Abstracts
66 abstracts
divided into 9 Categories:
A. Dynamics (9 abstracts)
B. Stratospheric Transport (5 abstracts)
C. Upper Troposphere / Lower
Stratosphere (14 abstracts)
D. Radiation (3 abstracts)
E. Stratospheric Chemistry and
Microphysics (10 abstracts)
F. Natural Variability (5 abstracts)
G Long Term Changes in the
Stratosphere (15 abstracts)
H Effect of Stratosphere on
Troposphere (4 abstracts)
I Database (1
abstract)
A. Dynamics
Abstract A1 (Poster)
Hemispheric ozone variability indices derived from satellite
observations and comparison to CCMs
Thilo Erbertseder, Veronika
Eyring, Michael Bittner, Martin Dameris,
and CCMVal team
Total
column ozone is used to trace the dynamics of the lower and middle stratosphere
which is governed by planetary waves. In order to analyse
the planetary wave activity a Harmonic Analysis is applied to global multi-year
total ozone observations from the Total Ozone Monitoring Spectrometer (TOMS).
As
diagnostic variables we introduce the hemispheric ozone variability indices one
and two. They are defined as the hemispheric means of the amplitudes of the
zonal waves number one and two, respectively, as traced by the total ozone
field.
The
application of these indices as a simple diagnostic for the evaluation of
coupled chemistry-climate models (CCMs) is
demonstrated by comparing results of the CCM ECHAM4.L39DLR/CHEM (hereafter:
E39/C) against satellite observations. It is quantified to what extent a
multiyear model simulation of E39/C representing 2000 climate conditions is
able to reproduce the zonal and hemispheric planetary wave activity derived
from TOMS data.
We are
planning to apply this analysis to multi-year total ozone data from transient
CCM simulations. It will be quantified to what extent the CCMs
are able to reproduce the zonal and hemispheric planetary wave activity.
Abstract A2 (Oral)
Evaluation of the response of the stratosphere to ENSO events in CCMs
Chiara Cagnazzo, E. Manzini,
H. Akiyoshi, J. Austin, S. Bekki,
C. Bruhl, N. Butchart, M. Chipperfield, M. Dameris, M. Deushi, A. Douglass,
V. Eyring, F. Jegou, R.
Garcia, A. Gettelman, M.A. Giorgetta,
V. Grewe, D. Hauglustaine,
D. Kinnison, E. Mancini, D. Marsh, T. Nagashima, P. Newman,
S. Pawson, G. Pitari,
D. Plummer, E. Rozanov, M. Schraner,
J. Scinocca, K. Shibata, R. Stolarski,
H. Struthers, M. Takahashi and W. Tian
The
effect of ENSO events on the northern winter polar stratospheric circulation is
addressed through the analysis of simulations with observed SSTs recently
performed with 13 Chemistry Climate Models. Composites of temperature, zonal
winds, geopotential height and total ozone fields
from time series of an ENSO index for cold, neutral and warm SST conditions
have been constructed.
Given
that the internal variability is high and the external forcing included in the
simulations, results from investigations indicate that the stratospheric polar
warming possibly associated with ENSO is quite different across the models in
terms of altitude, month and amplitude of occurrence. In order to identify the
coherence in the responses across the models and to understand the causes of
the range of stratospheric responses in terms of simulation designs and model
biases, the response of the model to ENSO in the tropical and extratropical troposphere is also analysed.
Abstract A3 (Poster)
Modelling the effects of a
realistic QBO on Antarctic ozone variability
Steve George and Adrian McDonald
The size
and intensity of the Antarctic ozone hole is known to be influenced by a number
of natural and anthropogenic factors. This is due to the heterogeneous
chemistry of ozone destruction being extremely sensitive to changes in
stratospheric temperature within the polar vortex. Defining temperature anomaly
mechanisms is crucial if one wishes to understand the austral springtime
formation, and interannual variability, of the ozone
hole.
Recent
work using a chemistry-climate model (SOCOL) has investigated chemical and
dynamical variations associated with both the solar cycle and the solar
rotation period. It is hypothesised that the model
simulation of Antarctic ozone would be significantly improved by the inclusion
of an important mode of atmospheric variability known as the Quasi-Biennial
Oscillation (QBO).
The QBO
dominates the variability of the equatorial stratosphere and is characterised by downward propagating easterly and westerly
wind regimes, with a variable period averaging 28 months. Although essentially
equatorial in nature, several studies have shown evidence of a relationship
between QBO phase and Antarctic ozone loss. The mechanism is as yet not
completely understood, but a likely candidate is that induced
changes in zonal winds and potential vorticity
increases the effectiveness of wave energy propagation to high latitudes
in the easterly phase while reducing it in the westerly phase. In turn,
temperatures in the Southern Hemisphere stratosphere are respectively increased/reduced with associated impacts on the nonlinear
heterogeneous ozone chemistry.
Present-generation
model resolution limits the explicit representation of small-scale wave sources
that help drive the QBO e.g. deep convection, boundary-layer turbulence.
Instead, this non-orographic gravity wave drag (NOGWD)
can be parameterised by defining an energy launch
spectrum in the troposphere or lower stratosphere. This presentation discusses
a new SOCOL NOGWD scheme of a type initially described by Warner and McIntyre
which has since been used successfully in the Canadian Middle Atmosphere Model.
Comparison will be made with the original, non-QBO resolving, SOCOL model.
Abstract A4 (Poster)
Stratospheric Climate and Circulation Changes
Neal Butchart, Veronika Eyring, Darryn Waugh, Eugene Cordero and CCMVal
Team
The CCM
simulations are used to study stratospheric climate and circulation changes. In
contrast to previous comparisons of stratospheric climate predictions, the CCM
simulations used here are all transient simulations and have almost identical
experimental set-up and forcings. The analyses
updates or extends the few other published intercomparisons
of stratospheric predictions, including the heat flux - temperature
relationship as assessed in Austin et al. (2003), temperature changes discussed
in Eyring et al. (2006) and the changes in tropical
upwelling considered by Butchart et al. (2006). We
present those aspects of stratospheric climate and circulation change which are
robust, i.e. model independent. A more detailed analysis of temperature changes
than in Eyring et al. (2006) considers the seasonal
and spatial distribution of the trends and separate secular trends from low
frequency variability. The relative importance of the diabatic
and adiabatic contributions to the temperature changes is assessed. A key
question that is addressed is how the Arctic polar vortex changes in the
REF2/SCN2 simulations. Other key questions are: what are the predicted changes
in the Brewer-Dobson circulation and to what extent are these changes related
to age of air changes in the different models. Also how do changes in tropical
upwelling relate to changes in polar downwelling.
Abstract A5 (Oral)
Ozone Radiative Feedback on the Quasi-Biennial
Oscillation
Kiyotaka Shibata and Makoto Deushi
Simulations
of the recent past stratosphere and mesosphere were made with a
chemistry-climate model (CCM) of Meteorological Research Institute (MRI). Three
runs with different transport schemes for chemical species were performed for
25 years from 1980 to 2004. The three transport schemes are formally hybrid
semi-Lagrangian type, which is of flux form in the
vertical and, at once, of ordinary type in the horizontal, while they use
different interpolation and/or approximation in calculating in-cell profiles
from cell-average values, resulting in different properties in diffusiveness.
The prototype scheme Cubic3 uses a Lagrangian cubic
interpolation of neighbouring abundances in the
horizontal and also uses it for overhead column abundances in the vertical. To
the Cubic3 scheme, two improvements are successively incorporated: one is the
piecewise rational-function method (PRM) in the vertical, and the other is a quintic Lagrangian interpolation
in the horizontal, resulting in PRM3 vertically PRM and horizontally cubic and
PRM5 vertically PRM and horizontally quintic schemes.
The
dynamics module of MRI-CCM is a spectral global model of T42 truncation with 68
layers extending from the surface to 0.01 hPa (about
80 km), wherein the vertical spacing is 500m in the stratosphere between 100 hPa and 10 hPa. Hines gravity
wave (GW) drag is incorporated with an enhanced GW source in the tropics to
spontaneously reproduce the QBO in zonal wind. The chemistry-transport module
treats 36 long-lived species including 7 families, and 15 short-lived species
with 80 gas phase reactions, 35 photochemical reactions and 9 heterogeneous
reactions.
MRI-CCM
is integrated with observed forcings of SSTs, sea
ice, volcanic aerosols, 11-year solar cycle, greenhouse gases, and halogens,
the latter two of which are specified at the surface. It is found that PRM3 and
PRM5 schemes substantially reduce the systematic positive bias in ozone,
particularly in the tropical lower stratosphere and upper troposphere and that
PRM5 reproduces most realistic ozone and other chemical species distributions
with PRM3 being the next. For example, the ozone decrease amounts to about 40 at 100hPa in PRM5
run. Along with these ozone reductions, the QBO period is also changed: it is
about 27 months in Cubic3 run, while it is about 23 and 20 months for PRM3 and
PRM5 runs. This shortening of the QBO period with the decrease in ozone
abundance is compatible with authors previous simulations, in which switching
on/off of ozone radiative feedback prolongs/shortens
the QBO period by about 80 35 . In a less ozone background condition in the
lower stratosphere the ozone QBO amplitude also becomes smaller, so that the
ozone radiative feedback weakens, leading to a
shorter QBO period.
Abstract A6 (Poster)
Validation of the global extratropical UTLS
region in CCMs using ACE satellite data
Michaela I. Hegglin, G. Manney, T.G. Shepherd, K.A. Walker, P. Bernath, C. Boone, P. Hoor, and
C. Schiller
The
upper troposphere/lower stratosphere (UTLS) plays a key role in
chemistry-climate coupling due to the strong radiative
impact of trace gases such as O3 and H2O in this region.
Within the ongoing CCMVal activities, a particular
effort is hence directed towards the validation of the chemical and dynamical
processes determining tracer distributions in the UTLS in CCMs.
While many diagnostics have already been proposed, most existing knowledge of
the spatio-temporal structure of chemical composition
in the UTLS, and its relation to dynamical features such as the tropopause, stems from aircraft and balloon platforms. On
the other hand, these measurements are necessarily restricted in space and
time. Satellite measurements from the Canadian Atmospheric Chemistry Experiment
(ACE) offer unprecedented accuracy and vertical resolution, allowing a new
global perspective on trace gas distributions in the UTLS and hence providing a
potentially useful data set for the CCMVal community.
We examine tracer-tracer correlations and vertical profiles of O3,
CO, and H2O relative to the local tropopause
height and show by comparison with previous aircraft measurements in the
Northern Hemisphere the high potential of the ACE measurements in resolving the
vertical structure of UTLS tracer distributions. We then compare the results to
the Canadian Middle Atmosphere Model (CMAM) and have a first glance at the
tracer evolution in a changing climate.
Abstract A7 (Poster)
Changes to Sudden Stratospheric Warmings in
Future Climates
Andrew Charlton, Lorenzo Polvani,
John Austin and Feng Li
The
dynamical coupling between the Stratosphere and Troposphere are strongest
during extreme events in the Stratosphere known as Stratospheric Sudden Warmings (SSWs). Our recent work
has focussed on establishing a new climatology of
these events and developing, dynamically realistic benchmarks for their simulation
in GCMs. Here we use these new tools together with a
state-of-the-art coupled chemistry climate model to investigate if either the
frequency or character of SSWs is predicted to change
over the coming century. Our motivation is simple, to understand what role the
stratosphere might play in future tropospheric
climate we must first understand and quantify the future stratospheric climate.
