropospheric temperature changes. Monitoring tropopause height may therefore facilitate the separation of ENSO- and volcanically-induced variability from anthropogenic effects. At the same time comparing modelled tropopause height with ob-servered data present a kind a integrative test of the quality of a climate model. In model ex-periments with anthropogenic influences, changes in tropopause height have a higher signal-to-noise ratio than changes in surface temperature, and can be detected roughly 20 years ear-lier. In transient experminet with a climate-chemistry model the impact of chemistry on the tropopause can additionally be studied.
 
 


Radiative Transfer and Balance
Preferred Presentation:

Interactive photolysis rate calculations in th GCM ECHAM, comparisons with observations near the surface

Brühl, Christoph

Photolysis rates, solar radiation and clouds
variability, wavelength dependence

Results from a fast interactive radiative transfer scheme for calculation of actinic fluxes and photolysis rates in the GCM ECHAM, considering clouds and overhead ozone, will be presented. It is shown that the calculated range of photolysis rates for different species near the surface agrees well with measurements based on a spectroradiometer during the BERLIOZ-campaign in July/August 1998.

 References:

 Junkermann et al, J. Atmosph. Chem. 42, 413-441, 2002.

 Steil et al, J. Geophys. Res., 108, D9, 4290, doi:10.1029/2002JD002971, 2003.

 Landgraf, J. and P.J. Crutzen, J. Atmosph. Sci., 55, 863-878, 1998.
 
 


Radiative Transfer and Balance
Preferred Presentation: poster

PFCs and UTLS temperatures

Forster, Piers

raditive heating
temperature

What is the direct radiative effect of CFC replacements on UTLS temperatures?

I don't know but I will by November!
 
 


Radiative Transfer and Balance
Preferred Presentation: oral

The Radiation Balance of the Tropical Tropopause Layer

Gettelman, Andrew; Forster, Piers Fu, Qiang Fujiwara, Masatomo

Radiation Balance of the Tropopause Region
Intercomparison of Model Radiation Codes and Sensitivities

The radiation balance of the tropical tropopause layer is examined in detail using several different radiation codes. These codes include detailed radiative transfer models and parameterized or simplified codes for coupled chemistry-climate models. The radiation models are compared using standard profiles compiled from observations in the tropics. The various gases of importance in the upper troposphere and lower stratosphere are examined. The importance of the various radiatively active gases are examined. Water vapor is found to be the most important contributor to the radiation balance, but carbon dioxide and ozone may also play an important role. The sensitivity of the radiation balance and the level of zero clear sky radiative heating, important for the transport of constituents into the stratosphere, is also explored. Differences and similarities between the models will be discussed, with the implications for the stratosphere addressed.
 
 


Radiative Transfer and Balance
Preferred Presentation: oral

Clouds and actinic Flux - first results of INSPECTRO

Scheirer, Ronald; Mayer, Bernhard




Photochemical processes are driven by ultraviolet (UV) radiation, in particular, the spherically integrated radiance or actinic flux. The abundance and spectral distribution of UV actinic flux in turn is strongly modulated by the atmospheric composition itself, in particular, by clouds which are highly variable in space and time. The EU project INSPECTRO (INfluence of clouds on the SPECtral actinic flux in the lower TROposphere) aims at gaining a quantitative understanding of the relationship between clouds and the actinic flux. In September 2002 a first field campaign in Norwich, East Anglia took place. Photochemical relevant radiation as well as cloud microphysics, and aerosol and chemical constituents were simultaneously measured by three airplanes, an ultra-light aircraft, a hot-air balloon, and four ground stations. This data set forms probably the most complete data base available to date for the validation of actinic flux parameterisations throughout the troposphere. In this presentation first results from the campaign will be shown to demonstrate the role of clouds in tropospheric chemistry.
 
 


Radiative Transfer and Balance
Preferred Presentation: poster

A comparison of model-simulated trends in stratospheric temperatures

Shine, Keith; Forster, Piers + lots more

Climate Change
Temperature

Estimates of annual-mean stratospheric temperature trends over the past twenty years, from a wide variety of models, are compared both with each other and with the observed cooling seen in trend analyses using radiosonde and satellite observations.

The modelled temperature trends are driven by changes in ozone (either imposed from observations or calculated by the model), carbon dioxide and other relatively well-mixed greenhouse gases, and stratospheric water vapour. The comparison shows that whilst models generally simulate similar patterns in the vertical profile of annual-and global-mean temperature trends, there is a significant divergence in the size of the modelled trends, even when similar trace gas perturbations are imposed. Coupled-chemistry models are in as good agreement as models using imposed observed ozone trends, despite the extra degree of freedom that the coupled models possess.

The modelled annual- and global-mean cooling of the upper stratosphere (near 1 hPa) is dominated by ozone and carbon dioxide changes, and is in reasonable agreement with observations. At about 5 hPa, the mean cooling from the models is systematically greater than that seen in the satellite data; however, for some models, depending on the size of the temperature trend due to stratospheric water vapour changes, the uncertainty estimates of the model and observations just overlap. Near 10 hPa there is good agreement with observations. In the lower stratosphere (20-70 hPa), ozone appears to be the dominant contributor to the observed cooling, although it does not, on its own, seem to explain the entire cooling.

Annual- and zonal-mean temperature trends at 100 hPa and 50 hPa are also examined. At 100 hPa, the modelled cooling due to ozone depletion alone is in reasonable agreement with the observed cooling at all latitudes. At 50 hPa, however, the observed cooling at midlatitudes of the northern hemisphere significantly exceeds the modelled cooling due to ozone depletion alone. There is an indication of a similar effect in high northern latitudes, but the greater variability in both models and observations precludes a firm conclusion.

The discrepancies between modelled and observed temperature trends in the lower stratosphere are reduced if the cooling effects of increased stratospheric water vapour concentration are included, and could be largely removed if certain assumptions were made regarding the size and distribution of the water vapour increase. However, given the uncertainties in the geographical extent of water vapour changes in the lower stratosphere, and the time period over which such changes have been sustained, other reasons for the discrepancy between modelled and observed temperature trends cannot be ruled out.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

The interactive chemistry climate model MAECHAM4-CHEM, longterm simulations for near past, present and near future.

Bruehl, Christoph; Steil, Benedikt; Manzini, Elisa

Polar chemical ozone loss
Interannual variability for sixties, present and near future

Results of eight 20-year time-slice experiments with the chemistry-climate model MA-ECHAM4-CHEM for typical boundary conditions from 1960 to 2030 are presented. To separate effects, for 1990

 3 different sea-surface temperature data sets were selected, for 2000 2 different stratospheric chlorine concentrations, and for 2030 a scenario which considers the stratospheric cooling by enhanced CO_2 only, and a scenario where all boundary conditions are changed.

 We focus on ozone depletion and chlorine partitioning in the lower stratosphere in high latitude spring, including interannual variability and comparisons with observations.

References: Steil et al, J.Geophys.Res. 108, D9, 4290, 2003.

 Manzini et al, J.Geophys.Res. 108, D14, 4429, 2003.
 
 
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Polar stratospheric cloud simulations with ECHAM 5

Buchholz, Joachim; Meilinger, Stefanie Lelieveld, Jos

process
diagnostic

A polar stratospheric cloud (PSC) module has been developed for the coupled troposphere-stratosphere chemistry-climate model ECHAM 5. Microphysical processes that lead to the formation of supercooled ternary solutions (STS), nitric acid trihydrate (NAT), and ice particles in the polar stratosphere are modelled as well as heterogeneous chemical reactions of halogenes and dinitrogen pentoxide on liquid and solid aerosol particles. Denitrification and dehydration due to sedimenting solid PSC particles are calculated for each grid box depending on particle size, pressure and temperature. This poster presents first results of PSC simulations with ECHAM 5.
 
 



Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Atmospheric Chemistry in the Community Atmosphere Model

Philip Cameron-Smith (LLNL), Doug Rotman (LLNL),  Jean-Francois Lamarque (NCAR), Stacy Walters (NCAR), John Taylor (ANL), Peter Gleckler (LLNL)

process
diagnostic



We are adding a fast atmospheric chemistry mechanism to the U.S. National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM2) as part of the U.S. Department of Energy (DOE) Scientific Discovery through Advanced Computing program (SciDAC). The mechanism covers the primary chemical processes in the troposphere and
stratosphere. We are also developing a new methane emission dataset so that methane can be interactive in the model.

We plan to validate the chemistry in the combined model by comparing chemical concentrations of ozone and its precursors with: an offline chemistry transport model (the Lawrence Livermore National Lab. IMPACT model), surface sites, ozonesondes, aircraft campaigns, and satellite observations.
We plan to validate the GCM response by performing simulations with and without chemistry that adhere to the standard experimental protocol of the Atmospheric Model Intercomparison Project (AMIP).  AMIP simulations are constrained by observed monthly mean sea-surface temperatures and sea-ice, starting in 1979 and run to near-present.  Extensive diagnostic tests will be performed on these runs using diagnostic tools developed by the Program for Climate Model Diagnosis and Intercomparison (PCMDI).

