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.
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.
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.
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.
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.
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.
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!
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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)
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.
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
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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)
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)
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.).
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.
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.
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.
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