We investigate two sets of three ensemble member integrations, the first forced
with observed SSTs and climate forcings between 1960
and 2000 and the second forced with SSTs from a coupled model run forced with
trace gas concentrations based on the SRES A1B scenario of the IPCC and
equivalent climate forcings. As far as we are aware
this is the longest set of integrations used for a study of this kind. We find
an upward trend in SSW frequency of 1 SSW per decade which is statistically
significant at the 90% confidence level and is consistent over the two sets of
model integrations. Comparison of SSW climatology between the late 20th and
21st centuries in our model shows that the increase is largest toward the end
of the winter season. Comparison of the dynamical properties of SSWs in the 20th and 21st centuries shows that the
character of SSWs is not altered by the increase in
SSW frequency. This result has important consequences for prediction of the
impact of future stratospheric climate on the troposphere and also on future
concentrations of Ozone in the Northern Hemisphere stratosphere.
Abstract A8 (Withdrawn)
TropChem and CCMval
Jean-Francois Lamarque and Mark
Lawrence
I will
discuss the role of TropChem, a new IGAC/SPARC
activity that focuses on tropospheric chemistry, and
its interaction with existing programs such as CCMVal
and AEROCOM. In particular, I will
describe what TropChem can bring to the CCMVal community in terms of defining model simulations,
creating new analysis tools and organizing new science questions.
Abstract A9 (Oral)
The SPARC Dynamics and Variability Project and Connections to CCMVal
Paul Kushner et al
Several lines of evidence suggest
that the stratospheric state exerts a significant influence on the tropospheric circulation. As global climate models, which
typically represent the stratosphere poorly, become increasingly comprehensive,
important questions arise: How does a poor representation of the stratosphere
degrade the simulation of tropospheric circulation in
climate models? Furthermore, how does stratospheric representation affect the
simulated circulation
response to climate change? To address these questions the WCRP
SPARC group recently initiated the SPARC Dynamics and Variability Project,
which will set up a model intercomparison to explore
the dynamical coupling between the stratosphere and the troposphere. The
project aims to compare in detail the climate, climate variability, and
climate-change response of standard "low-top" climate models and
stratosphere-resolving "hi-top" climate models. The means to
effectively coordinate this project with the ongoing SPARC CCMVal
and CLIVAR C20C projects will be discussed.
B. Stratospheric
Transport
Abstract B1 (Oral)
Persistence and photochemical decay of springtime total ozone anomalies
in CCMs
Susan Tegtmeier and Theodore Shepherd
The
persistence and decay of springtime total ozone anomalies over the entire extratropical midlatitudes plus polar regions is analysed using
results from the Canadian Middle Atmosphere Model (CMAM). As in the
observations, interannual anomalies established
through winter and spring persist with very high correlation coefficients above
0.8 through summer until early autumn, while decaying in amplitude as a result
of photochemical relaxation in the quiescent summertime stratosphere. We will
show that ozone anomaly persistence and decay does not depend on how the
springtime anomalies are created or on their magnitude, but reflects the
transport and photochemical decay in CMAM. The extent to which ozone anomaly
persistence and decay explains the seasonality of ozone trends in CMAM
simulations, in both hemispheres, is assessed.
Following
the same approach total ozone timeseries from further
CCMs will be used to analyse
the persistence and decay of springtime total ozone anomalies. The model
results will be compared to the observations to assess the summertime transport
and photochemical decay in the models, and the extent to which the summertime
long-term ozone trends reflect the winter/spring trends.
Abstract B2 (Oral)
O3-N2O correlations: Revisiting a diagnostic of
transport and chemistry in the stratosphere
We
revisit a widely used diagnostic of transport and chemistry in the
stratosphere, the O3-N2O correlation, with newly obtained
data from the Atmospheric Chemistry Experiment (ACE) satellite instrument. ACE
provides the first comprehensive data set for the investigation of
inter-hemispheric, inter-seasonal, and height-resolved differences of the O3-N2O
structure. Our knowledge of stratospheric O3-N2O
correlations is thereby extended and their potential for model-measurement
comparison assessed. By sub-sampling fields from the Canadian Middle Atmosphere
Model (CMAM) and comparison to the full CMAM fields, we show that the representativeness of the ACE data is somewhat restricted
and therefore may lead to biases in the interpretation of the O3-N2O
structure. Similar issues could arise in any model-measurement comparison and
hence we suggest testing the robustness of diagnostics used within CCMVal to sampling biases. However, in our case the
solution was provided by the use of area- and measurement-weighted joint
probability density functions (PDFs), which can
drastically improve the evaluation, especially in the middle stratosphere where
the correlations are not compact and therefore mainly reflect data sampling. It
is shown that PDFs provide a detailed picture of key
aspects of transport and mixing such as the tropical pipe, surf zone and polar
vortex, but also trace polar ozone loss.
Abstract B3 (Oral)
Relationships among age-of-air, chlorofluorcarbon
loss and mixing ratio boundary conditions in assessment simulations
Anne Douglass, Richard Stolarski,
Susan Strahan, Charles Jackman,
and Paul Newman
Comparison
of the distribution for stratospheric age-of-air derived from observations with
that produced by simulations is a common performance metric for atmospheric
models used to predict the future response of ozone to changes in atmospheric
composition. The realism of simulated
distributions of constituents such as chlorofluorocarbons CFCs and the inorganic
chlorine species such as HCl that are produced
through destruction of CFCs is also an important aspect of evaluation.
We
explore the relationships among the age-of-air, the CFC loss distributions, and
the fractional release, i.e. the fraction of a CFC that has been destroyed
relative to the amount initially present in an air parcel. We examine simulations using several models,
including our coupled chemistry-climate model the GEOS-CGCM, an off-line
Chemistry and Transport Model (CTM) developed through NASAs
Global Modeling Initiative GMI, and a two-dimensional CTM. There are two
implementations of both the GMI CTM and the 2DCTM, one of which produces a
realistic distribution for the age-of-air and a second with young air.
The
evolution of chlorine species in these simulations is greatly constrained by
the imposition of mixing ratio boundary conditions. The boundary conditions disconnect the
simulated chlorine evolution from the modeled loss even though this loss is
greater for the simulations with young age distributions compared to
simulations with realistic age distributions.
This analysis suggests that future assessments should use flux boundary
conditions rather than mixing ratio boundary conditions for the following
reasons. First, comparisons with
atmospheric observations such as the HALOE HCl time
series provide additional information about the fidelity of a simulation using
flux boundary conditions because the model burden and its time dependence are
not constrained. Second, the specified mixing ratios constrain recovery
scenarios. If the overturning
circulation is speeding up, a common feature of chemistry-climate models, the
CFC lifetimes decreases with time. This feedback that is missing from simulations using mixing ratio
boundary conditions.
Abstract B4 (Poster)
Comparison of the chemistry-climate model ECHAM5/MESSy with nudged tropospheric meteorology with 9 years of satellite data
Christoph Bruehl, Benedikt Steil, Patrick Joeckel,
Gabriele Stiller, and Bernd Funke
For a
direct comparison with observations the new CCM ECHAM5/MESSy was run with a
horizontal resolution of T42 and 90 layers from the surface to the mesopause with vorticity,
divergence, temperature and surface pressure nudged to ECMWF analysis data in the troposphere 700 -
200 hPa for the period 1996 to 2006. The model has an
internal QBO close to the observations. The simulation data were interpolated
in space and time to the coordinates of the observations of HALOE on UARS and
MIPAS on ENVISAT. We show timeseries and statistics
correlations and probability density functions of long-lived tracers like water
vapour, ozone, methane, HCl,
N2O and NOy in the stratosphere for
different latitudes and altitudes. We demonstrate that the CCM reproduces the
main features of the observations.
Abstract B5 (Oral)
A new method to deduce stratospheric transport times from observations
and models
Peter Hoor, Jos
Lelieveld, Hubertus Bromberger,
Harald Boenisch, Andreas Engel, Horst Fischer, Patrick Joeckel,
Benedikt Steil, and Susan Strahan
We
present a new method to determine transport times in the stratosphere which is
based on observations of N2O and CO2. So far CO2
has been used to calculate mean ages of air in the stratosphere, whereas
shorter lived trace gases like CO are used to investigate cross tropopause transport and mixing on short time-scales close
to the tropopause.
The new
approach is applicable from the extratropical tropopause deep into the overworld.
It allows in particular to quantify the mean transport
time of the younger peak in bimodal age spectra from in-situ observations. In
addition, the boundary of the subtropical barrier can be clearly defined. We
use stratospheric observations from the ER-2 and satellite platforms to
establish the method. The approach is applied and tested with ECHAM5/MESSy
model results, indicating that quasi-horizontal mixing in the model above the
tropical tropopause is too strong compared to
observations, but nevertheless upward velocities in the tropical pipe and its
boundaries are captured well.
C. Upper Troposphere / Lower
Stratosphere
Abstract C1 (Poster)
Comparison of SCOUT-O3
Markus Kunze, Christoph Bruehl,
Francesco dAmato, Martin Dameris,
Peter Hoor, Patrick Joeckel
Christian Kurz, Ulrike Langematz,
Mark Lawrence, Fabrizio Ravegnani,
Cornelius Schiller, Hans Schlager, Nikolay Sitnikov, Alexey Ulanovsky, Silvia Viciani, and
Michael Volk
We use
measurements taken on-board the Geophysica aircraft
during the SCOUT-O3 Darwin campaign in November/ December 2005 for further
evaluation of the new Chemistry Climate model (CCM) ECHAM5/MESSy. The CCM was
run with a horizontal resolution of T42 and 90 layers from the surface to the mesopause with vorticity,
divergence, temperature and surface pressure nudged to ECMWF analysis data in
the troposphere 700 - 200 hPa for the period 1996 to
2005. We focus on the tropical tropopause layer where
the vertical resolution of the model is about 600m.
To
compare the results of this CCM run with the measurements taken during the
Emphasis
of the analysis is on water vapour measured with the
instruments FISH and FLASH, ozone (FOZAN), methane (ALTO), carbon monoxide (CO_TDL),
CFC-12, CFC-11, Halon 1211 (HAGAR), nitric oxide and
total reactive nitrogen (SIOUX). Despite the large differences in temporal and
spatial resolution between the campaign measurements and the model data, the
overall agreement is quite good.
Abstract C2 (Oral)
A long-term climatology of transport processes in the TTL during NH
winter
Kirstin Krueger, Susann Tegtmeier, Franz Immler and
Markus Rex
Recent
investigations of transport processes in the tropical tropopause
region have shown that the interaction between vertical and horizontal
transport plays an important role in dehydrating air while entering the
stratosphere. Uncertainties in the formulation of vertical transport typically
limit our understanding of the dynamical processes in the tropical tropopause layer (TTL).
In this
paper we present results of multi-year calculations covering the ERA40 and
operational ECMWF analyses period. For this purpose we have developed a
different approach to better constrain the vertical velocities in trajectory
models of this region of the atmosphere: a reverse domain filling trajectory
model driven by diabatic heating rates from the ECMWF’s radiative transfer model.