This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.


Stratospheric Chemistry and Aerosols
Preferred Presentation: oral

Quantification of the importance of denitrification in a future stratosphere

Carslaw, Ken; Davies, Stewart Mann, Graham Chipperfield, Martyn

Denitrification
Stratospheric HNO3 measurements

Denitrificatin is known to increase ozone loss in a typical cold Arctic winter, and the magntude of the increased loss depends on the precise meteorological conditions. In this paper we assess the factors that control denitrification and how it could change in a stratosphere with different meteorology. We look at the importance of several meteorological quantities: (i) the minimum temperature; (ii) the area of the cold pool; (iii) the colocatio of the cold pool and the vortex; (iv) the depth of the cold pool. We show the relative importance of each of these variables in controlling the current rate of denitrification in the Arctic stratosphere and assess whether their relative importance changes in a different stratosphere. Finally, we assess the potential for increasing the denitrification-induced ozone loss in a different stratosphere.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Chemistry Climate interactions after large volcanic eruptions I

Graf Hans_F.; Timmreck Claudia Li, Qian Thomas Manu Anna

Continental winter warming after tropical volcanic eruption
Refractive Indices, EP FLUX, Divergence of EP Flux

Major volcanic eruptions have a significant impact on stratospheric and tropospheric climate, chemical composition and circulation. CCM model simulations allow to integrate these data and to derive estimates of the sensitivity of the climate system to different compounds of the disturbance. This should be tested for the period following the eruption of Mt. Pinatubo. Several in-situ and remote sensing measurements have detected the dispersal of the Pinatubo cloud and the following changes in the atmospheric system (temperature, trace gas concentration). A monthly mean data set of observed Pinatubo aerosol forcing exist (PADS) (Stenchikov et al, 1998), which is also used in the SPARc GRIPS Iniative PINMIP. At least five indepent realizations should be performed with each Chemistry-Climate Model with the PADS dat set and with observed SST for two years after the eruption. The model should reproduce continental winter warming
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Lagrangian CTM studies of future polar vortex structure and ozone loss

Lemmen, Carsten; Guenther, Gebhard; Mager, Fabian; Dameris, Martin; Riese, Martin; Mueller, Rolf

Chemical ozone loss
Lagrangian CTM calculations on GCM meteorology; Tracer-tracer correlation

Indications of Antarctic ozone hole recovery are expected by all major General Circulation Models (GCM) before 2010, whereas the start of Arctic ozone hole recovery is much more uncertain and predicted somewhere between 2004 and 2019. Among features of a future Arctic climate are a colder and more humid polar stratosphere, possibly delaying amelioration of ozone depletion expected due to reduced chlorine loading. To assess the sensitivity of (a) Arctic winter ozone loss and (b) spring transport of ozone-depleted air into midlatitudes to a changing future climate we employ the Chemical Lagrangian Model of the Stratosphere (CLaMS) based on meteorological and chemical boundary conditions from 20- year ECHAM4.L39(DLR)/CHEM timeslice experiments. Box model chemistry including bromine and heterogeneous reactions on PSCs is calculated along multiple trajectories, mixing of air parcels is driven by wind shear and strain. The formation and evolution of filaments, where the small-scale variability of chemical constituents is believed to have a significant effect on ozone loss, is realistically simulated; extrusions of ozone-depleted air masses from the vortex into midlatitudes are conserved for several days. Chemically induced changes in ozone concentrations are followed by using an inert ozone tracer and are also independently derived from tracer-tracer correlations. Detailed chemistry simulations for a scenario 1990 cold winter show an accumulated ozone loss of more than 1 ppm; in the GCM simulation, accumulated ozone depletion is significantly lower due to underestimated chlorine loading.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Impact of climate and emission changes on stratospheric sulphuric acid aerosols

Pitari, Giovanni; Mancini, Eva

Mid-latitude Chemical Ozone Loss
Chemical Ozone Loss versus Potential SSA-SAD

Recent investigations have shown that stratospheric ozone loss is mainly driven by polar processes, and that the actual amount of polar, mid-latitude and global ozone trends is dependent on polar temperatures, PSC formation and Cl/Br radical species formation and persistence in both polar vortices. Troposphere-stratosphere are coupled in such a way that GHG forced changes in climate may effectively feedback on stratospheric dynamics, thus affecting ozone transport and chemistry, primarily via polar heterogeneous losses. However, this is not the only possible strat/trop dynamical interaction with a potential significant impact on stratospheric ozone: water vapour trends at the tropical tropopause is an

example of another critical effect that needs further investigation.

Here it is suggested that sulphuric acid aerosols in the lower stratosphere may be affected by future climate and emission changes. In-situ measurements recently collected at the tropical tropopause give a best estimate of the sulphate mixing ratio of 0.258 ppbv, with 0.049 ppbv standard deviation (SPARC assessment on stratospheric aerosols, in preparation). This value is sensitive to the amount of SO2 which is moved to the tropical tropopause via deep convection, and it might change with future trends of global and regional

emissions of SO2, as well as with increasing convective mass fluxes. In the work of Pitari et al. (2002) only the effects of changing sulphur emissions were taken into account in the balance of SO2 at the tropical tropopause, but nevertheless the impact on the surface area density of sulphuric acid aerosols (SSA-SAD) in the lower stratosphere was found to be non-negligible, as well as on mid-latitude ozone losses.
 
 

REFERENCE: Pitari, G., E. Mancini, V. Rizi, and D.T. Shindell: Impact of future climate and emission changes on stratospheric aerosols and ozone, J. Atmos. Sci., 59, 414-440, 2002.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: oral

An approach to diagnose polar ozone loss in CCM calculations

Rex, Markus; Eyring, V.,Dameris, M., Grewe, V., Schnadt, C.

polar ozone loss
chemical ozone loss versus PSC formation potential

The total column amount of ozone at high latitutdes in spring is largely governed by two processes during the preceding winter: the strength of the residual circulation and the degree of chemical loss. For the ability of CCMs to predict future Arctic ozone levels in a scenario of changing climate and recovering halogen levels, a correct representation of both effects under current climate conditions is crucial. Validation approaches that focus on validating the total ozone column and its standard deviation may be misleading, since biases in the representation of the two mechanisms can easily cancel. We have developed an approach to validate the ability of CCMs to represent the observed degree of chemical ozone loss during Arctic winter. The approach is based on an empirical relation between the overall degree of chemical loss and a temperature based parameter that represents the PSC formation potential of a given winter. Results from validating the chemical loss of ozone in the coupled chemistry-climate model ECHAM4(DLR)/CHEM will be presented.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Validation of a nudged 3-D circulation model including full stratospheric chemistry with satellite data

Ruhnke, Roland; Reddmann, Thomas; Kouker, Wolfgang

Seasonal and long-term distributions, age of air
Correlations, age of air

The validation of Chemistry-Climate-Models (CCMs) and Chemistry-Transport-Models (CTMs) is essential for the reliability of the prediction or diagnosis of the processes involved. Satellite measurements with global coverage can be used to validate these global models which have to be forced by meteorological analyses of the wind and temperature fields to be in agreement with the actual state of the atmosphere being measured by the satellite instruments.
 
 

In this study, a nudged ERA-40 long-term simulation has been performed with the Karlsruhe Simulation model of the Middle Atmosphere (KASIMA) with full stratospheric chemistry to simulate the long-term behaviour of the stratosphere. The model results of the stratospheric species (e.g. O3, HNO3, N2O, CH4) are validated with satellite measurements with respect to their long-term and seasonal distribution. As a measure of quality for the long-term behaviour of model run the age of air will be investigated. Correlations with satellite measurements will be used to validate the seasonal distribution of the stratospheric species revealing the usefullness and limitations of those studies.
 
