Download How is the stratosphere-troposphere coupling af

Application for Funding of the Research Proposal
How is the stratosphere-troposphere coupling affected by climate change, and how strong is the
climate feedback?
SHARP-STC
Project 4 of the DFG Research Unit (DFG-Forschergruppe)
‘Stratospheric Change and its Role for Climate Prediction’ (SHARP)
(FOR 1095)
Submitted by
Ulrike Langematz, Ulrich Cubasch
Institut für Meteorologie, Freie Universität Berlin (FUB)
Martin Dameris
Deutsches Zentrum für Luft- und Raumfahrt e.V., Institut für Physik der Atmosphäre, Oberpfaffenhofen
(DLR)
Marco Giorgetta
Max-Planck-Institut für Meteorologie, Hamburg (MPI-M)
May 2008
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
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General Information (Allgemeine Angaben)
New proposal (Neuantrag) as part of the DFG Research Unit ‘Stratospheric Change and its Role for
Climate Prediction’ (SHARP) (FOR 1095)
1.1 Applicants (Antragsteller)
Principal Investigator:
PD Dr. Ulrike Langematz
Institut für Meteorologie
Freie Universität Berlin
Carl-Heinrich-Becker-Weg 6-10
12165 Berlin
Phone: +49-30-838-711 65
Fax:
+49-30-838 717 85
[email protected]
private:
Spießweg 66
13437 Berlin
Phone: +49-30-41190754
Co-Investigators:
Prof. Dr. Martin Dameris
Deutsches Zentrum für Luft- und Raumfahrt e.V.
Institut für Physik der Atmosphäre
Oberpfaffenhofen
Münchner Straße 20
82234 Weßling
Phone: +49-8153-28 1558
Fax:
+49-8153-28 1841
[email protected]
Prof. Dr. Ulrich Cubasch
Institut für Meteorologie
Freie Universität Berlin
Carl-Heinrich-Becker-Weg 6-10
12165 Berlin
Phone: +49-30-838-71217
Fax:
+49-30-83871160
[email protected]
private:
Franz-Krämer Straße 24
82229 Seefeld
Phone: +49-8152-914944
private:
Teltower Straße 22
14109 Berlin
Phone: +49-39-80497025
Partner (without funding):
Dr. Marco Giorgetta
Max-Planck-Institut für Meteorologie
Bundesstraße 53
20146 Hamburg
Phone: +49-40-41173 358
Fax:
+49-40-41173 298
[email protected]
private:
Lutterothstraße 51
20255 Hamburg
Phone: +49-40-8800374
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
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1.2 Topic (Thema)
How is the stratosphere-troposphere coupling affected by climate change, and how strong is the climate feedback? (SHARP−STC)
Welche Auswirkung hat die Klimaveränderung auf die Kopplung zwischen Stratosphäre und Troposphäre, und wie stark ist die Rückkopplung auf das Klima? (SHARP-STC)
1.3 Scientific Discipline and Field of Work (Fachgebiet und Arbeitsrichtung)
Atmospheric Physics and Chemistry; Middle Atmosphere Chemistry and Dynamics, Chemistry-Climate
Interaction, Remote Sensing, Chemistry-Climate-Modelling
1.4 Scheduled Total Duration (Voraussichtliche Gesamtdauer)
The scheduled total duration of the DFG Research Unit SHARP is 6 years.
1.5 Application Period (Antragszeitraum)
First proposal (Neuantrag)
The application period for this proposal is 3 years, starting from 01 January 2009.
1.6 Summary
The focus of this project is to determine the role of the interaction between the stratosphere and troposphere in a changing climate, in particular to assess the impact of a changing stratosphere on surface
climate and weather. Observations and model studies have shown that the troposphere and stratosphere influence each other on different time scales, but the mechanisms responsible are not well understood. The new questions that will be addressed in this project are if the importance of the coupling
between the stratosphere and the troposphere will change in a changing climate and what the consequences will be for surface climate and weather.
Updated observations will be analysed to assess the characteristics of the stratosphere-troposphere
coupling in detail. Transient simulations of the past and future with state-of-the-art chemistry-climate
models (CCMs) will be performed and analysed to study how well current models are able to reproduce the observed coupling, to understand the responsible mechanisms, and to predict its future evolution. Complementary sensitivity simulations will be performed with a spectrum of models of different
complexity to isolate the effects of changes in greenhouse gases, stratospheric ozone, water vapour
and sea surface temperatures on near-surface climate by vertical coupling processes. The joint analyses will allow us to assess the role of stratospheric change on tropospheric key climate indices, like
the North Atlantic-Oscillation (NAO), and weather in the past and in the future.