We focus
on the northern hemispheric winter months which show the lowest temperatures
during the seasonal cycle and hence the lowest stratospheric water vapour mixing ratios. The analysis will focus on Lagrangian cold point temperature (LCPT), diabatic ascent and residence time within the TTL region,
which have a strong impact on reliable studies of transport processes of e.g.
very short live substances travelling from the
surface to the stratosphere. The differences which arise from this new approach
will be discussed in context with previous studies that relied on the noisy
assimilated vertical wind fields. NH winter also shows a strong interannual variability in the LCPT, which will be
investigated in more detail taking care of the most prominent dynamical
mechanism such as the influence of ENSO, QBO, solar cycle and volcanoes in
driving this variability.
Abstract C3 (Oral)
The Potential Impact of Aerosols in the Upper Troposphere on Ice Clouds
Joyce Penner, Xiaohong Liu, and Minghuai
Wang
Cirrus
clouds have a net warming effect on the atmosphere and cover about 30% of the
Earth’s area. Aerosol particles initiate ice formation in the upper troposphere
through modes of action that include homogeneous freezing of solution droplets,
heterogeneous nucleation on solid particles immersed in a solution, and
deposition nucleation of vapor onto solid particles. Here, we examine the
change in ice number concentration from anthropogenic soot originating from
surface sources of fossil fuel and biomass burning and from aircraft that
deposit their aerosols directly in the upper troposphere using a the coupled
IMPACT aerosol with the NCAR CAM3 climate model. The introduction of ice
nucleation in the upper troposphere in
Abstract C4 (Poster)
The seasonal cycle of averages of nitrous oxide and ozone in the
Northern and Southern Hemisphere polar, midlatitude,
and tropical regions derived from ILAS/ILAS-II and Odin/SMR observations
Farahnaz Khosrawi, Rolf Mueller, Mike H. Proffitt, Jo Urban, Donal Murtagh, and Hideaki Nakajima
Northern
and southern hemispheric monthly averages of ozone (O3) and nitrous
oxide (N2O) have been suggested as a tool for validating atmospheric
photochemical models. An adequate data set for such a validation study can be
derived from measurements made by satellites which in general have a high
spatial and temporal resolution. Here, we use measurements made by the Improved
Limb Atmospheric Spectrometers (ILAS and ILAS-II) which use the solar
occultation technique and by the Odin-Sub Millimetre
Radiometer (Odin/SMR) which passively observes the thermal emissions from the
Earth’s limb. Using correlations of N2O and O3, the data
are organized monthly in both hemispheres by partitioning these data into equal
bins of altitude or potential temperature. The resulting families of curves
help to differentiate between O3 changes due to photochemistry from
those due to transport. From ILAS/ILAS-II and Odin/SMR observations 1-year climatologies of monthly averaged O3 and N2O
were derived for the altitude range between 60 to 90 and -60 to -90,
respectively. A comparison between both climatologies
shows a good agreement and verifies that limited sampling from satellite
occultation experiments does not constitute a problem for deriving such a climatology. Since Odin/SMR provides measurements for the
entire hemisphere, a 1-year climatology is reported
here for the entire Northern and Southern Hemisphere from these measurements.
Further, the 1-year climatologies derived from
Odin/SMR is separated into climatologies for the low
latitudes, midlatitudes, and high latitudes. The
1-year climatologies from Odin/SMR and ILAS/ILAS-II
as well as the climatologies for the specific
latitude regions from Odin/SMR provide a potentially important tool for the
validation of atmospheric photochemical models.
Abstract C5 (Poster)
The climatic version of the MOCAGE tropospheric-stratospheric
Chemistry and Transport Model: description, evaluation and sensitivity to
surface processes
Hubert Teyssedre, Martine Michou, Hannah Clark, Fernand
Karcher, Dirk Olivi,
Vincent-Henri Peuch, David Saint-Martin, Daniel Cariolle, Phillippe Ricaud, and Francoise Chroux
We
present the climate configuration of the Météo-France
Chemistry and Transport Model, MOCAGE-Climat that,
among few models, simulates the global distribution of ozone and its precursors
(82 chemical species) both in the troposphere and the stratosphere, up to the
mid-mesosphere (70 km). Surface process emissions, dry deposition, convection,
and scavenging are explicitly described in the model that has been driven by
the ECMWF operational analyses of the period 2000-2005, on T21 and T42
horizontal grids and 60 hybrid vertical levels, with and without a procedure
that reduces calculations in the boundary layer, and with on-line or climatological deposition velocities. Model outputs have
been compared thoroughly to observations, both from satellites (TOMS, UARS,
SCIAMACHY, ODIN, MOPITT) and in-situ measurements (ozone
sondes, MOZAIC and aircraft campaigns) at climatological timescales.
In the
stratosphere, putting apart shortcomings linked to a too fast Brewer-Dobson circulation
such as too large accumulations of ozone in the lower to mid-stratosphere,
long-lived species conform reasonably to observations. However, conversions
between radical and reservoir forms of chlorine and nitrogen are not fully
resolved in the stratosphere and consequently the ozone hole is not deep
enough. Ozone in the UTLS region does not show any systematic bias, while in
the troposphere better agreement with ozone sonde
measurements is obtained at mid and high latitudes and differences with observations
are the lowest in summer.
Simulations
with the simplification of the boundary layer lead to model outputs further
away from observations up to the mid-troposphere. NOx
in the lowest troposphere are in general overestimated, especially in the winter
months over the northern hemisphere.
This might result from a positive bias in OH. Dry deposition fluxes of O3
and nitrogen species are within the range of values reported by recent
inter-comparison model exercises. The use of climatological
deposition velocities versus on-line ones impacted the most HNO3 and
NO2 in the troposphere.
The next
step will be to drive and validate MOCAGE-Climat over
longer periods with the climatological fields of the
ARPEGE-Climat atmospheric General Circulation Model.
Abstract C6 (Poster)
Sensitivity of atmospheric chemistry to the water vapour
modelling in the UTLS region
David Saint-Martin, Daniel Cariolle,
Hubert Teyssedre, Martine Michou,
and Dirk Olivi
In the
atmosphere, water vapour controls both weather and climate
and plays a central role in the stratospheric radiative
balance and in stratospheric chemistry, influencing the heterogeneous chemical
reactions that destroy stratospheric ozone. The existence of significant cross-tropopause gradients in both ozone and water vapour requires a detailed modelling
of the mechanisms which involve water vapour in the
upper troposphere and lower stratosphere region UTLS.
We
investigate the impact on chemical distributions in UTLS of both various
definition of the tropopause standard definition,
dynamic definition with potential vorticity isosurfaces, chemical definition with ozone concentrations
and various parameterisations used in troposphere ice
supersaturation scheme and in stratosphere oxidation
of methane, polar stratospheric cloud formation.
We
present results from a multi-year model simulation, using the global chemical
transport model, MOCAGE, forced by the general circulation model, ARPEGE-Climat, which provides temperature, wind and tropospheric moisture fields.
Abstract C7 (Poster)
Recent Updates of the ULAQ-CCM: inclusion of the equatorial QBO and
parameterization of UT/LS ice clouds
Giovanni Pitari, Eva Mancini, and Daniela Iachetti
The
ULAQ-CCM University of L’Aquila climate-chemistry
coupled model is a low resolution model, including an on-line microphysics code
for aerosol formation and growth. In order to improve the ULAQ-GCM ability to
simulate the interannual variability of the
stratospheric circulation, a forcing term for the quasi-biennial oscillation of
the equatorial winds (QBO) has been included in the vorticity
equation. The forcing term is calculated using the observed time-dependent
equatorial tropical winds 1960-2004, with a relaxation time of 7 days. A
comparison between observations and results is shown.
The
second major improvement of the CCM has to do with the parameterisation
for homogeneous freezing of cirrus ice particles: the effects of aerosol size
distribution changes are now taken into account. The ice particles impact on
the radiation budget is calculated using a multi-layer δ-Eddington approximation for the solar flux and scaling
pre-calculated longwave fluxes with appropriate 963T4
values for the IR part. Non-spherical ice particle are taken into account in
the effective radius calculation. The atmospheric sensitivity to cirrus ice
particles has been studied by means of subsonic aircraft emissions: increasing
water vapour and aerosols in the UT/LS, with respect
to a no-aircraft atmosphere, has the effect to perturb the ice particle
population and size distribution. Changes in cirrus cloud optical thickness
have been calculated, as well as solar and infrared radiative
forcing terms
Abstract C8 (Oral)
Diagnostics for seasonally varying and seasonally invariant transport in
the lowermost stratosphere
Susan Strahan and Peter Hoor
The
composition of the extratropical lowermost
stratosphere (LMS) is affected by seasonal variations in the strength of the
downward branch of the Brewer-Dobson circulation. In the summer, composition
changes due to increased meridional transport from
low latitudes this can be seen in long-lived tracers between
340K-380K. In contrast to the upper LMS, tracer behavior closer to the
dynamical tropopause (300K-340K) suggests that mixing
between the troposphere and stratosphere occurs in all seasons, resulting in a
mixed layer with little seasonal variation in thickness.
We
present transport diagnostics for these two regions of the lowermost
stratosphere which are based on analyses of N2O, CO, and CO2
aircraft data from the SPURT campaigns and AURA MLS CO measurements. In the
upper LMS, the degree to which a models composition is seasonally influenced by
tropical upper tropospheric air can be assessed by
comparison with seasonal changes seen in SPURT N2O observations. In
the lower LMS, the results of Hoor et al (2004),
which showed that an extratropical tropopause mixed layer 30K thick exists year-round, can be
used to gauge whether model processes realistically couple the troposphere and
stratosphere to create the mixed layer. AURA MLS, which has global coverage and
a much larger CO data set than SPURT, also supports the existence of the mixed
layer.
Abstract C9 (Poster)
Evaluation of NCAR MOZART-3 and WACCM models in the UTLS region using
tracers with different lifetimes
Simone Tilmes, Laura Pan, Douglas Kinnison, Sue Schauffler, and Rolando Garcia
The
representation of chemical transport processes that couples the upper
troposphere (UT) and lower stratosphere (LS) in CCMs
is a key component for the models to simulate future climate scenarios. Different methods have been proposed to
diagnose the model transport issues in this region. Here, we present an extension to the
diagnostics described in Pan et al., (2006), using tracers with a wide range of
lifetimes. Trace gas profiles in relative altitude and tracer-tracer
relationships are used to examine the performance of NCAR MOZART-3 and WACCM-3
models. In situ chemical tracers, including those from the Whole Air Sampler,
measured onboard NASA research aircraft during several campaigns are used to
compare with the model results. Model and observational data are compared for
tropics high tropopause, extra-tropics lower tropopause and the subtropical region, where a double tropopause often exists.
The results show that, in general, the slopes of tracers in relative
altitudes are in good agreement between models and observations. Tracer-tracer correlations indicate a general
agreement for long-lived tracers, but differences exist for shorter-lived
tracer between models and observations. Implications of these results to the
modeled age spectrum in the UTLS region and the related transport pathways will
be discussed.
Abstract C10 (Oral)
Tropical Tropopause Layer Structure in CCMs
Andrew Gettelman and Thomas Birner
The
structure and variability of the Tropical Tropopause
Layer (TTL) are analyzed in multiple global coupled chemistry climate models (CCMs), and compared to observations from ozone/radiosondes and GPS occultations.