 
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

The solar cycle variation of chemical species in the middle atmosphere studied with a 3-D chemistry-climate model

SEKIYAMA, Thomas; SHIBATA, Kiyotaka; DEUSHI, Makoto; ORITO, Kohtaro; KODERA, Kunihiko

Solar cycle variation
Solar cycle variation of chemical species

Photochemical reactions in the atmosphere are induced by ultraviolet (UV) radiation from the sun. Radiation from the sun shows an 11-year oscillation, in which total irradiance changes are relatively small. But more than 10 % irradiance changes occur in ultraviolet (UV) radiation. The photochemical reactions, therefore, are influenced by the solar cycle variation. The response of the stratospheric ozone particularly could have an impact on Earth?s climate. We have analyzed the results of a three-dimensional chemistry-climate model of the Meteorological Research Institute (MRI) in order to evaluate the sensitivity of chemical species in the stratosphere and mesosphere to the solar cycle variation.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: oral

Stratospheric Bromine Chemistry

Sinnhuber, Bjoern-Martin; Sinnhuber, Miriam

Stratospheric Bromine Chemistry
Alpha-factor; Modeled versus Measured BrO

Bromine plays an important role in stratospheric ozone depletion. In the past, many chemistry climate models have not included bromine chemistry explicitely, but instead used the Effective Equivalent Stratospheric Chlorine (EESC) loading. This assumes that the relative importance of bromine relative to chlorine can be described by a constant factor (alpha-factor). Here we present model calculations showing that the local alpha-factor is much larger in the lowermost stratosphere than the column averaged alpha-factor generally used in EESC. Validation of the modeled bromine chemistry in a chemistry climate model could be performed along two lines: (a) a comparison of the alpha-factor with models including full stratospheric chemistry and (b) direct comparison with BrO observations.

 REFERENCE:

 Sinnhuber, B.-M., et al., Comparison of measurements and model calculations of stratospheric bromine monoxide, J. Geophys. Res., 107, 10.1029/2001JD000940, 2002.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Evaluation of stratospheric temperature fidelity using an NCEP climatology

Strahan, Susan; Douglass, Anne

Temperature-dependent gas phase stratospheric chemistry
Distribution of the difference between model and climatological most probable temperatures

Many gas and heterogeneous phase chemical reactions depend on temperature, but different tests are required to evaluate model temperature behavior with respect to these types of reactions. For evaluation of gas phase reactions, we compare how often and how closely model temperatures agree with climatological values. National Center for Environmental Prediction (NCEP) temperature analyses from 1980-1999 provide the basis for this stratospheric temperature test. Daily, area-weighted temperature distributions are calculated for 11 latitude bands and 8 pressure levels from 150-1 mb with this 20 yr data set. Climatological monthly mean distributions are then calculated from the 20 years of daily distributions. The test itself examines the difference between the model and climatological most probable temperature (MPT) for each month and latitude band, resulting in 132 points of comparison on each of 8 pressure surfaces in one year. The results of this comparison are easily visualized. A latitude vs. month contour plot on each pressure level reveals spatial or season patterns in the differences. The probability distribution function (pdf) of the differences on each pressure level illustrates biases as a function of height.
 
 
 
 
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: oral

Changes in southern hemisphere NO2: Comparison of measurements and model results

Struthers, Hamish; Austin, John Bodeker, Greg Kreher, Karin

Mid-latitude ozone loss
Changes in NOy partitioning

At Lauder, New Zealand (45S, 169E), it has been established that the rate of increase of NO2 over the past 20 years is more than 5% per decade, significantly greater than it's major source N2O, which has increased at approximately 3% per decade over the same time period (Liley et al. 2000). This suggests there has been a change in partitioning of NOy over Lauder during the past 20 years.

 Future predictions of mid-latitude ozone change show catalytic NOx ozone loss cycles becoming increasingly important in the middle stratosphere (20km-35km) as NOx levels increase over the next century (Randeniya et al. 2002). Any shift in the partitioning of NOy to more NOx is likely to exacerbate ozone loss via NOx catalytic cycles.

 Modelling studies show the rate of increase of NO2 is influenced by the rate of increase in N2O but also changes in ozone, temperature, transport, halogen amounts and aerosol changes (McLinden et al. 2001, Fish et al. 2000). Thus, any prediction of future NO2 requires the use of a fully coupled, chemical/dynamical model.

 We calculate NO2 slant column densities (scd) using output from the UMETRAC CCM (Austin, 2002) and compare the resulting timeseries with measured scd's from NIWA's sites at Lauder and Arrival Heights (77.5S, 165E), to validate the NOx chemistry in the model. Non-linear least squares regression analysis of the timeseries is used to derive the secular trends. Analysis of the measured timeseries includes treatment of El Chichon and Pinatubo volcanoes, ENSO, solar cycle and QBO.

 From this analysis, we argue that an index of NOy partitioning is useful for validating CCM's and is an important indicator of CCM's ability to predict future mid-latitude ozone changes.

 Liley, J. B., Johnston, P. B., McKenzie, R. L., Thomas, A. J. and Boyd, I. S. Stratospheric NO2 variations from a long time series at Lauder, New Zealand. J. Geophys. Res. 105 (D9), p 11633-11640, 2000.

 Randeniya, L. K., Vohralik, P. F. and Plumb, I. C. Stratospheric ozone depletion at northern mid latitudes in the 21st century. The importance of future concentrations of greenhouse gases nitrous oxide and methane. Geophys. Res. Lett. 29, 10.1029/2001GL014295, 2002.

 McLinden, C. A., Olsen, S. C., Prather, M. J. and Liley, J. B. Understanding trends in stratospheric NOy and NO2. J. Geophys. Res. 106 (D21), p 27787-27793, 2001.

 Fish, D. J., Roscoe, H. K. and Johnston, P. V. Possible causes of stratospheric NO2 trends observed at Lauder, New Zealand. Geophys. Res. Lett. 27, p 3313-3316, 2000.

 Austin, J. A three-dimensional coupled chemistry-climate model simulation of past stratospheric trends. J. Atmos. Sci., 59 (2), p 218-232, 2002.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Simulation of Pinatubo aerosols and its impact on stratospheric chemistry by using a CCSR/NIES AGCM

TAKIGAWA, Masayuki; TAKAHASHI, Masaaki; AKIYOSHI, Hideharu;

Pinatubo aerosols
Chemical and radiative effect of Pinatubo aerosols

A new middle-atmosphere general circulation model that includes the photochemistry for Ox-HOx-NOx-ClOx-SOx species has been constructed. Heterogeneous reaction on the sulfate aerosol are being considered in the model. The dynamical, radiative, chemical processes of the model are fully coupled. That is, the concentrations of the chemical species in the chemical process and the radiative flux in the radiation process mutually interact in the model. The model is based on version 5.4 of the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) AGCM, and the chemical process predicts the concentrations of 37 chemically reactive gases, and includes 26 photolysis, 71 homogeneous reactions. It also includes 4 heterogeneous reactions on the surface of sulfate aerosols. The impact of the sulfate aerosol on the climate after the eruption of Mt. Pinatubo, is estimated. The focus of this study is to estimate the chemical and radiative influence of the volcanic aerosol. For this purpose, one standard experiments and two Pinatubo experiments are investigated. We assume an initial volcanic cloud mass of 17 TgS, as a Gaussian distribution centered at 25km. In the horizontal the Pinatubo cloud is initialized between 0-19.4N and 96E-118E, corresponding with TOMS observations of June 16, 1991. In EXP1, only background aerosol is considered. EXP2 and EXP 3 are prepared for the simulation of Mt. Pinatubo eruption, and the difference of EXP2 and EXP3 is the treatment of heterogeneous reactions on sulfate aerosols. The radiative effect, i.e., longwave absorption and shortwave scattering, is taken into account in both of EXP2 and EXP3. The model is able to reproduce the temperature increase in the lower stratosphere by the longwave absorption of sulfate aerosol. The warming caused by the volcanic eruption in the lower stratosphere has the maximum value of about 1-2K for EXP2 (with heterogeneous reactions on sulfate aerosol), and about 2-3K for EXP3 (without heterogeneous reactions). By considering the heterogeneous reaction on the volcanic aerosol, overestimation of the warming disappears. In EXP2, a rapid decrease of the heating by shortwave absorption appears since October 1991. This structure is caused by the ozone depletion by the enhancement the cloud mass of 17 TgS, as a Gaussian distribution centered at 25km. In the horizontal the Pinatubo cloud is initialized between 0-19.4N and 96E-118E, corresponding with TOMS observations of June 16, 1991. In EXP1, only background aerosol is considered. EXP2 and EXP 3 are prepared for the simulation of Mt. Pinatubo eruption, and the difference of EXP2 and EXP3 is the treatment of heterogeneous reactions on sulfate aerosols. The radiative effect, i.e., longwave absorption and shortwave scattering, is taken into account in both of EXP2 and EXP3. The model is able to reproduce the temperature increase in the lower stratosphere by the longwave absorption of sulfate aerosol. The warming caused by the volcanic eruption in the lower stratosphere has the maximum value of about 1-2K for EXP2 (with heterogeneous reactions on sulfate aerosol), and about 2-3K for EXP3 (without heterogeneous reactions). By considering the heterogeneous reaction on the volcanic aerosol, overestimation of the warming disappears. In EXP2, a rapid decrease of the heating by shortwave absorption appears since October 1991. This structure is caused by the ozone depletion by the enhancement the ozone destruction by ClOx. Ozone also absorbs longwave, and corresponding weakening of longwave cooling can be seen.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

The effects of non-orographic GWD scheme and radiation from large SZA on the Antarctic ozone hole

Tatsuya, Nagashima; Masaaki, Takahashi Hideharu, Akiyoshi Masayuki, Takigawa

Antarctic ozone hole

Antarctic ozone hole is the most prominent phenomenon in the stratospheric chemistry, and it should be reasonably represented in every CCM. The Antarctic ozone hole simulated in several CCM, including ours, however, have some problems. As to our CCM, the causes of such problems are manifold. The stronger polar vortex in connection with the polar cold bias problem in the Southern Hemisphere in our CCM can cause a delay of the seasonal march of the simulated Antarctic ozone hole. It also causes an insufficient downward transport of Cly species down to the lower stratosphere in the polar vortex, which weaken the ozone destruction by ClOx species. Neglect of the solar incidence from large solar zenith angle (SZA) can bring weak ozone destruction at the beginning of the Antarctic ozone hole (August and September).