Zusammenfassung
Ziel des Projektes ist die Untersuchung der Rolle von Wechselwirkungen zwischen Stratosphäre und
Troposphäre in einem sich verändernden Klima, insbesondere der Auswirkungen von Änderungen in
der Stratosphäre auf das bodennahe Klima und Wetter. Beobachtungsdaten und Modellstudien zeigen, dass sich Troposphäre und Stratosphäre auf verschiedenen Zeitskalen gegenseitig beeinflussen,
jedoch ist noch nicht verstanden, welche Mechanismen dafür verantwortlich sind. Die neuen Fragen,
die dieses Projekt vor allem beschäftigen werden, lauten: Wird sich die Bedeutung der dynamischen
Kopplung zwischen Stratosphäre und Troposphäre in einem sich ändernden Klima verschieben, und
welche Auswirkungen wird eine solche Verschiebung auf das bodennahe Klima und Wetter haben?
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
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Neuere Bobachtungsdaten werden analysiert werden, um die Eigenschaften der vertikalen Kopplung
zwischen Stratosphäre und Troposphäre im Detail zu beschreiben. Transiente Modellsimulationen für
die Vergangenheit und Zukunft mit aktuellen Chemie-Klimamodellen werden durchgeführt und analysiert werden mit dem Ziel, die Modelle hinsichtlich der beobachteten vertikalen Kopplung zwischen
Stratosphäre und Troposphäre zu überprüfen, die verantwortlichen Mechanismen zu verstehen und
ihre zukünftige Entwicklung vorherzusagen. Ergänzende Sensitivitätssimulationen mit einem Spektrum von unterschiedlich komplexen Modellen werden durchgeführt werden, um die Auswirkungen von
Änderungen der Treibhausgaskonzentrationen, stratosphärischem Ozon, Wasserdampf und der Meeresoberflächentemperaturen über die vertikale Kopplung auf das bodennahe Klima zu isolieren. Insgesamt werden die Untersuchungen dazu beitragen, die Bedeutung von Veränderungen in der Stratosphäre für troposphärische Schlüsselklimaindikatoren, wie die Nordatlantische Oszillation (NAO), und
das Wetter in der Vergangenheit und Zukunft besser zu verstehen.
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State of the Art, Preliminary Work (Stand der Forschung, eigene
Vorarbeiten)
2.1 State of the Art (Stand der Forschung)
2.1.1 Observational evidence of stratosphere-troposphere coupling
The stratosphere and troposphere are coupled by radiative, dynamical and chemical processes.
Changes in the chemical composition of radiatively active gases in the stratosphere lead to significant
changes in stratospheric temperature (e.g., Ramaswamy et al., 2001, Shine et al., 2003) as well as a
set of radiative forcings (RF) on the troposphere-surface system.
In addition, the stratosphere in winter is largely influenced by upward propagating tropospheric dynamical disturbances (waves) that dissipate and decelerate the stratospheric polar night jet. Statistical
analyses showed a high correlation between stratospheric and tropospheric modes of variability (e.g.,
Baldwin et al., 1994; Perlwitz and Graf, 1995; Kodera et al., 1996; Kitoh et al., 1996). During northern
winter, a high correlation exists between the intensity of the stratospheric polar vortex and the North
Atlantic Oscillation (NAO) in the middle troposphere (e.g., Schnadt and Dameris, 2003) which is a key
climate index for weather and climate in Europe. A strong polar vortex in the stratosphere is associated with a positive phase of the NAO, corresponding to enhanced westerlies over the North Atlantic
and positive temperature anomalies over central and northern Eurasia, and vice versa. Thompson and
Wallace (1998) found vertically coherent patterns from the stratosphere down to the surface with more
zonally-symmetric, annular anomalies of opposite polarity at polar and mid latitudes. This variability
pattern is called Arctic Oscillation (AO) near the surface, respectively Northern Annular Mode (NAM) in
the atmosphere. A similar variability pattern exists in the southern hemisphere, the near-surface Antarctic Oscillation (AAO), respectively the Southern Annular Mode (SAM) at higher levels. While NAM
and SAM exist in the troposphere throughout the year, they extend into the stratosphere in winter and
spring when stratospheric dynamical variability is enhanced (Thompson and Wallace, 2000). During
northern winter, NAM anomalies associated with anomalously strong or weak polar vortices usually
appear in the upper stratosphere first, and propagate downward to the troposphere where they show
up as anomalies of tropospheric meteorological fields with a time lag of several weeks (Baldwin and
Dunkerton, 1999; Baldwin and Dunkerton, 2001). These studies indicate that the stratosphere does
not only play a passive role.