Detailed diagnostics are performed using four-dimensional fields on model
levels from two specific CCMs – the Whole-Atmosphere
Community Climate Model (WACCM) and the Canadian Middle Atmosphere Model (CMAM).
The analysis is expanded to the CCMVal set of models.
Relationships between water vapor, clouds, ozone and the thermal structure of
the TTL are examined.
The
results indicate that the thermal structure of the TTL is well reproduced by
the CCMs. Variability of the TTL is also reproduced
by global models at the scales they can resolve. The models broadly reproduce
observed relationships between clouds and the thermal structure, and clouds and
the trace gas structure ozone and water vapor. Model deficiencies regarding
clouds and small scale structure are discussed. The results and diagnostics in
the simulations allow us to make conclusions regarding the role of transport,
radiation and convection in regulating the variability and mean structure of
the TTL.
Abstract C11 (Oral)
An approach to validate the transport of water vapour
through the tropical tropopause in chemistry climate
models
Stefanie Kremser, Markus Rex, Ingo Wohltmann, Ulrike
Langematz, and Martin Dameris
The
interaction of horizontal and vertical transport in the tropical tropopause layer (TTL) determines the distribution of
points where individual air masses encounter their minimum temperature while
they slowly ascend from the TTL into the stratosphere. The geographical
distribution of these dehydration points and the local conditions there
determine the overall flux of water vapour from the
TTL into the stratosphere. The representation of both, the geographical distribution
of the dehydration points and the local conditions there, is a measure how
realistic the water vapour transport into the
stratosphere is represented in coupled chemistry climate models (CCMs). A correct representation of these points in a model
is crucial for a correct representation of potential long-term changes of water
vapour transport into the stratosphere due to changes
in greenhouse gas concentrations. We have developed a lagrangian
framework to assess the dehydration patterns in CCMs
and will present results from two different CCMs.
Abstract C12 (Poster)
On the coupling of the MOCAGE-Climat CTM and
the ARPEGE-Climat GCM
Dirk Olivie, Hubert Teyssedre, Martine Michou, David
Saint-Martin, and Daniel Cariolle
We
present the coupling of the General Circulation Model ARPEGE-Climat with the Chemical Transport Model MOCAGE-Climat. This
coupling might allow progress in understanding the two-way interactions between
reactive gases and the climate system.
The Arpege-Climat GCM from Centre National de Recherches Météorologiques is a
state-of-the-art GCM and has been used in different climate studies. At the moment it currently contains only a
simple representation of atmospheric ozone chemistry.
MOCAGE-Climat is the climate version of the Météo-France
multi-scale Chemical Transport Model MOCAGE (see. Michou et al., this workshop) which
covers a wide range of scientific applications, and includes both tropospheric and stratospheric chemistry. Driven by operational analyses from ECMWF, it
has been compared extensively with observations for the period 2000-2005.
In a
first step towards the coupling of the GCM ARPEGE-Climat
and the CTM MOCAGE-Climat, the sensitivity of MOCAGE-Climat to the specification of the meteorological
parameters is investigated in an off-line mode applying the meteorological
forcing from the ARPEGE-Climat.
In a
second step, we will report here on the first results from the coupling between
the GCM ARPEGE-Climat with the CTM MOCAGE-Climat. The coupling
currently consists, apart from meteorological fields from ARPEGE-Climat towards MOCAGE-Climat, in
the transfer of ozone fields of MOCAGE-Climat towards
ARPEGE-Climat.
In the
future, we intend to exchange distributions of other radiatively
active gases from MOCAGE-Climat to ARPEGE-Climat. This new system should allow the study of a
significant number of interactions and feedbacks from chemistry on the climate which are essential for climate scenario studies.
Abstract C13 (Oral)
Variability and trends in global tropopause
parameters
Thomas Birner
The tropopause region is sensitive to both tropospheric
and stratospheric climate change. This makes the tropopause
region an ideal place to test and validate global chemistry climate models.
Here, variability and trends in global tropopause
parameters are analyzed as obtained from the Canadian Middle Atmosphere Model (CMAM)
for the period 1960-2100 and ERA40 1958-2001. For the current climate results
are compared to observations from radiosondes and GPS
occultations. CMAM reproduces the key features of
observed tropopause structure and variability well
including a negative trend in tropopause pressure. Tropopause temperature shows a negative trend in the polar regions and a small positive trend in the tropics.
Interestingly, the stratification around the tropopause
shows trends as well such as to lead to decreased tropopause
sharpness in future climate. Polar and tropical tropopause are coupled
through the Brewer-Dobson circulation such that an anomalously high tropical tropopause is associated with an anomalously low polar tropopause. It is shown that this represents a dominant
part of the year-to-year variability in tropopause
parameters. Furthermore, an intensified Brewer-Dobson circulation in future
climate amplifies the tropopause trend in the tropics
but attenuates it in the polar regions.
Abstract C14 (Poster)
The tropopause in the 21st century
Seok-Woo Son, Darryn
Waugh and Lorenzo Polvani
The tropopause in the 21st century is examined with CCMs. Despite the
fast recovery of stratospheric ozone, global tropopause
pressure height is found to decrease rise almost linearly in the future
climate. This trend is primarily
associated with the continuous decrease in ozone at the tropical lower
stratosphere. It suggests that the
positive correlation between the tropopause pressure
and total column ozone in the literature might be misleading. The possible impact of a stronger
Brewer-Dobson circulation in the future climate on the tropopause
pressure is also discussed.
D. Radiation
Abstract D1 (Poster)
CCMVal Radiation comparison test designs
Piers Forster
This will illustrate the webpage
where modelling groups can register and download test
profiles to participate in the offline comparison of radiative
transfer codes. This will concentrate on simulations of the stratospheric
temperature response. The aim is to have representation from ALL the CCMval models and several line-by line models.
Abstract D2 (Poster)
Attribution studies with CCMval model temperature change in the stratosphere
Piers Forster and John Austin
Temperatures changes in the
stratosphere of the CCMval models are due to a
variety of effects. This work uses offline radiative
transfer calculations and fixed dynamical heating models to try to establish
cause and effect for the models own temperature response.
Abstract D3 (Poster)
Clear
sky UV simulations in the 21st century based on CCM predictions
K. Tourpali, A.F. Bais, A. Kazantzidis, N. Butchart, C. Brühl, M P. Chipperfield, M. Dameris, V. Eyring, M.A. Giorgetta, U. Langematz, E. Mancini, E. Manzini,
G. Pitari, E. Rozanov
Future solar UV radiation levels will depend on the evolution of various
factors, known to influence the propagation of UV radiation in the atmosphere.
Some of these factors, such as ozone, clouds and surface reflectivity are
included in coupled Climate Chemistry Model (CCM) output, whereas the
prediction of future aerosol levels and their optical characteristics,
important for UV radiation, is presently not feasible. Under clear skies, the
most important factor for UV-B radiation is stratospheric ozone, followed by tropospheric ozone and aerosols.
In this preliminary study we have used monthly mean total ozone (TOZ) as
provided by CCMs taking part in SCOUT-O3 Activity 1.
TOZ data are an outcome of simulations run under the REF2 and SCN2 scenarios,
consistent with the reference simulations proposed by CCMVal.
TOZ is then used as
input to a radiative transfer model (LibRadTran) for the simulation of the corresponding future
UV irradiance levels, presented here as
time series of monthly erythemal irradiance
received at the surface during local noon, with a time span following the CCM
output.
E. Stratospheric Chemistry and
Microphysics
Abstract E1 (Oral)
Simple measures of ozone depletion in the polar stratosphere
Rolf Mueller, Jens-Uwe
Grooss, Carsten Lemmen, Daniel Heinze, Martin Dameris, Greg Bodeker
Simple
measures of polar chemical ozone loss are frequently used that are solely based
on measurements of total colum
ozone. One of the common measures is monthly mean column ozone poleward of a latitude of 63o
in spring. For the
Abstract E2 (Poster)
Further Developments of the CCM E39C - Documentation of Significant
Model Improvements
Andrea Stenke, Martin Dameris, and Volker Grewe
An
ensemble of long-term transient simulations 1960-2020 with the coupled
climate-chemistry model (CCM) E39C have been analysed
(Dameris et al., 2005, 2006) and evaluated in a
number of extra scientific investigations (e.g. Erbertseder
et al., 2006; Eyring et al., 2006; Steinbrecht et al., 2006). On the one hand it has been
demonstrated that E39C is able to reproduce important features of stratospheric
dynamics and chemistry, but on the other hand significant deficiencies have
been identified which must be eliminated to provide a more reliable prediction
of the evolution of stratospheric dynamics and chemistry.
In an
updated version of E39C, i.e. E39C-A, a variety of model developments have been
implemented: The most important advancement concerns the change of the
advection scheme from a semi-Lagrangian approach by Rasch and Williamson (1994) to the full Lagrangian
transport scheme ATTILA (Reithmeier and Sausen, 2002). Since ATTILA is a numerically non-diffusive
scheme, it is able to maintain steeper and therefore more realistic gradients
than the semi-Lagrangian scheme. Furthermore, a parameterisation to consider bromine chemistry (pers. comm. M. Rex, 2006) has been introduced into the
model and improved net heating rates has been used to describe impact of large
volcanic eruptions as realistic as possible (Stenchikov
et al., 2006).
Results
of a new transient model simulation 1960-2004 with the updated model version
E39C-A are presented and specific improvements are discussed in detail: The Lagrangian transport scheme leads to a significant
improvement of the simulated water vapour
distribution which in turn results in a significant reduction of cold bias in
the extratropical lowermost stratosphere and a much
better representation of stratospheric wind variations. Furthermore, simulated
tracer distributions in the stratosphere are improved. For example, the
vertical distribution of stratospheric chlorine is now in agreement with
analyses derived from observations and other CCMs
which leads to a better assessment of ozone
destruction. Finally, the simulated response of stratospheric temperatures and
water vapour concentrations on large volcanic
eruptions agrees well with observations.
Abstract E3 (Oral)
Sulfur injections into the stratosphere to alter the atmospheric
chemical and dynamical state
Thomas Peter, Patricia Kenzelmann, Peter
Spichtinger, Stephan Fueglistaler, Martin Schraner, and Eugene Rozanov
In the
past large eruptions of tropical volcanoes led to a net cooling of surface temperatures.
The cooling is due to enhanced stratospheric sulfur aerosols, which shield a
part of the short-wave radiation coming from the sun. Could this effect help to
find a way to reduce the effects of global warming? Recently Crutzen suggested investigating the possibility of
performing a geoengineering project in which yearly
1-2 Tg of sulfur are
injected into the stratosphere, which is 10-20% of the stratospheric sulfur
loading caused by the
Such a
project differs in some crucial features from a natural experiment like the
eruption of
Steady
state runs with the chemistry climate model SOCOL suggest a significant impact
on stratospheric chemistry and dynamics. The lower stratosphere would warm
considerably and the polar vortex would intensify. This results in a feedback
to the troposphere, where during wintertime in some regions a considerable
warming takes place. We will also discuss the problem of polar winter warming
under conditions of enhanced stratospheric aerosol loading, and from there
attempt an overall evaluation of the effects of the geoengineering
proposal on stratosphere and troposphere.