In order to eliminate such problems from our CCM, a non-orographic gravity wave grad (GWD) parameterization were included and the effect of solar incidence from the SZA larger than 90 degree was considered. The latter can advance the beginning of ozone destruction in the Antarctic region. The influence of GWD parameterization on the stratospheric ozone is highly dependent on the employed parameter setting, and we are now seeking the optimum setting to improve the seasonal march of the Antarctic ozone hole.
 
 
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: oral

Effects of stratospheric water vapour on O3 depletion: A coupled chemistry-climate model study

Tian Wenshou; Chipperfield Martyn

process
diagnostic

A detailed and successfully used chemical transport model (SLIMCAT) is coupled to the Met Office Unified Model (UM) to study the interaction between stratospheric chemical processes and climate changes. The resulting model has 28 chemical tracers with around 42 chemical species including the Ox, HOx, Cly, Bry, and NOy families. The heterogeneous chemistry is considered and the model chemical fields of H2O, O3 and GHGs are coupled to the UM's radiation scheme. The coupled model is stable and efficient. The comparisons between observations and the model results indicate that the coupled model performs quite well and gives reasonable outputs.

 The model has been run with and without the coupling effects of assumed increases in stratospheric H2O on the model's radiation and/or chemistry scheme. We will discuss the calculations of future polar O3 depletion in terms of recovery and diagnose the dominant factors in determining the impact of future H2O increases.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation: poster

Chemistry Climate interactions after large volcanic eruptions II

Timmreck, Claudia

Stratospheric transport (transport,through subtropical barrier, STE,cross-equatorial transport)
Mass flux through tropopause and / well defined pressure levels, liftetime of cloud

The volcanic eruption of Mt. Pinatubo,in June 1991, had not only significant impact on stratospheric and tropospheric climate and circulation, it is also a natural phenomenonwhich enables us to better understand stratospheric tranport processes, especially in the tropical region. For the Pinatubo period (1991 -1993) a large amount of observations exist, which offer a unique opportunity to verify and to test the representation of the subtropical barrierrof STE and of 3d transport in the CCM. A well defined inert stratospherc volcanic tracer should be implemented in the tropical stratosphere around 30 hPa similar to the initial Pinatubo cloud. In the tropopshere an e-folding time should be assumed.
 
 


Stratospheric Chemistry and Aerosols
Preferred Presentation:

A new treatment of PSCs for Chemistry-Climate Models

van den Broek, Miranda; Bregman, Bram

denitrification
CTM treatment of denitrification

One of the major uncertainties in climate - stratospheric ozone chemistry feedbacks is the crude representation of denitrification by polar stratospheric clouds (PSCs) in chemistry-climate models. Here we present an algorithm that treats NAT PSC particles as transported species, based on the parameterization of Carslaw et al. [2002]. The code takes into account NAT particle growth, evaporation and sedimentation. It has been made suitable for Eulerian Chemistry-Climate models and we have implemented the algorithm in our 3D Chemistry-Transport Model TM5. PSC particles are transported within a number of sizebins.

We focused on the 1999/2000 Arctic winter. The results for NAT and HNO3 have been compared with a reference lagrangian model and with airborne observations. We have investigated how the PSC representation in the lower Arctic stratosphere depends on several key parameters, such as the number of size bins, particle density and model resolution.
 
 

Carslaw, K.S., J.A. Kettleborough, M.J. Northway, S. Davies, R.S. Gao, D.W. Fahey, D.G. Baumgardner, M.P. Chipperfield, and A. Kleinböhl, A vortex-scale simulation of the growth and sedimentation of large nitric acid hydrate particles, J. Geophys. Res., 107, D20, 8300, doi:10.1029/2001JD000467, 2002
 
 
 
 


Stratospheric Dynamics
Preferred Presentation: poster

Sensitivity of dynamics and ozone to different representations of SSTs in the Unified Model

Braesicke, Peter; Pyle, John A.

Vortex dynamics/NH midwinter warmings
Correlations between circulation indices

We use a version of the Met Office Unified Model with a simple stratospheric chemistry to perform a set of multi-annual integrations of 20 years each. The runs have different representations of ozone in the radiation and prescribed SSTs. In one experiment the same long-term mean monthly mean SSTs are used each model year, whereas all other experiments use annual varying AMIP~II monthly mean SSTs instead. All runs have the same simplified ozone chemistry included (regardless of which ozone is used in the radiation), therefore we can estimate the impact of dynamical changes on ozone. We contrast the sensitivity of the model system towards the representation of ozone with the changes associated with the removal of the inter-annual variability in SSTs. We show that the appearance of extreme events in the northern hemisphere winter stratosphere as modelled with the Unified Model is linked more to the representation of SSTs than it is to ozone.
 
 


Stratospheric Dynamics
Preferred Presentation: poster

Cold bias and its sensitivity to the dissipation scheme

Burkhardt, Ulrike; Becker, Erich

Dissipative heating
hemispheric + global dissipation rates as estimated from the energy cycle

The cold temperature bias in the polar lower stratosphere is still a common problem of climate models. This temperature error has an impact on the simulation of the height of the tropopause and on the simulated distributions of moisture and ozone.

 A new dissipative heating scheme has recently been suggested by Becker (2003). The scheme has been tested in a simplified model and the resulting dissipation has been found to agree with estimates of the long-term global mean dissipation. The new dissipation has now been implemented in the ECHAM model. It consists of a dissipation due to vertical diffusion and a dissipation due to horizontal diffusion of kinetic energy. The latter has maximum values in the lower stratosphere in mid latitudes, resulting in a reduction of the cold temperature bias in the lower stratosphere.

 Dissipation rates will be compared to estimates of the observed dissipation made, for example, by Peixoto and Ort, and the resulting change in circulation will be presented.
 
 


Stratospheric Dynamics
Preferred Presentation: oral

Comparison of zonal large scale ozone variability derived from ECHAM4.L39(DLR)/CHEM and TOMS total ozone data

Erbertseder, Thilo; Eyring, Veronika Bittner, Michael Dameris, Martin

Dynamic induced ozone variability in lower stratosphere
Hemispheric Ozone Variability Indices

Total Ozone Mapping Spectrometer (TOMS) total ozone data from 1978 to 2002 and corresponding ozone fields of the coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM are analysed in order to derive and compare zonal large scale ozone variations. Emphasis is on seasonal variations of the zonal wave numbers one and two, which are interpreted as the manifestation of the quasi-stationary planetary waves number one and two.

The dynamics of the middle atmosphere is characterized by manifold processes on different temporal and spatial scales. The total ozone column can be considered as a tracer to illuminate and investigate the dynamics of the middle atmosphere. Since the main contribution of the total ozone column stems mainly from the height region between 15 to 30 km and ozone can be regarded there as chemical conservative on short time scales, the spatial distribution and variability of the ozone column is mainly controlled by the dominating dynamical processes in the lower stratosphere that are planetary waves.
 
 

To compare the ozone variablity of the CCM and the satellite borne observations, the horizontal zonal amplitudes and phases are derived by means of spectral statistical analysis. These results are used to derive two hemispheric Ozone Variability Indices which are defined as the hemispheric mean of the zonal amplitude of the planetary waves number 1 and 2, respectively.
 
 

We present a comparison of time series of the parameters and address the differences. A wavelet analysis completes the study by presenting the time scales of total ozone variability of the CCM and the observations.
 