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Most previous observational studies of the vertical dynamical coupling between troposphere and
stratosphere were based on NCEP/NCAR reanalyses resolving only the lower to middle stratosphere
up to 10 hPa (30 km).
2.1.2 Stratosphere-troposphere coupling on sub-seasonal time-scale
Thompson et al. (2002) found a high correlation between extreme weather events and the strength of
the stratospheric polar vortices, hence implying that considering stratospheric anomalies in winter
might improve the seasonal weather forecast. Baldwin et al. (2003, 2007) emphasised the importance
of persistent circulation anomalies in the lower stratosphere in winter for the phase of the Arctic Oscillation. They concluded that this stratospheric memory effect could benefit the predictive skill for extended-range weather forecasting. Charlton et al. (2003) reported a statistical forecast model that incorporates the stratosphere, which however underestimates the coupling between the stratosphere
and troposphere. In a similar study of ERA-40 reanalyses, Christiansen (2005) found that the inclusion of information from the lower stratosphere improved the prediction of the near-surface zonal
mean wind at 60°N and the temperature in northern Europe. For lead times larger than 5 days, predictors in the stratosphere revealed better forecasts than predictors in the troposphere. But understanding of the physical mechanisms is missing.
2.1.3 Stratosphere-troposphere coupling on climate time-scale
On climate time scales, changes in tropospheric variability are associated with stratospheric variability
of either natural or anthropogenic origin. Kodera (2002) showed that during the maximum of the 11year solar cycle the initial radiative solar signal leads to changes of the stratospheric zonal mean wind
that in winter are highly correlated with the NAO index. A similar correlation between the stratosphere
and troposphere was found for the Southern Annular Mode (SAM), but only during solar maximum
conditions (Kuroda and Kodera, 2005). These observational results were confirmed by GCM studies:
Matthes et al. (2006) found significant differences in the near-surface northern hemisphere (NH) geopotential height between solar minimum and maximum resembling the signature of the AO, with more
positive phases during solar maximum. Stronger stratospheric polar vortices during solar maximum
are associated with stronger tropospheric cyclone activity over the North Atlantic and warm and humid
winters over central Europe and Eurasia.
Similarly, the near-surface temperature anomalies following large volcanic eruptions (the ‘continental
winter warming’) resembled anomalies associated with the positive phase of the NAO (e.g., Robock
and Mao, 1992; Kelly et al. 1996). GCM simulations (e.g., Kirchner et al. 1999; Shindell et al. 2001)
showed that dynamical feedback processes initiated by the tropical stratospheric warming due to sulphur aerosols were responsible for the tropospheric response (e.g., Kodera 1994; Walter and Graf,
2006).
In addition to the above described naturally forced components of stratosphere-troposphere coupling
anthropogenically induced contributions are important. The stratosphere is strongly sensitive to radiative perturbations, as caused by the observed decrease of stratospheric O3, and increases in wellmixed greenhouse gases (GHG) and water vapour (Rosier and Shine, 2000; Langematz et al., 2003;
Shine et al., 2003). In a transient climate model simulation Schwarzkopf and Ramaswamy (2008)
found a sustained and significant global, annual-mean cooling since ~1920 in the lower-to-middle
stratosphere (~20-30 km), a global temperature change signal developing earlier than in any lower
atmospheric region, that largely results from carbon dioxide increases. After 1979, stratospheric O3
decreases reinforce the cooling. Forster et al. (2007) used a radiative fixed dynamical heating model
to show that the effects of tropical ozone decreases at 70 hPa and lower pressures can lead to signifi-
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
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cant cooling not only at stratospheric levels, but also in the ‘‘sub-stratosphere/upper tropospheric’’ region around 150–70 hPa. These lower stratospheric O3 decreases have been shown to change the
radiative forcing of climate comparable in magnitude to other trace gases (e.g., Chapter 5 in WMO,
2007).
Thompson and Solomon (2002) found an increase of the tropospheric circumpolar circulation since
the 1970s with a warming of the Antarctic Peninsula and Patagonia and a cooling of East-Antarctica
and the Antarctic plateau, being associated with a shift to a more positive phase of the SAM. Similar
tropospheric signatures were obtained in GCM simulations with prescribed stratospheric polar ozone
losses. An induced cooling was shown to lead to more positive phases of the AO and AAO (Kindem
and Christiansen, 2001; Schnadt and Dameris, 2003; Gillett and Thompson, 2003). GCM simulations
of the influence of increasing greenhouse gas (GHG) concentrations revealed a positive trend in the
AO in the troposphere (Fyfe et al., 1999; Shindell et al, 1999; Gillett et al. (2002). However, these
studies came to contradictory conclusions on the relevance of the stratospheric contribution (cf. 2.1.5).