Abstract E4 (Withdrawn)
An Evaluation of Chemical Loss of Extra-Polar Ozone within CCMs: Overview
Ross Salawitch
Chemical
loss of ozone outside of the polar regions is
controlled by a series of catalytic reactions involving HOx,
NOx, ClOx, and BrOx radicals. The total rate of ozone loss and relative
contribution from each family to total loss are sensitive to a variety of
factors, including altitude, latitude, temperature, and aerosol loading. I shall examine the representation of
chemical loss within CCMs by comparing a variety of
comparing a variety of factors from the models to data: the representation of
long-lived radial precursors e.g., NOy vs N2O, Cly vs CFC-11, Bry vs CH3Br the partitioning within radical
families e.g., NOx/NOy, ClOx/Cly,
BrOx/Bry the abundance of HOx
total and partial column BrO and, the fractional
contribution to total ozone loss from the various chemical families. Recent
satellite and balloon data will be featured throughout. Strengths and weaknesses of the comparisons will
be noted, as appropriate. I shall conclude by suggesting future improvements
both in output model diagnostics and CCM capability.
Abstract E5 (Poster)
First ECHAM5-MESSy1 simulation results peformed
with a new PSC parameterisation and comparison with
MIPAS-ENVISAT data
Roland Ruhnke, Ole Kirner, Michael Hoepfner, and
Gabi Stiller
Polar
stratospheric clouds (PSCs) such as STS, NAT, and ice
play a major role in polar ozone depletion: directly via the activation of
chlorine reservoirs at the surface of the PSCs and
indirectly via denitrification delaying the
deactivation of active chlorine in polar spring.
Despite
this importance of PSCs the representation of PSC
microphysics is rather poor in current CCMs. Here we
present the first results of a multi-year simulation of ECHAM5-MESSy1 from
November 2002 through spring 2005 performed with a new PSC parameterisation
for the CCM ECHAM5-MESSy1 based on the efficient growth and sedimentation
algorithm of van den Broek et al. (2004). The results
will be compared to ECHAM5-MESSy1 simulation results obtained by using the
standard thermodynamical PSC scheme. In addition, the
ECHAM5-MEssy1 results with the new PSC scheme will be analysed
with respect to the occurrence and composition distinguished between NAT, ice
and STS of PSC fields and compared to PSC measurements of the MIPAS-ENVISAT
experiment Hoepfner et al., (2006).
Abstract E6 (Poster)
Examining tropospheric seasonal cycle of chlorofluorobarbons using GEOSCCM with emission-based
boundary conditions
Qing Liang, Richard Stolarski,
Anne Douglass, Paul Newman, Eric Nielsen, and Steven Pawson
To more
accurately predict the impact of climate change on atmospheric circulation and
lifetimes of long-lived ozone depleting substances, and therefore future ozone
recovery, it is desirable to switch from the current commonly adopted mixing
ratio-based forcings to emission-based forcings in general circulation models GCMs.
As a first step of this model transition, we have conducted a 45-year 1960-2005
emission-based simulation of CFC-11, CFC-12, and CFC-113 using the GEOS
CCM. CFCs are released at the surface
based on the WMO/UNEP A-1 scenario emissions with a regional distribution, and
destroyed in the stratosphere through photolysis and reaction with O1D. We evaluate CFC emissions and the model
simulation by comparing the model results with surface CFC observations at
AGAGE sites. The simulation agrees with the observed mixing ratios of CFC-11
and CFC-12, reflecting a good estimate of emissions as well as atmospheric
lifetimes. The simulated CFC-113 mixing
ratios show a high bias, implying an overestimate in emissions and/or an
overestimate of loss rate. Surface CFCs
at many AGAGE sites show seasonal cycles with varying amplitudes and seasonal
maxima/minima. We repeat the simulation
for 1995-2005 with two additional suites of tagged CFC tracers
three tropospheric tracers to track recently emitted
CFCs, and three stratospheric tracers to track CFCs that have been at some time
in the stratosphere. Using the tagged tracers, we will analyze the seasonal
cycle of CFCs at several AGAGE stations and quantify the contribution of
stratosphere-to-troposphere transport and tropospheric
transport for seasonal variations of CFCs in the troposphere.
Abstract E7 (Poster)
Is the major fraction of polar stratospheric ozone loss due to an
unknown mechanism?
Markus Rex, Robyn Schofield, Timothy Canty, and Ross J. Salawitch
Uncertainties
in the photolysis cross sections of ClOOCl have long
been a limiting factor in our theoretical understanding of the rate of polar
stratospheric ozone losses. Previous work suggested that values slightly larger
than current recommendations, which are based on laboratory measurements,
result in improved agreement between model calculations of polar stratospheric
ozone loss rates and observations while at the same time also leading to
improved agreement between observations of the diurnal variation of ClO and model calculations of this species. But new
laboratory work on the cross sections of ClOOCl
suggest that its photolysis under polar stratospheric winter/spring conditions
is nearly an order of magnitude slower than what would be required to explain
the observations of ozone loss and ClO in the
atmosphere and a factor of six slower than a value based on the current
recommendations. We show the impact of these new results on our understanding
of polar ozone chemistry.
For
typical Arctic conditions calculated ratios of ClO/ClOx
decrease by about a factor of two. The ozone loss rate by the ClO-dimer cycle, so far believed to be the most efficient
ozone loss cycle, drops by about a factor of four and the loss rate by the
coupled ClO-BrO cycle by nearly a factor of two.
Overall ozone loss rates calculated based on the known ozone loss mechanisms
drop by a factor of two to three and become much smaller than observations.
Also the calculated levels of ClO become much smaller
than those observed in the stratosphere. These results suggest that a major
fraction of the observed ozone loss in the polar stratosphere is due to a
currently unknown mechanism - a major challenge of our fundamental
understanding of the polar stratospheric ozone loss process.
We will
discuss potential new chemistry that would lead to improved agreement between
calculations of ozone loss and ClO diurnal variations
with in-situ observations in the stratosphere.
Abstract E8 (Oral)
The impact of mixing across the polar vortex edge on ozone loss
estimates: Implication for the validation of CCMs
Jens-Uwe Grooss, R. Muller, P. Konopka, H.-M.
Steinhorst, A. Engel, T Mbius, C.M Volk, and T. von Clarmann
Published
estimates of accumulated Arctic polar ozone loss show a compact linear relation
with the temperature-based proxy VPSC. It has been suggested to use
this relation for the validation of CCMs. The
underlying methods e.g. Vortex average method/Match however do not take into
account the mixing across the vortex edge.
We show
for the winter 2002/03 that significant mixing across the vortex edge did occur
and that it can be modeled accurately by the Chemical Lagrangian
Model of the Stratosphere. Observations of inert tracers in-situ from HAGAR on
the Geophysica aircraft and also remote from MIPAS
IMK on ENVISAT can be reproduced well. CLaMS is even able to reproduce a small vortex remnant that was
isolated until June 2003 and was observed in-situ by a balloon-borne whole air
sampler.
From this
simulation, the impact of mixing across the vortex edge on ozone loss estimates
is evaluated. The impact may be two-fold:
1 The time integration of the vortex average ozone loss must
be corrected for the export of ozone-depleted air into mid latitudes. For the
winter 2002/03, the accumulated ozone loss without this correction is 39%
larger than the simulated vortex average column ozone loss.
2 A continuous import of air masses with lower ozone mixing
ratios can mimic enlarged ozone loss rates for the Vortex Average estimate, but
also for the Match approach even though it aims to avoid air masses which are
influenced by mixing. Both effects yield an over-estimation of ozone loss in
the Match and vortex-average methods.
For
better validation of the ozone loss and transport in CCMs
we suggest comparing the simulated VPSC/O3 relation with
caution, and also (a) to compare with observations of ozone mixing ratio and
other inert tracers like CH4 or N2O in equivalent
latitude and potential temperature coordinates e.g. Grooss
and Russell, 2005 and (b) to compare ozone column with meaningful averages in
equivalent latitude coordinates (cf. contribution of Muller et al).
Abstract E9 (Oral)
Evaluation of Chemical Polar Ozone Loss in the Lower Stratosphere within
CCM Models
Simone Tilmes, Rolando R. Garcia, Douglas E. Kinnison, Rolf
Mueller, Ross Salawitch, Markus Rex, Daniel R. Marsh, and Fabrizio Sassi
The
simulation of the evolution of ozone in polar regions
in different CCMs still indicates significant
differences. Especially, discrepancies exist for the simulations of Arctic
conditions among different models
Here, we
will discuss differences of these diagnostics, and the derived relationship
between chemical ozone loss and PACl, between all CCMs that have submitted the requisite model output to the
data archive and observations. Using NCAR’s Whole
Atmosphere Community Climate Model (WACCM), we will show that the described diagnostics
and the strength and sharpness of the polar vortex edge in the model are
important factors that influence heterogeneous processes in the polar vortex.
We will discuss the importance of horizontal resolution for polar processes in
the model.
Abstract E10 (Poster)
Evaluation of NOy Chemistry in CCMVAL Models
Wenshou Tian and
Martyn Chipperfield
We have
used output from CCMVal models to test their
representation of stratospheric NOy chemistry. We
will show comparisons with satellite climatologies
and tracer-tracer correlations. Large differences exist between the models.
F. Natural Variability
Abstract F1 (Oral)
Coupled chemistry climate model simulations of the solar cycle in ozone
and temperature
John Austin, Eugene Rozanov, Klairie Tourpali, et al.
The
results from new simulations of coupled chemistry climate models are examined
for the presence of the 11-year solar cycle in ozone and temperature. In
contrast to most previously published simulations, the new simulations are in
better agreement with satellite observations of the vertical profile of the
ozone response, particularly in low latitudes where the observational signal
can be more firmly established. It is found that this improved agreement occurs
by incorporating variability only in the solar fluxes in the models and that
the upper atmospheric effects of energetic particles are not important for the
low latitude ozone signal. The results also suggest that the presence of the
quasi biennial oscillation is not necessary to simulate the observed low
latitude minimum in lower stratospheric ozone response. Comparisons are also
made between model simulations and total column ozone. As in previous studies,
the model simulations agree well with observations. However, a substantial difference
exists between the observed signal for the period 1960-1980 and for the period
1980-2000. This is reproduced by those models which cover the full temporal
range, and it is shown that the difference between the solar cycles in the
simulations is due almost entirely to ozone changes below 50 hPa. Possible reasons for the tropical ozone minimum, and for the difference in ozone response for
different solar cycles are discussed in addition to the impacts of the solar
response on the troposphere.
Abstract F2 (Oral)
The Role of the QBO in Simulating the Solar Signal in the Atmosphere
Katja Matthes, Rolando Garcia, Dan Marsh, and
Anne Smith
The
11-year solar cycle has an impact on the chemical, thermal, and dynamical
structure of the atmosphere. Observational and modeling studies have shown that
direct radiative changes in the upper stratosphere
can lead to indirect dynamical changes throughout the atmosphere. However, the
understanding of the interaction with the equatorial stratospheric Quasi-Biennial
Oscillation is still a challenging topic. Discrepancy exists in separating the
solar and QBO signals in observations partly due to the short length of
existing data sets. Therefore modeling studies are useful to enhance the
understanding of the underlying physical mechanisms.