 

References:

 Bittner, M and 17 co-authors: Long period / large scale oscillations of temperature during the DYANA campaign. Journal of Atm. Terr. Phys 56, 1675-1700 (1994)

 Bittner, M, Dech, S, Loyola, D: Planetary scale waves in total ozone from ERS-2 GOME data. Proc 3rd ERS Symp. on Space at the service of our Environment, Florence, Italy, March (1997)

 Erbertseder, T., Bittner, M.: Long period variability of middle atmosphere dynamics. Ozone Bulletin of the German Weather Service, No 62 (1999)

 Erbertseder, T, Baier, F. and Bittner, M, Exceptional early breakup of the Antarctic ozone hole. Ozone Bulletin of the German Weather Service, No 89, October (2002)
 
 


Stratospheric Dynamics
Preferred Presentation: poster

Modelling the QBO effects on tracer distributions

Giorgetta, Marco A.

dynamical mixing between tropics and extratropics
age of air, position and strength of the transport barrier defined by PV

Chemistry-climate models are powerful tools to test our understanding of the variations in circulation and composition of the middle atmosphere. Models used so far usually are unable to simulate the quasi-biennial oscillation (QBO), and hence show significant differences in the circulation and composition of the stratosphere, not only in the tropics but also in the extratropics, when compared to observations. This work investigates the role of the QBO in the dynamical mixing of tropical and extratropical air masses, as it can be studied with passiv tracers similar to SF6, and by evaluation of the age of air, in a GCM that simulates the QBO. Passive tracers are released in experiments based on the MAECHAM5.2 GCM in versions with high and standard vertical resolution , with and without simulation of the QBO, respectively. QBO effects on the age of air and on the position and strength of the subtropical mixing barrier are estimated by a comparison of these experiments.
 
 


Stratospheric Dynamics
Preferred Presentation: oral

Climate Change in a Stratospheric Mechanistic Model

Hampson, John; Bekki, Slimane Hauchecorne, Alain Keckhut, Philippe Chanin, Marie-Lise

Temperature and ozone trends in the stratosphere due to changes in greenhouse gas forcing.
Trend analysis multi-parameter fit model (AMOUNTS)

As part of the European Community project EuroSPICE, Service d'Aéronomie have carried out two model runs using the stratospheric dynamical-chemistry model MSDOL. The model is forced at the tropopause by using greenhouse gas (CFCs, N2O, CH4, CO2) values, for one model run using observed values from 1980-2000 and for the second run using predicted values for 2000-2020.
 
 

The model results are analysed for trends in the temperature and ozone, as well as any other changes in the model dynamics. In particular, trends are calculated using a multi-parameter fit model (AMOUNTS), which takes into account possible interannual variation due to the quasi-biennial oscillation (QBO) and volcanic eruptions.
 
 

Reference for AMOUNTS:

 Keckhut, P. et al., Midlatitude long-term variability of the midle atmosphere: trends and cyclic and episodic changes, J. Geophys. Res., 1995, 100, 18887-18897
 
 
 
 


Stratospheric Dynamics
Preferred Presentation: oral

Interannual variations of polar ozone losses and the general circulation

Hirooka, Toshihiko; Watanabe, Shingo; Iwao, Koki

Interaction of polar ozone losses and polar vortex
Polar ozone losses versus strength of polar vortex

Polar ozone losses during winter and spring are controlled by chemical and transport processes which are largely influenced by dynamical conditions, e.g., planetary wave activity and/or stratospheric sudden warmings. Such polar ozone losses would in turn bring about changes of the dynamical field, because less ozone means less absorption of solar UV radiation and a cooler stratosphere. Consequently, the polar ozone losses interannually change, interactively connected with the dynamical field.
 
 

In order to see the property of such interannual variability and interaction mechanism between ozone and dynamical fields, we performed an ozone depletion experiment with polar ozone losses over 50 successive years by the use of a general circulation model including simplified ozone photochemistry (Watanabe et al., 2002). The resultant interannual variability of the general circulation in the stratosphere becomes larger than that in an experiment without polar ozone losses, which is intimately connected with the change of UV heating due to the polar stratospheric ozone change. The interannual variation shows an annular seesaw pattern between the Arctic and mid-latitudes in the stratosphere, which furthermore extends down to the troposphere and forms the "Arctic Oscillation."
 
 

Moreover, although external parameters such as surface boundary conditions are fixed, a decadal variation consisting of strong and weak wave activity periods appears in the ozone depletion experiment. In the strong wave activity period, sudden warmings frequently occur and polar ozone losses are correspondingly small. Such a character is consistent with observations: in recent years, frequent occurrence of major warmings is observed after a relatively quiet decade of 1990s. The existence of the decadal variation implies the importance of the interaction of ozone and dynamical fields, which also makes it difficult to estimate precisely future trends of ozone and the general circulation.
 
 

REFERENCE
 
 

Watanabe, S., T. Hirooka and S. Miyahara, 2002: Interannual variations of the general circulation and polar stratospheric ozone losses in a general circulation model. J. Meteorol. Soc. Japan, 80(4B), 877-895.
 
 
 
 


Stratospheric Dynamics
Preferred Presentation: poster

Variation in instantaneous lifetimes of ozone depleting substances, in relation to stratospheric circulation

Hoyle, Christopher; Rozanov E.; Egorova, T.; Peter T.

general circulation
Lifetimes of Ozone Depleting Substances

In order to predict the rate at which the reduction of Ozone Depleting Substances (ODS) in the stratosphere (and consequently the recovery of

 the ozone layer) will proceed, it is vital to anticipate how the lifetimes of ODS will develop in the future. To provide an insight into the link between ODS lifetime and general circulation, the 3-D offline chemical transport model MEZON is used. The results of multi-year simulations using input fields from both ERA-40 and UKMO assimilations are presented, in which a correlation between variation in the instantaneous lifetimes of ODS and changes in aspects of the stratospheric circulation over the last 10 years is sought.
 
 


Stratospheric Dynamics
Preferred Presentation: oral

Relation between stratospheric ozone and climate deduced from total ozone data

Hudson, Robert; Andrade, Marcos Follette, Melanie

Movement of the upper troposphere meteorological fronts
Mean position of the meteoroloical fronts

In a recent paper, Hudson et. al. (2003), presented evidence that the Northern hemisphere total ozone field can be separated into distinct regimes, the boundaries of which are the subtropical and polar upper troposphere fronts, and, in the winter, the polar vortex. It was also shown, that the tropical, midlatitude, and polar regimes were identified with a distinct tropopause height. In addition, in any month, a unique total ozone value and a distinct ozone profile shape could be assigned to each of the three regimes. Previous studies of the variability of total ozone and profiles have centered on zonal averages over specific latitude bands. However, the boundaries of the regimes are the upper troposphere meteorological fronts, which follow the Rossby waves at the tropopause. These waves meander over a wide range of latitudes, and, because the mean total ozone and the ozone profile are almost constant within a regime, a zonal average will depend on the relative area of the respective regimes. Analysis of the ozone field in the Northern Hemisphere outside of the polar vortex, using both TOMS and Dobson data, has shown that the trends in total ozone between 1979 and 1992 within each regime are smaller than the overall mid-latitude trend obtained from zonally averaged data. Much of the observed zonal trend is due to the movement of the subtropical and polar front northward, causing more low ozone in the tropical regime, and less high ozone in the polar regime, to be included in the zonal average. This movement of the fronts implies that the weather patterns associated with these fronts will also have moved northward, i.e. that a change in climate has taken place. This paper presents an analysis of the movement of the polar and sub-tropical fronts for the period between 1965 and 2002 deduced from both the TOMS and Dobson data sets.

REFERENCE: R. D. Hudson, A. D. Frolov, M. F. Andrade, and M. B. Follette,' The Total Ozone Field Separated into Meteorological Regimes, Part I:, Defining the Regimes', JAS, 60, 1669-1677, 2003.
 
 
 
 


Stratospheric Dynamics
Preferred Presentation: poster

Specified Ozone Production and Loss

Jackman, Charles; Kawa, Randy Douglass, Anne

Total Ozone Prediction
Predict Ozone from Specified Ozone Production & Loss

The correct prediction of total ozone as a function of latitude and season is extremely important for global models. This exercise tests the ability of a particular model to simulate ozone. The ozone production (P) and loss (L) will be specified from a well- established global model and will be used in all GCMs for subsequent prediction of ozone. This is the "B-3 Constrained Run" from M&MII. The exercise mostly tests a model stratospheric dynamics in the prediction of total ozone. The GCM predictions will be compared and contrasted with TOMS measurements.

 REFERENCE: Models and Measurements II, J. H. Park et al., NASA/TM-1999-209554, see p. 20, pp. 384-396, 1999.
 
 


Stratospheric Dynamics
Preferred Presentation: poster

Observational constraints on modeling the dynamic troposphere-stratosphere coupling

Judith Perlwitz

Dynamic interaction between the troposphere and stratosphere
Process-oriented validation of mechanisms

We suggest a framework for a process-oriented validation of atmospheric circulation models in representing the mechanisms of the dynamic troposphere-stratosphere coupling. This framework is based on characteristic features of the dynamic troposphere-stratosphere coupling isolated on daily time scale. The comparison of these features between observations and coupled chemistry-climate models will help to explain the response of stratospheric and tropospheric circulation to anthropogenic forcing. The statistical approach is introduced, observational results are shown and examples based on the ECHAM4 and GISS model are presented.
 