2.1.4 Mechanisms of stratosphere-troposphere coupling
The observed vertical dynamical coupling between stratosphere and troposphere (cf. 2.1.1) is broadly
reproduced in general circulation model (GCM) studies. In perpetual January simulations with a
stratosphere resolving GCM, Christiansen (2000) showed that a significant part of tropospheric variability is explained by anomalies propagating downward from the stratosphere. Idealised model experiments with prescribed disturbances of the stratospheric circulation, e.g., through the variations of
the mechanical damping or prescribed thermal anomalies, led to responses of the near-surface climate (Polvani and Kushner, 2002; Norton, 2003; Taguchi, 2003).
However, the mechanisms involved in the downward coupling between the stratosphere and the troposphere remain elusive. The proposed mechanisms include:
•
Planetary wave propagation: The vertical propagation of planetary waves from the troposphere to the stratosphere is influenced by the stratospheric polar vortex, and particularly sensitive to the vertical wind shear across the extratropical tropopause (Chen and Robinson,
1992) which varies with the annular modes (Limpasuvan and Hartmann, 1999). Perlwitz and
Harnik (2003) propose that wave reflection from the upper stratosphere influences the tropospheric circulation.
•
Planetary scale wave-mean flow interaction: The interaction between planetary waves and the
zonal mean flow in the stratosphere may lead to a downward propagation of zonal wind
anomalies that may reach the lower troposphere and surface (Kodera, 1994; Christiansen,
1999).
•
Direct responses to the rearrangement of potential vorticity: Hartley et al. (1998) and Black
(2002) found that changes in the zonal circulation in the lower stratosphere can lead to significant changes in the tropopause height and tropospheric winds.
•
Downward control (Haynes et al., 1991): In the case of sufficiently long anomalous wave driving secondary equilibrium circulations develop in the stratosphere, which extend to the troposphere.
These mechanisms are not independent of each other, but is not clear so far how they act together to
produce the observed stratosphere-troposphere coupling. Song and Robinson (2004) found in idealised General Circulation Model (GCM) studies with implied stratospheric torque robust tropospheric
signals which result from a tropospheric enhancement by transient eddies of the weak initial ‘downward control’ forcing from the stratosphere. But additional effects of stratospheric planetary waves
seem to be necessary to explain the observed tropospheric response. An additional mechanism that
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
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possibly resolves the discrepancies between the observed and simulated tropospheric signal is the
influence of stratospheric conditions on baroclinic instability in the troposphere (Wittman et al., 2004).
Synoptic-scale tropospheric responses to stratospheric changes were also found by Charlton et al.
(2004). Simulations with simplified GCMs indicate that changes in both planetary wave propagation
and planetary wave energy due to tropospheric climate change are important (Rind et al., 2005). So
far no CCM simulations have been analysed in this regard.
2.1.5 Relevance of the stratosphere
While Thompson and Solomon (2002) implied an active role of the stratosphere in the development of
extreme tropospheric weather events, Polvani and Waugh (2004) pointed out that the stratosphere
itself is forced by tropospheric dynamical anomalies, and rather acts passively or as a mediator transferring initial tropospheric anomalies back to the troposphere.
The impact of stratospheric variability seems to be covered qualitatively by stratosphere resolving
models (cf. 2.1.4). In contrast, Stenchikov et al. (2006) und Miller et al. (2006) concluded that the tropospheric climate response due to volcanic eruptions was underestimated by the IPCC AR4 oceanatmosphere GCMs, most of which do not resolve the stratosphere. Fyfe et al. (1999) and Gillett et al.
(2002) (cf. 2.1.4) argued that the effects of increasing GHGs can be simulated in GCMs without
stratospheric dynamics. In contrast, Shindell et al. (1999, 2001) emphasised the important role of the
stratosphere for simulating realistic tropospheric AO trends in their GCM. Scaife et al. (2005) showed
that the IPCC climate projections of the 20th century indeed revealed a positive trend in the NAO even in models without stratospheric resolution - however the magnitude of the observed NAO trend
was underestimated by the models. Including stratospheric dynamics strongly improved the simulated
magnitude of the observed NAO trend between 1960 and 1990. This result indicates that stratosphere-troposphere coupling may play a specific role for enhancing regional tropospheric climate patterns. It is consistent with Rind et al. (2005) who found a larger impact of a stratospheric forcing on the
NAO than on the AO. Whether the under-representation of the vertical coupling in the models is related to the missing stratospheric resolution remains to be solved.