To
understand the response of the middle atmosphere to the 11-year solar cycle and
its possible transfer to the troposphere a comprehensive set of experiments
made with a state-of-the-art chemistry climate model that incorporates the
whole atmosphere up to the thermosphere will be investigated. Especially the
role of an externally prescribed stratospheric QBO in influencing the 11-year
solar cycle signal in NCAR’s Whole Atmosphere
Community Climate Model WACCM3 will be discussed.
The set
of experiments with WACCM3 consists of different perpetual condition
experiments solar cycle only or solar cycle and QBO as well as long-term
110-year sensitivity experiments, in which only a realistic time varying solar
cycle, only a synthetic, time varying QBO or both the solar cycle and the QBO,
were included. In all simulations the sea surface temperatures had a repeating climatological seasonal cycle and the greenhouse gases were
set constant to 1995 conditions.
Abstract F3 (Oral)
Winter Climate Response to ENSO in three chemical-climate models
Andreas Fischer, Drew Shindell,
Michel Bourqui, Barbara Winter, Eugene Rozanov, and Stefan Bronnimann
El Nino
/ Southern Oscillation (ENSO) plays an important role
in interannual climate variability. Yet the impacts
of ENSO on chemical climate variability in the northern stratosphere are not
completely understood to date. Knowledge about the performance of
chemistry-climate models CCMs in reproducing past
ENSO events is therefore highly relevant both as a test for current climate
models as well as to improve our current understanding of the mechanisms
linking ENSO with the northern stratosphere.
Here we
present a model-intercomparison of three CCMs SOCOL, IGCM-FASTOC, GISS that simulated the El Nino
event of 1940/41 and the La Nina event 1975/76. SOCOL is a middle atmosphere
version of ECHAM4 MPI,
The
model-intercomparison will entail a detailed analysis
of the model-response to the winter difference of El Nino (1941) and La Nina (1976)
in the Northern Hemisphere stratosphere. We will analyse
ozone, temperature, geopotential height, and zonal
wind as well as Eliassen-Palm (EP) flux and compare
model results with observational databases.
Abstract F4 (Poster)
Delay of the Antarctic polar vortex breakup time in the year 1980-1999
due to ozone depletion simulated by the CCSR/NIES CCM with the CCMVal-REF1 and
-REF2 scenarios
Hideharu Akiyoshi, Libo
Zhou, Kei Sakamoto, Motoyoshi Yoshiki,
Tatsuya Nagashima, Masaaki Takahashi, Jun-ichi Kurokawa, Masayuki Takigawi, and Takashi Imamura
The
delay of the Antarctic polar breakup time in the year 1980-1999 is examined
using the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA40 data
and the output of Chemistry-Climate Model (CCM) calculations. The CCM used in
this study is the Center for Climate System Research/National Institute for
Environmental Studies (CCSR/NIES) CCM. The CCM calculations follow the REF1 and
REF2 scenarios for Chemistry-Climate Model Validation Activity CCMVal.
The CCM
simulates the ozone hole development from 1982 to 2000
observed by Total Ozone Mapping Spectrometer (TOMS), although the year-to-year
variation is different from the observation because of the internal variability
of CCM and the ozone mass deficit is smaller than the observation. The ERA40
data shows a delay trend of the breakup time of the Antarctic polar vortex in
the period 1980-1999. The delay is simulated by the two ensembles of the CCM
calculations, in which long-term variations of the solar 11-year cycle, the
quasi-biennial oscillation (QBO), and the volcanic eruptions El Chichon and Pinatubo are included following the REF1
scenario of CCMVal. A CCM calculation without these
long-term variations the REF2 scenario of CCMVal
shows a larger delay trend of the breakup time than that of the REF1
simulation. The wave flux from the troposphere to the stratosphere and its
deposition in the lower stratosphere are also examined. The vertical component
of the Eliassen-Palm (EP) Flux at 100 hPa and the EP flux divergence at 50-150 hPa calculated from ERA40 data shows an acceleration trend
for earlier polar vortex breakup time in the period 1980-1996, and those
calculated from the three CCM calculations show almost no trends. All these
results suggest that the delay of the breakup time of the Antarctic polar
vortex in the period 1980-1999 is largely caused by the ozone loss in the
Antarctic lower stratosphere.
Abstract F5 (Poster)
Total column water vapour trends from GOME and SCIAMACHY
satellite measurements - A new data set for the evaluation of chemistry-climate
model simulations
Sebastian Mieruch, Stefan Noel, Heinrich Bovensmann, and John
Burrows
Satellite
observations provide us today with high quality and high resolution global data
and are well suited for monitoring of environmental parameters as well as for
comparison with model calculations.
Global
water vapour total column amounts have been retrieved
from spectral data provided by the Global Ozone Monitoring Experiment (GOME)
flying on ERS-2 which was launched in April 1995 and the SCanning
Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) onboard ENVISAT launched in March
2002.
For this
purpose the Air Mass Corrected Differential Optical Absorption Spectroscopy (AMC-DOAS)
approach is used. The combination of the data from both instruments, which
requires special treatment at the interchange, provides us with a long-term
global data set spanning already now more than 11 years with the possibility of
extension up to 2020 by GOME-2 on Metop. Thus this
data set is well suited for a trend analysis.
Using
linear and non-linear methods from time series analysis as well as standard
statistics the trends of water vapour contents and
their errors are calculated. Several factors affecting the trend such as the
length of the time series, the magnitude of the variability of the noise and
the autocorrelation of the noise are investigated. Special emphasis lies on the
calculation of the statistical significance of the observed trends which reveal
local significant changes, decrease as well as increase, of water vapour concentrations distributed over the whole globe.
The data
set is suitable to test the ability of coupled chemistry-climate models, CCMs, to reproduce total column water vapour
trends in the past. We plan to compare the trend analysis to results of the CCMVal simulations.
G. Long-Term Changes in the
Stratosphere
Abstract G1 (Poster)
Coupled Chemistry-Climate Model Assessment and Projections of
Stratospheric Ozone in the 21st century
Veronika Eyring, Darryn W.
Waugh, Greg E. Bodeker, Neal Butchart,
Eugene Cordero and CCMVal Team
Simulations
of the recent past from thirteen coupled chemistry-climate models CCMs participating in the CCM Validation Activity for SPARC
CCMVal are evaluated to provide guidance for the
interpretation of ozone projections made by the same CCMs.
Several different diagnostics are used to evaluate temperature, trace species
and ozone in the models. The core period of the evaluation is from 1980 to 1999
but long-term trends are compared for an extended period 1960-2004. Most CCMs show reasonable agreement with observed total ozone
trends and variability on a global scale, but a greater spread in the ozone
trends in polar regions in spring. Global long-term
stratospheric temperature trends are in reasonable agreement with satellite and
radiosonde observations. The simulated ozone
evolution in the 21st century in the CCMs is mainly
determined by decreases in halogen concentrations and continued cooling of the
global stratosphere due to increases in greenhouse gases. Differences in stratospheric
inorganic chlorine (Cly) among the models are key to
diagnosing the inter-model differences in simulated ozone hole
recovery.
Abstract G2 (Oral)
Inorganic Chlorine and Ozone Recovery in CCMs
Darryn Waugh, Veronika Eyring,
and CCMVal Team
Changes
in stratospheric chlorine play a major role in long-term changes of ozone, and
it is important that coupled chemistry-climate models CCMs
correctly model the time evolution of stratospheric chlorine. We examine here
the evolution of stratospheric inorganic chlorine (Cly)
and ozone (O3) in the CCMs participating
in the CCM Validation Activity. It is found that there are substantial
quantitative differences between the simulations of Cly,
with corresponding differences in the simulated ozone. In the polar lower
stratosphere the peak Cly varies from less than 2 ppb
to over 3.5 ppb, and the date at which the Cly
returns to 1980 values varies from before 2030 to after 2050. There is a
corresponding large range in the timing of recovery of Antarctic ozone back to
1980 values, and models with an earlier Cly recovery
generally have an earlier ozone recovery. This agreement indicates that the
differences in Cly between models are key to diagnosing the inter-model differences in simulated
ozone recovery.
Abstract G3 (Poster)
Coupled chemistry climate model simulations of stratospheric temperature
John Austin, Piers Forster, John Wilson, et al
Temperature
results from the CCMval simulations for the past are analysed using multi-linear regression including a trend,
solar cycle and volcanic aerosol terms. The climatology of the models for
recent years is in good agreement with observations for the troposphere and
gradually diverge from each other in the stratosphere.
Overall, the models agree better with observations than previous assessments.
As a function of latitude and pressure, the model trends vary substantially
from model to model, although all models show consistent features of overall
cooling peaking near 1 hPa, and statistically
significant cooling trends from generally the lower stratosphere upwards in the
low and middle latitudes. Several models also indicate statistically
significant cooling in the lower stratosphere over the polar
regions. Many models also show statistically significant warming in the
troposphere. The temporal variation in the global average temperature in the
lower stratosphere is also compared with radiosonde
observations, indicating clear warming signals during the volcanic eruptions,
superimposed on an overall cooling. The model response to the volcanoes varies
by about a factor of 2 with several models substantially overpredicting
the observed response during the 1980s and 1990s. Comparison of the globally
averaged temperature simulated by the models is generally in agreement with
satellite data over much of their range, except near 5 hPa
and 0.5 hPa. Model trend comparisons are also shown
for the polar spring.
Abstract G4 (Poster)
Understanding the Changes of Stratospheric Water Vapor in GEOSCCM
Simulations
Luke Oman, Darryn
Waugh, Richard S. Stolarski, Steven Pawson, Anne R. Douglass, Paul Newman, and Eric J. Nielsen
Stratospheric
water vapor is a very important part of the chemistry of the upper atmosphere.
Therefore, any changes in the long term trend in the amount of water vapor
could be significant. In this context, we examine the period of 1950-2100 in
simulations using the GEOS coupled chemistry/climate model CCM to understand
the forcings responsible for interseasonal
to decadal scale variability in stratospheric water vapor. This will allow us
to understand the relative impacts of changes in tropical sea surface
temperatures, ozone, and meridional heat flux in
determining the temperature response over tropical tropopause
layer. It will be shown that this model does an excellent job reproducing the
current mean state of stratospheric water vapor as compared to
observations.
We will
show that in GEOSCCM changes in tropical temperatures at 85 hPa,
which is the cold point tropopause, can
quantitatively explain most of the interannual
variations in stratospheric entry water vapor.
In contrast, the trend in 100 hPa tropical
temperature is much larger, showing that examining 100 hPa
temperatures might not be appropriate for analysis of changes in stratospheric
water vapor. Over the 150 year simulation the cold point temperatures, and
hence stratospheric entry water vapor, are very stable, and most of the trend
in extra-tropical stratospheric water vapor is due to changes in methane.
Abstract G5 (Poster)
Transient simulations of climate changes in the upper stratosphere and mesosphere
Andreas I. Jonsson and Victor I. Fomichev
The
Canadian Middle Atmosphere Model (CMAM) is a coupled chemistry-climate model (CCM)
which extends from the surface up to about 95 km. It includes realistic
implementations of the major physical and chemical processes necessary to
represent the complexity of interactions throughout the model domain. An
ensemble of three model simulations for the period 1960 to 2100 has been
performed to investigate the atmospheric response to transient forcings in sea surface temperatures, CFCs and greenhouse
gases, including CO2, CH4 and N2O. This paper
focuses on model results in the upper stratosphere and mesosphere. In
particular, we analyze simulated trends in temperature, ozone and water vapor,
and compare with available long-term observations.