 


Stratospheric Dynamics
Preferred Presentation: oral

Planetary waves in observations and model results with the ECHAM4/CHEM model

Mager, Fabian; Dameris, Martin

Troposphere-stratosphere Interaction by planetary waves
Analysis of transient and stationary waves

The wavenumber-frequency analysis method has been sparsely used in atmospheric sciences in the last 15 years despite its numerous aplications. The method calculates power spectra, coherence and phase of transient large-scale Rossby waves from time series of Fourier coefficients (Hayashi 1977, 1982). At DLR, this method was employed to study how accurate the ECHAM4.L39(DLR)/CHEM chemistry-climate model (Hein et al., 2001) represents these waves in comparison to ECMWF reanalyses and how they change trough different time-slice experiments.

 The model represents well the observed wave amplitudes not only in the different considered frequency bands but also in the sum over all frequencies. It simultates well the baroclinic character of travelling waves in respect to vertical amplitude growth and inclination. A remarkable feature of the model is its ability to simulate so-called "normal modes" very accurately.

 Apart from the mentioned analysis of transient waves, stationary wave patterns have been investigated. Both analyses are used to detect and explain dynamical mechanisms by which the troposphere acts upon the stratosphere.
 
 

Hayashi, Y., 1977: On the coherence between progressive and retrogressive waves and a partition of space-time power-spectra into standing parts.

J. Meteor. Soc. Japan, 16, 368-373
 
 

Hayashi, Y., 1982: Space-time spectral analysis and its applications to atmospheric waves.

J. Meteor. Soc. Japan, 60, 156-171
 
 

Hein, R., M. Dameris, C. Schnadt, C. Land, V. Grewe, I. Köhler, M Ponater, R. Sausen, B. Steil, J. Landgraf, and C. Brühl, 2001: Results of an interactively coupled atmospheric chemistry-general circulation model: Comparison with observations.

 Ann. Geophys., 19, 435-457
 
 
 
 


Stratospheric Dynamics
Preferred Presentation: oral

Sensitivity of the middle atmosphere to ozone depletion and increase in greenhouse gases with the MAECHAM4/CHEM chemistry climate model

Manzini, Elisa; Steil, Benedikt; Bruehl, Christoph; Giorgetta, Marco; Kreuger, Kristin

Wave driving
Transformed Eulerian Mean Diagnostics

The sensitivity of the middle atmosphere circulation to ozone depletion and increase in greenhouse gases is assessed by performing multiyear simulations with the MAECHM4/CHEM chemistry climate model. Results are reported for three simulations with fixed boundary conditions: one for the near-past (1960) and two for the near-present (1990 and 2000) . Changes in ozone are simulated interactively by the coupled model. We focus on the importance of diagnosing dynamical processes in order to interpret the simulated changes in temperature. In the Arctic lower stratosphere, a cooling in March with respect to the 1960 simulation is found only for the 2000 simulation. Wave activity emerging from the troposphere is found to be comparable in the winters of the 1960 and 2000 simulations, suggesting that ozone depletion and greenhouse gases increase contribute to the 2000-1960 March cooling in the Arctic lower stratosphere. The comparison of the 1960 and 2000 simulations shows an increase in downwelling in the mesosphere at the time of cooling in the lower stratosphere (March). The mesospheric increase in downwelling can be explained as the response of the gravity waves to the stronger winds associated with the cooling in the lower stratosphere. Planetary waves appear to contribute to the downward shift of the increased downwelling, with a delay of about a month. The increase in dynamical heating associated with the increased downwelling may limit the cooling and the strengthening of the lower stratospheric polar vortex from above, facilitating ozone recovery and providing a negative dynamical feedback. References: Manzini et al, J. Geophys. Res., 108, doi:10.1029/2002JD002977, 2003; Steil et al, J. Geophys. Res., 108, doi:10.1029/2002JD002971, 2003.
 
 


Stratospheric Dynamics
Preferred Presentation: oral

Signature of AO phase in the lower stratosphere ozone and temperature

Rozanov., Eugene; Egorova, Tatiana Schmutz, Werner Zubov, Vladimir

Meridional transport
Composite analysis of the model output and observational data

We intend to validate the imprint of the Arctic Oscillation in the meridional circulation intensity as well as in the stratospheric ozone and temperature distributions. The output from 40-year long run of CCM ?SOCOL? will be divided into two groups according AO phase and their difference will be analyzed against observational data processed using the same procedure. It is expected that during the years with more stable polar vortex the model simulates elevated ozone mixing ratio and higher temperature in the tropical lower stratosphere as a result of weaker meridional circulation.
 
 


Stratospheric Dynamics
Preferred Presentation: oral

Short term ozone variability - Ozone miniholes

Stenke, Andrea; Grewe, Volker

Ozone Minihole formation
SPECIFIC Frequency distribution of Ozone miniholes

The winter and spring stratospheric extra-tropical ozone layer shows a high variability on a day by day scale. A large part of this variability is produced by so-called ozone miniholes, which in this sense are produced by upper troposphere ridges, leading

 to divergence in the stratosphere. The changes are of the order of 10% per day. The analysis technique for detecting and tracking mini-holes, developed by James (1998), is based on daily fields of total ozone and can be applied in the same way to observational data and model data. An example is given by Stenke and Grewe (2003).

 Additionally ozone mini-holes have the potential to activate chlorine at the vortex edge and are therefore important for ozone chemistry.
 
 

REFERENCE:

James, PM, 1998, A climatology of ozone mini-holes over the northern hemisphere, Int. J. Climatol. 18, 1287-1303.

 Stenke, A., and Grewe V., 2003, Impact of ozone mini-holes on the heterogeneous destruction of stratospheric ozone, Chemosphere, 50, 177-190.
 
 
 
 


Stratospheric Dynamics
Preferred Presentation: poster

Tropical isolation in the middle stratosphere as shown by CLAES N2O measurements

Strahan, Susan; Douglass, Anne

Tropical isolation in the middle stratosphere
Shape of the tropical and midlatitude N2O probability distribution function

The bimodality of probability distribution functions (pdfs) of CLAES N2O between 10oS and 45oN is used to assess a model's ability to produce sufficient tropical/midlatitude isolation. The apparent barrier arises from midlatitude wave activity that cannot penetrate the tropics, resulting in distinctly different tracer mixing ratios in the two regions. Ascent of young air gives high N2O values in the tropics, while descent of older air in the middle and high latitudes results in lower mixing ratios and a broad distribution. Isolation is evaluated on 4 theta surfaces from 600-1200K. A broad latitude range is chosen so that QBO phase-dependent variations in the subtropical boundary will not affect the modality of the pdf. The phase-dependent secondary circulation set up by the QBO causes significant interannual variability in constituent mixing. Because CLAES N2O data do not cover a full QBO cycle, we compare only the modality of the distribution and not the mixing ratios or the separation of the peaks.

The CLAES N2O pdfs show a two-peak distribution in summer, fall, and winter, with a varying depth of the minimum, indicating tropical isolation. (Spring is excluded because a previous study found the distribution to be nonstationary.) Models are judged by whether they produce a bimodal pdf similar to the CLAES results. A model that produces a single peak indicates a lack of tropical isolation, which may have significant chemical consequences. Excessive transport out of the tropics near the NOy maximum (~1200K) can increase summer high latitude NOx, directly increasing O3 loss and indirectly affecting O3 by perturbing ClOx levels.
 
 
 
 


Transport Characteristics
Preferred Presentation: oral

Model grid zooming and the impact on tracer distributions in the Arctic lower stratosphere

Bregman, Bram; Van den Broek, M.;Van Aalst, M.;Krol, M.;Lelieveld, J.;Toon, G.C.;Garcelon, S.;Hansford, G.M.;Jones, R.J.;Gardiner, T.D;Berthet, G.

stratospheric model transport of methane
model grid zooming

This study reports on CH4 distributions in the 1999-2000 winter Arctic lower stratosphere, utilizing a model grid zooming algorithm in a 3D Chemistry-transport Model (CTM). Three different zooming options up to 1x1 degree horizontally have been explored, including different vertical resolutions up to the 60 layers of the ECWMF assimilation data, which is the driving meteorology of the model. The results have been compared with balloon-borne observations. In addition, a model intercomparison was performed with the 3D CTM REPROBUS. Differences are discussed in the context of model grid resolution and advection.
 
 


Transport Characteristics
Preferred Presentation: poster

Ozone Seasonal Cycles

Douglass, Anne; Kawa, Randy Jackman, Charles

Transport, photochemical production and loss
Ozone seasonal cycles as functions of latitude and altitude

Observations from various satellite instruments (e.g., Total Ozone Mapping Spectrometer (TOMS), Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS)) specify the latitude and seasonal variations of total ozone and ozone as a function of altitude.  These seasonal variations change with latitude and altitude partly due to seasonal variation in transport and temperature, partly due to differences in the balance between photochemical production and loss processes, and partly due to differences in the relative importance of the various ozone loss processes.  Comparisons of modeled seasonal ozone behavior with observations test the following:

 ? the seasonal dependence of dynamical processes where these dominate the ozone tendency;

 ? the seasonal dependence of photochemical processes in the upper stratosphere;

 ? the seasonal change in the balance between photochemical and dynamical processes.
 
 
 
 
 
 



Transport Characteristics
Preferred Presentation:

N2O and NOy

Kawa, Randy; Jackman, Charles Douglass, Anne Strahan, Susan

Large Scale Tracer Transport; N2O and NOy Loss Chemistry
N2O, NOy mixing ratios, gradients, and correlations

N2O and NOy
 
 

The principal loss processes for ozone in the stratosphere are either directly or indirectly closely coupled to the abundance and distribution of reactive oxides of nitrogen (NOy). The main source of NOy in the stratosphere is N2O, a trace gas that is changing significantly as a result of anthropogenic forcing. Thus diagnosis of the distributions of N2O, NOy, and their coupling is required to evaluate any chemistry-climate model aspiring to accurately simulate ozone change. In the NASA Assessment of the Effects of High-Speed Aircraft in the Stratosphere:1998 we found that the sensitivity of various models? ozone to perturbation did correspond consistently with their background NOy distribution. Coordinated NOy and N2O mixing ratio distributions are available from observations: ER-2 aircraft in the lower stratosphere and ATMOS and balloon profiles to higher altitudes at a subset of latitudes and seasons. Although close comparison to these diagnostics is crucial, unfortunately the distributions are due to a combination of transport and chemical processes, and isolating the source of differences is not always simple. However, in combination with other transport and photochemical diagnostics, comparison with N2O and NOy can be very instructive in evaluation of model processes and performance.
 
 
 
 
 
 


Transport Characteristics
Preferred Presentation: poster

Quantification of horizontal transport processes in the Berlin Climate Middle Atmosphere Model with interactive chemistry

Krüger, Kirstin; Grenfell, John Lee; Mieth, Peter; Langematz Ulrike, and Steil Benedikt

Polar and mid-latitude ozone loss
Criterion to identify streamers, climatology of stratospheric streamers

We present a newly-developed version of the Free University of Berlin Climate Middle Atmosphere Model with interactive chemistry (FUB CMAM CHEM) and a semi-Lagrangian transport scheme to advect chemical species. For the past and present climate runs described here we used climatological SSTs and adopted the IPCC-IS92a scenario for the CFCs and well-mixed GHG changes performed with fixed boundary conditions for the years 1980 and 2000. The dynamics of the middle atmosphere will be validated using recently-available observational data sets. Particular interest will be placed on the model's ability to reproduce horizontal transport processes e.g. the quantification of transport via stratospheric streamers through the transport barriers.
 
 


Transport Characteristics
Preferred Presentation: poster

Age-of-air simulation using the New-Dynamics Unified Model

Morgenstern, Olaf; Zeng, Guang Braesicke, Peter Pyle, John Johnson, Colin

Age of air
Age of air tracer

The Unified Model is the operational weather prediction and climate model used by the U.K. MetOffice. It has recently undergone a substantial revision; most importantly, it is now the first climate model using non-hydrostatic dynamics on a geometric-altitude grid. In an effort to assess tropospheric and stratospheric transport characteristics of that model, we perform a radon-lead experiment in which radon is emitted at a uniform rate from land points and decays exponentially to form lead. Unlike in the real atmosphere, model lead is an inert tracer and accumulates during the course of the experiment; it is hence suitable as an age-of-air tracer. We assess transport characteristics of the model as inferred from this experiment.
 
 


Transport Characteristics
Preferred Presentation: oral

Vortex edge development and erosion demonstrated by HALOE CH4 measurements

Strahan, Susan; Douglass, Anne

Vortex edge development and erosion
Evolution of CH4 probability distribution functions in the polar region in spring

The evolution of HALOE CH4 distributions in Austral spring reveals the process of vortex breakdown in the Antarctic lower stratosphere. This test examines the evolution of probability distribution functions (pdfs) of two latitude bands, 60-80oS and 44-60oS, on the 450K and 600K surfaces. The former band is almost strictly vortex air in early spring, retaining a small, isolated vortex core into November. The latter band is almost strictly midlatitude, or `surf zone', air. The dynamics of vortex breakdown and the extent and direction of mixing between the vortex and surf zone are revealed by several features of the pdfs: the separation of the peaks, the depth of the minimum between the peaks, and changes in the most probable values. Low interannual variability in the southern hemisphere allows 8 years of HALOE CH4 data to be combined to provide the basis for this test. HALOE provides sufficient high latitude coverage in March and April to provide a test for the Arctic vortex as well.

 HALOE September data at 450K show broad but distinct distributions with peaks separated by a shallow minimum. This indicates that the vortex edge is not yet a strong barrier to mixing. In October and November, the appearance of a deep minimum indicates the development of a very sharp boundary between the vortex and surf zone. In November, the vortex pdf maintains a low mean value with a long, low mixing ratio tail. The development and maintenance of this bimodal structure with a deep minimum show that the vortex breaks down by erosion. Air leaving the vortex is rapidly mixed into the surf zone but the vortex itself shows no evidence of influence from the surf zone. The HALOE data at 600K give a similar picture of breakdown by erosion with an even stronger barrier to exchange. There are significant chemical consequences for models that show mixing between the vortex and surf zone. For example, PSC processing and O3 loss may come to a premature end due to unphysical mixing which resupplies NOx and HCl to the denitrified vortex.
 
 
 
 


Transport Characteristics
Preferred Presentation: oral

Tracer Mixing in the Extratropical Tropopause Region

Wirth, Volkmar; Lopez Juan-Fran

Mixing
Contour length and its change through coarse graining

Both airborne measurements and satellite images indicate that tracers in the extratropical tropopause region have complex structures at scales well below the resolution of most numerical models. The topology of such tracer structures affects the mixing between stratospheric and tropospheric species and is, therefore, likely to have an impact on chemistry. The current work tries to understand basic features of tracer structures in the tropopause region due to balanced motion in the neighborhood of tropopause anomalies. More specifically, layerwise twodimensional tracer advection is investigated in the frame-work of Juckes's idealized quasi-geostrophic tropopause model. At initial time the tracer is specified to be column-like in the vertical with its horizontal structure corresponding to that of the tropopause anomaly. Although highly idealized, this setup is argued to be relevant for the mixing between stratospheric and tropospheric air in the real atmosphere. The equations are numerically integrated over synoptic time scales with very high spatial resolution using a contour dynamical implementation. The analysis focuses on the complexity of the interface between stratospheric and tropospheric air using contour length and its change through coarse graining as diagnostic tools. It is found that the rate of filamentation and the mixing efficiency systematically depend on altitude with maximum values at an intermediate distance from the tropopause. This behavior results from a competition between the decrease of the average rate of strain with increasing distance from the tropopause and the transition from "dynamically active" to "dynamically passive" tracer behavior. Implications for chemical reactions with their rate limited by the mixing efficiency will be discussed.
 
 
 
 


Tropospheric Forcing
Preferred Presentation: poster

The interactive chemistry climate model MAECHAM4-CHEM, longterm simulations for near past, present and near future (part 2)

Bruehl, Christoph; Steil, Benedikt; Manzini, Elisa

Sea Surface Temperature effects on stratospheric circulation and polar chemistry
dynamical heating and cooling

Results of eight 20-year time-slice experiments with the chemistry-climate model MA-ECHAM4-CHEM for typical boundary conditions from 1960 to 2030 are presented. To separate effects, for 1990 3 different sea-surface temperature data sets were selected, for 2000 2 different stratospheric chlorine concentrations, and for 2030 a scenario which considers the stratospheric cooling by enhanced CO_2 only, and a scenario where all boundary conditions are changed.

 Climate interactions via gravity wave breaking in the mesosphere tend to warm the lower stratosphere in March compared to the unperturbed scenario for 1960. In the scenarios where the tropospheric temperature change is suppressed by fixing the SSTs to unperturbed values the warming in March in the lower stratosphere is almost absent due to a weakened circulation, leading to more ozone depletion than in consistent scenarios.