While
enhanced CO2 acts to cool the middle atmosphere, temperature trends
are modulated by long-term changes in ozone concentrations: CFC-induced ozone
depletion in the past has lead to enhanced cooling whereas ozone recovery in
the future will reduce the CO2 effect. Also, due to the temperature
dependency of gas-phase ozone chemistry the colder temperatures in the future
will lead to a super recovery of ozone.
Water vapor increases, mainly induced by increasing CH4, can
cool the atmosphere either directly through enhanced long-wave cooling or
indirectly through reduced ozone concentrations resulting from enhanced HOx catalytic cycling. For an improved understanding of the
relevance of the different processes we analyze changes in shortwave and longwave heating rates.
Abstract G6 (Poster)
Validation of the new version of the CCM SOCOL against satellite data.
Eugene Rozanov, Martin Schraner, Andreas Fischer, Vladimir Zubov,
Patricia Kenzelman,
Tatiana Egorova, Werner Schmutz,
and Thomas Peter
The
comparison of the CCM SOCOL results with observations and other models revealed
some weaknesses of the model. A number of modifications of the transport and
chemical part of the model were implemented to overcome the discovered
problems. We have applied the family transport approach in the transport part
of the code to prevent excessive destruction of the active chlorine in the
high-latitudes lower stratosphere during winter season. The mass-fixer scheme
for the ozone was modified to avoid artificial ozone loss during the early
winter over the southern high-latitudes. We have also updated the chemical
solver, description of the heterogeneous chemistry and the properties of the
stratospheric sulfate aerosol. To fix the overall overestimation of the
stratospheric water vapor we have parameterized the removal of the water vapor
in the lower tropical stratosphere caused by freezing and sedimentation of the
ice particles. We have carried out 29-year long model run covering 1976-2004
and compared the results of the new SOCOL version with available observations.
The results of the comparison showed substantial improvement of the model
performance especially over the polar areas. These results will be presented in
details together with brief overview of further model development.
Abstract G7 (Oral)
Quantifying key sensitivities within CCMs as a
means of CCM validation
Greg Bodeker, Petra Huck, Hamish Struthers,
Irene Cionni, Dan Smale,
Birgit Hassler, Tatiana Egorova,
Eugene Rozanov, and Adrian McDonald
The
climate sensitivity parameter, the change in global mean surface temperature
corresponding to a given change in radiative forcing,
is a useful diagnostic quantity for comparing global climate models with each
other and with observations. In an analogous manner, in this study two
semi-empirical equations were developed which relate the conversion of inactive
Equivalent Effective Antarctic Stratospheric Chlorine (EEASC) to activated
EEASC, and then the rate of ozone destruction to activated EEASC. The
coefficients from these equations capture key sensitivities in the real
atmosphere which can also be easily computed in CCMs.
We propose that comparisons of these sensitivities may provide new insights
into potential sources of differences in CCM projections of Antarctic ozone
depletion.
The
first semi-empirical model, regressed against MLS observations of ClO, was used to calculate the total mass of activated
EEASC through a given Antarctic season when provided with stratospheric
temperature fields and a definition of the vortex edge. The equation is a first
order differential equation that results in two coefficients and relates the
tendency time rate of change of activated EEASC to:
1 unactivated EEASC multiplied by
PSC area multiplied by sunlight hours, and
2 a decay in activated EEASC to account for conversion back
to reservoir species.
The
second semi-empirical model, regressed against 20
years of Antarctic ozone mass deficit OMD observations, results in four
coefficients and relates the time rate of change in Antarctic OMD to:
1 the mass of activated EEASC as derived from the first
equation including a non-linear dependence,
2 strictly seasonally dependent increases in ozone within
the vortex, and
3 to mid-latitude planetary wave activity to account for
year-to-year differences in diabatic descent and/or
dynamical resupply of ozone.
The OMD
is a robust measure of the severity of Antarctic ozone depletion and these two
semi-empirical models are able to explain much of the intra- and inter-annual
variability observed in daily OMD time series. The paper presents a derivation
of the 6 coefficients, shows how they quantify key sensitivities in reality,
and discusses how they may be used for process oriented validation of CCMs.
Abstract G8 (Poster)
A comparison of temperature trends from CCMs
and AOGCMs
Eugene Cordero and Veronika
Eyring
Simulations
of 20th and 21st century temperatures from coupled chemistry-climate models (CCMs) used for the 2006 WMO/UNEP Ozone Assessment and
atmosphere ocean general circulation models (AOGCMs)
used for the Intergovernmental Panel on Climate Change Fourth Assessment Report
are compared to understand the role of interactive chemistry on temperature
variability and trends. Climatological mean
temperatures from the two model datasets are compared with observations to
investigate annual and seasonal biases. Trend calculations between
1960-2000 are then examined to determine if CCMs
are better constrained to observations in the stratosphere and upper
troposphere than the AOGCMs. Trends in the 21st
century are also investigated, and the relationship between these results and
the simulated ozone and water vapor evolution will be discussed.
Abstract G9 (Poster)
Validation of the LMDZ-INCA climate chemistry model
Fabrice Jegou, Didier Hauglustaine, Francois Lott,
Jean-Pierre Pomereau, Franck Lefevre, and Slimane Bekki
LMDZ-INCA
is a coupled Climate-Chemistry Model developed to study the interactions
between dynamical, physical and chemical processes in the troposphere and
stratosphere and in particular the upper troposphere and lower stratosphere.
The model uses 50 vertical levels from the surface to 76 km and a horizontal
resolution of 2.5o in latitude and 3.75o in longitude. 63
chemical species are treated with this model.
Our
first reference simulation was to reproduce the 1980-2006 period REF2 CCM-Val
simulation. This simulation is designed to reproduce the well-observed period
of the last 25 years during which ozone depletion is well recorded, and allows
for a more detailed investigation of the role of natural variability and other
atmospheric changes important for ozone balance and trends. This transient
simulation includes all anthropogenic and natural forcings
based on changes in trace gases, volcanic eruptions, and sea surface
temperatures SSTs. SSTs in this run are based on observations.
In this
study, we evaluate LMDZ-INCA by making comparisons with satellites and
ground-based measurements. We use the UARS observations provided by the CLAES
1991-1993, HALOE, and MLS 1991-2005 instruments. To complete the 2000s period,
we use the Odin SMR and OSIRIS 2001-2006 measurements. We also compare the
LMDZ-INCA ozone field with the TOMS observations. The NDACC network
observations give us the opportunity to make comparisons up to the stratosphere
through lidar and micro-wave profiles. Finally we use
the HIBISCUS campaign to improve our understanding of the H2O
stratospheric concentration.
The
reference simulation is performed within the European project SCOUT O3 Activity
1 Ozone, climate and UV predictions. This reference simulation is also carried
out in the framework of the ongoing CCMval activity
established within the SPARC project.
Abstract G10 (Oral)
Diagnostic tests of polar ozone recovery
Paul Newman, E.R. Nash, A.R. Douglass, J.E.
Nielsen, S. Pawson, and R.S. Stolarski
Correctly
reproducing polar ozone losses in CCMs is technically
challenging. First, the zeroth order dynamical processes must be correctly
reproduced. This includes both
temperature cold enough to form PSCs and a polar
vortex that isolates the polar latitudes from mid-latitude influence. Second, the first order mean poleward and downward Brewer-Dobson circulation must be
reproduced. Third, direct heterogeneous
reactions and catalytic cycles must be correctly represented. Finally, the degradations of fully
halogenated chlorofluorocarbons must be correctly simulated. In this work we show estimates of dynamical
and chemical parameters from the GSFC GEOS-CCM that provide tests of the
dynamics, transport, and chemistry for correctly simulating polar ozone
loss. We will also show the recovery
predictions of the GSFC-CCM.
Abstract G11 (Oral)
The CMAM transient simulations for CCMVal:
Analysis of long-term changes in ozone
David Plummer, Stephen Beagley,
Krill Semeniuk, John Scinocca,
Jack McConnell, and Ted Shepherd
The
Canadian Middle Atmosphere Model (CMAM) has been used to produce a three-member
ensemble of transient simulations charting the evolution of the stratosphere
from 1950 to 2100. To first-order, changes in total column ozone from the
recent past out to the end of the 21st century displays the effects of changing
chlorine loading, cooling of the upper stratosphere and dynamical changes
associated with changes in wave-forcing from the troposphere. As chlorine
loadings decrease CMAM projects a super-recovery in mid-latitude ozone columns,
with a stronger recovery in the Northern Hemisphere, while tropical ozone is
projected to remain below pre-1975 levels.
The chemical and dynamical effects controlling these changes are analysed and will be discussed.
Abstract G12 (Poster)
A future prediction of the ozone layer using the CCSR/NIES Chemistry-Climate
Model in the CCMVal-REF2 scenario
Hideharu Akiyoshi, Kei Sakamoto, Tatsuya Nagashima, Masaaki Takahashi, and Takashi Imamura
Global
ozone variation in the REF2 scenario of CCMVal was
calculated by the Center for Climate System Research, University of Tokyo /
National Institute for Environmental Studies (CCSR/NIES) chemistry-climate
model (CCM) in the years 1980-2100 using the Ab
scenario (WMO 2003, Table 4B-2) for the halogen concentration and the IPCC A1B
scenario (IPCC, 2000) for the greenhouse gas concentration. Table 1-16 in WMO
2003 is used for the halogen concentration after 2050. The sea-surface
temperatures for the past and future are prescribed by the outputs of an
atmosphere-ocean coupled general circulation model (CGCM) calculation for
climate change, which uses the same greenhouse gas scenario. The CGCM was
developed by CCSR, NIES, and the
The
results of the REF2 run suggest that the ozone hole will disappear around
2050-2065. A sensitivity run was performed, in which the concentration of the
global warming gases was fixed to the values at 1975 and the sea surface
temperature was fixed to the 1970s mean. Although this calculation was stopped
at the year 2063 by a computer renewal of NIES in March, the results suggest
that the global warming effect accelerates the disappearance of the ozone hole
by 10-20 years owing to ozone production in the colder stratosphere of the
future atmosphere. However, in order to make the conclusion we have to
carefully consider the low bias of stratospheric water vapor amount in the
current version of the CCSR/NIES CCM. A tropopause
height elevation in the future atmosphere of the REF2 scenario is obtained and
its effects on the ozone profile are analyzed and discussed. A small ozone hole
in a given year in high planetary wave activity with high equivalent effective
stratospheric chlorine EESC concentration in the REF2 run is also analyzed,
discussed, and compared with the observed 2002 ozone hole.
Abstract G13 (Poster)
Some results of time-dependent and time-slice simulations of
stratospheric chemistry, dynamics, and temperature from the GEOS CCM
Richard Stolarski, Steven Pawson, Anne Douglass, Paul Newman,
Randy Kawa, Qiung Liang, Eric Nielsen, Darryn
Waugh, and Luke Oman
This
paper will examine the co-evolution of ozone and temperature, particularly in
the upper stratosphere, in the simulations of the GEOS CCM. We demonstrate
that, in our simulations, nearly 2/3 of the temperature change in the northern
mid-latitude upper and lower stratosphere were
response to the changes in ozone over that time period. The temperature changes in both regions are
expected to be significantly smaller over the next two decades as the ozone
term changes sign with the projected beginning of ozone recovery. These temperature responses to ozone change
go in the same direction as the ozone change, i.e. ozone decrease implies
temperature decrease. As CFCs are removed
from the atmosphere, the temperature change due to increasing greenhouse gases
begins to dominate and the ozone response goes in the opposite direction as the
temperature change, i.e. temperature decrease implies ozone increase due to
temperature dependent ozone loss rates.
The result is a super-recovery of ozone over much of the upper
stratosphere. We will compare both ozone
and temperature changes from our past simulations with the data record and will
discuss the implication of these comparisons for the uncertainty in projection
into the future using CCMs.
Abstract G14 (Poster)
The impact of increasing methane concentration on stratospheric
chemistry and dynamics
Patricia Kenzelmann, Stephan Fueglistaler, Martin
Schraner, Eugene Rozanov, and Thomas Peter
Methane
is, after carbon dioxide, the strongest anthropogenic emitted greenhouse gas,
which results in warming the troposphere and cooling the stratosphere. Its
atmospheric concentrations roughly doubled in the last 100 years. Besides the
direct effect of methane as greenhouse gas, tropospheric
methane emissions influence the stratosphere chemically radiatively, and thus
dynamically.
Increasing
methane concentrations lead to higher water vapour
concentrations in the stratosphere. It is expected that this results in
enhanced ozone destruction by HOx-catalysed
destruction cycles. The distribution of chemical species in the stratosphere is
crucial for stratospheric temperatures, and the resulting perturbation of
stratospheric dynamics can propagate downwards into the troposphere.
By means
of the chemistry climate model SOCOL we performed sensitivity tests to
investigate the impact of methane increase on processes in the stratosphere and
troposphere. Steady state runs for pre-industrial 0.7 ppmV,
present 1.7 ppmV and possible future methane
concentration 2.7 ppmV suggest the following:
While
the water vapour content increases roughly linearly
with increasing methane, the perturbation in ozone differs in latitude and
altitude. Increasing methane concentrations reduce polar ozone destruction,
because active chlorine is reduced by reaction with methane. Conversely, ozone
decreases in the upper stratosphere and mesosphere, because of enhanced HOx chemistry. We will further discuss the asymmetric behaviour of the southern and northern hemisphere with
respect to changes in dynamics and chemistry related to methane concentrations.
Abstract G15 (Poster)
Stratospheric chemistry/climate simulations with the GEOS CCM
Eric Nielsen and Steven Pawson
This
work discusses the Goddard Earth Observing System Chemistry Climate Models (GEOS
CCMs.) The first version is based on the GEOS-4
General Circulation Model GCM coupled to a comprehensive stratospheric
chemistry component. A number of multi-decadal simulations spanning the period
1950-2100 are complete, and the results are being used to study problems
associated with ozone and climate in the current and future stratosphere. Some
of the results will be presented, while others are included in the CCMVal model inter-comparison evaluations. A second version
of GEOS CCM is recently complete, and it utilizes the chemistry component of
the first version integrated into the next generation GEOS-5 GCM. A few
sensitivity experiments have been run, and the impacts of gravity wave drag on
polar stratosphere dynamics and ozone are discussed. Development is now focused
upon integrating a combined troposphere-stratosphere chemistry module into
GEOS-5. Our strategy for future simulations will be illustrated. Some early results
may be shown.
H. Effect of Stratosphere on
Troposphere
Abstract H1 (Oral)
Volcano-induced Climate Impacts and ENSO Interaction
Georgiy Stenchikov and Thomas Delworth
Strong
explosive volcanic eruptions can produce global stratospheric aerosol clouds
affecting the Earth’s radiative balance. The climate responses to such volcanic
eruptions form as a result of the interaction of associated thermal and dynamic
perturbations of the major modes of climate variability, e.g., Arctic
Oscillation (AO) and El Nino-Southern Oscillation (ENSO). The paleo-proxy data (Adams et al., 2003) even suggest that
strong tropical eruptions could increase the likelihood of El Nino. It was also observed that the strong
low-latitude eruptions affect the mid-to-high-latitude circulation forcing an
anomalously positive phase of AO but the AO responses to volcanic forcing might
depend on the ENSO phase (Stenchikov et al., 2006).
The
strongest explosive eruptions of the second half of 20th century Agung, El Chichon, and Pinatubo
occurred in El Nino years and had a significant effect on the climate (Delworth et al., 2005; Ramaswamy
et al., 2006). The El Nino that occurred in the same year as the El Chichon eruption 1982 was especially strong and
significantly affected the climate response.
To better quantify an ENSO-Volcano-AO interaction in this study we
employed a coupled climate model (GFDL CM2.1) and specifically designed the
numerical experiments to study how volcanic eruptions could perturb AO and ENSO
and how the ENSO phase could affect the AO sensitivity and global climate
response. As a test eruption we have
chosen the strongest and best observed eruption in 20th century -- that of
We found
that in CM2.1 simulations volcanic forcing cannot affect the phase of
ENSO. However, the surface air
temperature anomaly depends significantly on ENSO. The maximum cooling for El Nino cases tends
to shift to the second year after the eruption.
In La Nina cases maximum cooling appears in the year when the eruption
occurred. However, the temperature
responses appear to be very similar in both El Nino and La Nina cases when the
SST effect was removed, suggesting a linear superposition of global responses
to volcanic forcing and SST. Because of
high climate variability in the coupled model we could not obtain a definite
conclusion about differences of the AO sensitivity to volcanic forcing for El
Nino and La Nina initial conditions.
Adams, B.
J., M. E. Mann, and C. M. Ammann, 2003 Proxy evidence
for an El Nino-like response to volcanic forcing, Nature, 426, 274-278.
Delworth, Thomas L., V. Ramaswamy, and Georgiy L. Stenchikov, 2005 The
impact of aerosols on simulated ocean temperature, heat content, and sea level
in the 20th century, Geophys. Res. Lett., 10.1029/2005GL024457.
Ramaswamy, V., M. D. Schwarzkopf, W. Randel,
B. Santer, B. J. Soden, G. Stenchikov, 2006 Anthropogenic and natural influences in
the evolution of lower stratospheric cooling, Science, 311,.1138-1141.
Stenchikov, G., K. Hamilton, R. J. Stouffer, A. Robock,
V. Ramaswamy, B. Santer,
and H.-F. Graf, 2006 Arctic Oscillation response to Volcanic
Eruptions in the IPCC AR4 Climate Models, J.
Geophys. Res., 111, D07107, doi:10.1029/2005JD006286.
Abstract H2 (Poster)
The influence of major volcanic eruptions on the atmosphere as
represented in different ECHAM model versions
Kirstin Krüger,
Janine Flöter, Ralf Hand, Claudia Timmreck,
Irene Fischer-Bruns, Marco Giorgetta,
Benedikt Steil, Christoph Brühl and Erich Roeckner
Since
the volcanic eruption of
One
version is the coupled atmosphere ocean model ECHAM5-OM1 with a top layer of
the model lid at 10 hPa (~30 km altitude). This model
was run in an IPCC type of experiment from 1860 to 1999 including the major
volcanic eruptions. To derive a statistical analysis three ensemble runs have
been carried out. The other model version is the Middle Atmosphere ECHAM4
coupled with the interactive chemistry tool CHEM (MAECHAM4-CHEM) with a model
top at 0.01 hPa (~80km altitude). This set up was
once run from 1960 to 1999 and secondly from 1980 to 1999.
Both
models have their advantages and disadvantages. The first model takes care of
atmospheric feedbacks with an interactive ocean, taking care of the longer term
memory of the ocean for climate change scenarios but without a realistic
representation of the Brewer-Dobson Circulation (BDC). The latter model is
coupled to an interactive stratospheric chemistry tool taking chemical
feedbacks of e.g. volcanic aerosols into account and the full branch of the
BDC.
The
influence of major volcanic eruptions (Mt. Agung
1963, El Chichon 1982 and Mt. Pinatubo 1991) on the
atmosphere will be analysed in both model setups analysing global temperature
anomalies, changes of the residual circulation and the Arctic oscillation
patterns in detail. Agreements and deficiencies between the two different model
setups will be used to derive a better understanding of the underlying
important atmospheric processes.
Abstract H3 (Poster)
Troposphere/Stratosphere coupling and its effect on Tropospheric
Ozone.
Richard Damoah, David Stevenson, Wenshou Tian
and Martyn Chipperfield
Two
detailed chemistry schemes, one tropospheric and one
stratospheric, have been coupled within the Met Office Unified Model HadAM3.
Both schemes have been used independently within the UM for many studies and
using them simultaneously provides a computationally efficient full
stratosphere-troposphere model. The tropospheric
scheme is from the STOCHEM model chemistry calculated up to 50 hPa, which integrates 70 species including detailed
non-methane hydrocarbon chemistry. Many of the natural sources e.g. lightning NOx, biogenic isoprene are derived interactively from the
climate model. In the stratosphere, we use the scheme from the SLIMCAT CTM
chemistry calculated above 145 hPa which contains a
description of Ox, NOy, HOx,
Cly, Bry, source gases and
CH4 oxidation as well as heterogeneous chemistry on sulfate aerosols
and polar stratospheric clouds. Both schemes operate independently but common
fields e.g. O3, CH4, CO, HNO3, NOx and N2O5 are exchanged between
the schemes. Model fields O3, CH4, CO, HNO3, NOx and N2O5 are merged in the
overlap region of the UT/LS 145 hPa-75 hPa every 3
hours.
We have
compared the coupled output with observations and model results from an
uncoupled version. The coupling led to an increase in modelled
tropospheric O3 concentrations of up to
100 in the lower/middle troposphere, but
much larger increases occur in the southern hemisphere and the upper
troposphere. Compared with observations the coupled model shows an improvement
over the uncoupled version where STOCHEM used a fixed stratosphere, which tends
to underestimate tropospheric O3. The
impact of coupling is least in the tropics where changes are less than 10%. Tropospheric ozone budgets were also affected by coupling
as follows: stratospheric input rose sharply by 120% chemical production fell
by 10% chemical loss almost unchanged and dry deposition rose by 10%. Both the
ozone burden and the ozone lifetime were approximately unchanged at 285 Tg and 19 days, respectively.
Abstract H4 (Poster)
Troposphere/Stratosphere coupling and its effect on Tropospheric
Ozone.
Wenshou Tian,
Richard Damoah, David Stevenson and Martyn Chipperfield
Two
detailed chemistry schemes, one tropospheric and one
stratospheric, have been coupled within the Met Office Unified Model HadAM3
(see poster by Damoah et al). Here we use results
from 2 runs of the model to investigate the impact of stratospheric ozone
recovery on tropospheric chemistry.
I. Data
Abstract I1 (Oral)
The role of BADC in CCMVal: Possibilities and
limitations
Martin Juckes
The British Atmospheric Data Centre
exists to collect, archive, curate and distribute
atmospheric data in support of