 (part 2 of Poster 25, references there; see also poster by Manzini et al on stratospheric dynamics)
 
 


Tropospheric Forcing
Preferred Presentation: poster

The interactive chemistry climate model MAECHAM4-CHEM, longterm simulations for near past, present and near future (part 2)

Bruehl, Christoph; Steil, Benedikt; Manzini, Elisa

Sea Surface Temperature effects on stratospheric circulation and polar chemistry
dynamical heating and cooling

Results of eight 20-year time-slice experiments with the chemistry-climate model MA-ECHAM4-CHEM for typical boundary conditions from 1960 to 2030 are presented. To separate effects, for 1990 3 different sea-surface temperature data sets were selected, for 2000 2 different stratospheric chlorine concentrations, and for 2030 a scenario which considers the stratospheric cooling by enhanced CO_2 only, and a scenario where all boundary conditions are changed.

 Climate interactions via gravity wave breaking in the mesosphere tend to warm the lower stratosphere in March compared to the unperturbed scenario for 1960. In the scenarios where the tropospheric temperature change is suppressed by fixing the SSTs to unperturbed values the warming in March in the lower stratosphere is almost absent due to a weakened circulation, leading to more ozone depletion than in consistent scenarios.

 (part 2 of Poster 25, references there; see also poster by Manzini et al on stratospheric dynamics)
 
 


Tropospheric Forcing
Preferred Presentation: oral

Fingerprinting the ozone signatures of climate patterns

Orsolini, Yvan; Doblas-Reyes, Francisco

process
diagnostic

Column ozone observations from both ground-based and satellite instruments reveal a springtime decrease over the northern hemisphere high and middle latitudes in recent decades. However, there is a considerable inter-annual and decade-to-decade variability superimposed on the weak trend. One challenge is to understand the nature and the physical processes behind the dynamical contribution to the trend and variability.

We show how to estimate the influence of low-frequency tropospheric dynamics upon column ozone inter-annual variability, with a focus on the spring season and the Euro-Atlantic sector. This dynamical variability of tropospheric origin is examined in terms of leading climate patterns, derived from an empirical orthogonal function analysis of 500mb geopotential heights. In order to fingerprint the spatial and temporal ozone signatures of these patterns, the Total Ozone Mapping Spectrometer (TOMS) satellite observations of column ozone during the last two decades are used. We extract by linear regression the geographical ozone signatures of these climate patterns, and reconstruct their time evolution.
 
 

A whole series of leading patterns of variability, for examples the North Atlantic Oscillation, the Scandinavian pattern, the East-Atlantic pattern and European blocking patterns, induce column zone anomalies in the range of 5-15 Dobson Units per standard deviation of the pattern index. The impact of these combined Euro-Atlantic climate patterns upon the regional ozone trends and inter-annual variability is also estimated. Their coupling with the stratosphere is also examined, and a hitherto little-known lifting of the Arctic tropopause by the polar night jet is also shown to imprint upon the ozone signatures of some patterns. In addition, we discuss the remote coupling of the patterns with the Pacific sector.
 
 

We discuss how to diagnose long chemistry/climate model simulations for such signatures, a research activity which is planned in a Norwegian climate project (AEROZKLIM, Dr. Isaksen, Coord.).
 
 
 
 


Tropospheric Forcing
Preferred Presentation: oral

North Atlantic Oscillation changes and stratospheric ozone recovery in the Northern Hemisphere in a chemistry-climate model

Schnadt, Christina; Dameris, Martin

tropospheric wave acitivity, stratospheric ozone loss
NAO index composites of dynamical fields

The relationship between North Atlantic Oscillation (NAO) changes and

northern stratospheric ozone recovery in the near future is

investigated using four timeslice scenarios (1960, 1980, 1990, 2015) of the chemistry-climate model ECHAM4.L39(DLR)/CHEM. A wintertime NAO index composite study of the scenario "1990" and of the ECMWF reanalyses shows the typical NAO patterns: in the positive phase

the stratospheric polar vortex is stronger and colder than in the negative phase. In the troposphere, the positive phase is marked by increased variance across the North Atlantic stormtrack whereas the negative phase is suggestive of blocking. Consistently, vertical stationary (transient) wave propagation is reduced (enhanced) in the positive phase. The model NAO index decreases significantly from "1990" to "2015". This coincides with enhanced vertical stationary wave propagation and a dynamical warming of the northern polar stratosphere. Thus, tropospheric circulation changes might influence stratospheric dynamics and hence northern hemisphere ozone evolution.
 
 


Tropospheric Forcing
Preferred Presentation: oral

Simulation of the separate climate effects of stratospheric and tropsopheric CO2 doubling

Siegmund, Peter; Sigmond, Micheal Kelder, Hennie

anthropogenic greenhouse gas increase and dynamic changes in the troposphere and stratosphere
CO2 doubling and coupling stratospheric and tropospheric dynamic changes

The separate effects of stratospheric and tropospheric CO2 doubling have been simulated and analysed with the ECHAM middle atmosphere climate model. The CO2 concentration has been uniformly doubled in the atmosphere, and separately in the stratosphere and troposphere. During the NH winter, the uniformly doubled CO2 climate shows an increase of the stratospheric residual circulation, a small warming in the Arctic lower stratosphere, a weakening of the zonal winds in the Arctic middle stratosphere, an increase of the tropospheric NH mid-latitude wetserlies, and a poleward shift of the tropospheric SH westerlies. The uniformly doubled CO2 response is in most regions approximately equal to the sum of the separate responses to tropospheric and stratospheric CO2 doubling. The tropospheric CO2 doubling contributed about two third to the strengthening of the stratospheric residual circulation. This increase contributes to the Arctic lower stratospheric warming and to the weakening of the Arctic middle stratospheric zonal wind. Stratospheric CO2 doubling is the major contributor to the increase of tropospheric NH mid-latitude wetserlies, indicating its crucial importance for tropospheric climate change. A significant influence on tropospheric climate is also found for CO2 doubling above 10 hPa, which is above the top of many GCMs.
 
 


Tropospheric Forcing
Preferred Presentation: oral

Dynamical control of ozone transport and ozone chemistry from satellite observations and coupled chemistry-climate models

Weber, Mark; Eyring, Veronika; Dhomse, Sandip; Wittrock, Folkard; Dameris, Martin

Transport of ozone into mid-to high latitude
Total ozone and chlorine dioxide column and the relationship to eddy heat flux

Planetary scale wave driving regulates the winter transport of ozone into mid-to high latitude as part of the residual circulation. In addition the strength of the residual circulation regulates stratospheric temperatures at high latitudes and thus controls chemical depletion and in particular its interannual variabilty during Arctic winters. Using total ozone and chlorine dioxide column measurements from GOME the close interaction between ozone transport and ozone chemistry and the relationship to eddy heat flux variability will be investigated combining data from both hemispheres and using different meteorological analyses (NCEP, UKMO, ERA15 and ERA40). The GOME data period (1995-2003) represents a time close to the maximum of stratospheric halogen loading. By using TOMS total ozone data differences in the compact relationship between winter ozone transport in the past (early 80s) and present have been investigated and are compared with analogous relationships derived from different time slice ECHAM4.L39(DLR)/CHEM model runs. Apart from uncertainties in the diagnostic capabilities of CCMs, the differences in dynamical proxies derived from different meteorological analysis have a large impact on the diagnostic relationships derived.
 
 


Tropospheric Forcing
Preferred Presentation: oral

Column ozone and the residual circulation

Wohltmann, Ingo; Rex, Markus; Eyring, Veronika; Dameris, Martin

Transport of ozone by the residual circulation
EP flux (100 hPa, 45-75 deg N) vs. total ozone column

The transport of ozone by the residual circulation has just recently been put into perspective as an important contributor to the year-to-year variability in the ozone column at all latitudes [1,2]. The residual circulation is driven by tropospheric waves propagating into the stratosphere, which can be seen by the TEM formulation of the equations governing atmospheric dynamics [3]. The tropospheric wave forcing can be well characterized by the integrated Eliassen-Palm flux entering the stratosphere, which controls the winter/spring build-up in stratospheric ozone.

Fluxes calculated from reanalysis data (NCEP or ECMWF) can be correlated with ozone columns from long term data sets like Arosa or the TOMS/SBUV merged satellite data set. Explained variances in total ozone can reach up to 50% in high latitude spring, but typically lie between 15% and 25%. This couples the column amounts in the stratosphere directly to changes in tropospheric circulation.

 Care has to be taken in the statistical analysis of the correlations and in regard to the long term stability of the used data sets.

 References: [1] Fusco and Salby, J. Clim., 12, 1619, 1999 [2] Randel et al., J. Meteor. Soc. Jap., 80, 4b, 849, 2002 [3] Andrews et al., Middle Atmosphere Dynamics, Academic Press, 1987