The stratospheric response to climate change plays a potentially important role for tropospheric climate. The sign of the stratospheric response to tropospheric climate change will therefore be of major
interest. Current model projections however do not reveal a coherent picture of the stratospheric
change, ranging from a projected increase of the stratospheric polar vortex in a future climate (Shindell et al., 1999) to a projected decrease of the stratospheric polar vortex due to enhanced tropospheric wave forcing in a future climate (Schnadt et al., 2002; Huebener et al., 2007). Stratospheric O3
is believed to recover in the first half of the 21st century, leading to a weakening of the polar vortex,
while rising CO2 levels might counteract this process (Arblaster and Meehl, 2006).
2.2 Preliminary Work (Eigene Vorarbeiten)
2.2.1 FUB
FUB has investigated stratospheric dynamics, variability and changes, based on observational data
and numerical model studies, for nearly 50 years. The continuous assessment of sudden stratospheric
warmings (SSWs) since the late 1950s from our own stratospheric analyses (e.g., Labitzke et al.,
2002) provides an excellent basis for the validation of GCMs and CCMs. The properties and occurrence frequencies of SSWs form the stratospheric component of the NAM, and have been studied in
simulations with the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) and observations (Erlebach et al., 1996; Braesicke and Langematz, 2000).
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
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The impact of anthropogenic climate forcing on stratospheric variability and the coupling to the troposphere was studied. Langematz et al. (2003) investigated the radiative and dynamical responses of
the stratosphere to the observed stratospheric ozone depletion and increasing greenhouse gas concentrations (GHG) for the period 1980-2000. In simulations with FUB-CMAM increases of upward
propagating tropospheric eddy heat fluxes were diagnosed when GHGs were enhanced, which are
indicative of changes in the vertical coupling. This was in contrast to the radiative cooling due to the
ozone depletion (Shine et al., 2003) and associated with a net intensification of the stratospheric polar
vortices in both hemispheres and a delay of the polar vortex breakdown in spring. The role of ozone
depletion for dynamical changes is less clear in the northern hemisphere (NH) where dynamical variability is much higher. Langematz and Kunze (2006) showed that due to a number of dynamically very
active winters since 2000 a polar vortex intensification in NH winter and spring cannot be found.
Decadal variations in solar activity also affect tropospheric variability via downward coupling. Simulations with the FUB-CMAM (Matthes et al., 2004; 2006) and more recently with the ECHAM5/MESSy
model showed that during the maximum phase of the 11-year solar cycle the phase of the Arctic Oscillation (AO) in the lower troposphere is in a more positive phase than during the minimum activity
phase, resulting in stronger westerly winds and warmer winters over central Europe (Figure 1). A consistent response of tropospheric climate to a reduction in solar activity during the Maunder Minimum in
the 17th century with an enhanced number of winters in the negative AO phase, more blockings over
Europe and colder winters in Europe was found by Langematz et al. (2005). The simulated tropospheric responses to stratospheric forcings confirm the role of vertical coupling.
Figure 1: Changes of the NH 1000 hPa geopotential height (left, contour interval: dam) and temperature (right,
contour interval: 0.5 K) in January from minimum to maximum activity of the 11-year solar cycle. Simulations with
the ECHAM5/MESSy model. Shaded areas in the left figure indicate negative values, orange areas in the right
figure statistical significance at the 99% level. (Figure taken from Kubin et al., 2007.)
Recently FUB investigated the vertical dynamical coupling in a 100-year control simulation for present
day conditions (i.e. 1990) of the stratosphere resolving atmosphere-ocean climate model (AOGCM)
EGMAM (Huebener et al., 2007). The model reproduces the observed vertical coupling (Baldwin and
Dunkerton, 1999): In EGMAM, the Arctic Oscillation appears as a vertically coherent variability mode
propagating from the stratosphere to the troposphere during NH winter (Langematz et al., 20081) (Figure 2). Future climate projections performed with EGMAM for IPCC 4AR clearly show an increase of
dynamical activity in NH winter for the end of the 21st century with more intense major SSWs than to-
1
in preparation
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
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day (Huebener et al., 2007). The analysis of the effects of this enhanced stratospheric variability on
tropospheric climate and weather is in progress.
FUB will perform CCM simulations for SHARP-STC using of the ECHAM5-MESSy CCM. The model
has been installed on two different super-computers in Berlin by the FUB-group and is applied successfully for solar variability studies within the DFG SPP CAWSES project ProSECCO. The FUBgroup has contributed to the improvement of the shortwave radiation code of the model (Nissen et al.,
2007). Within the SCOUT-O3 project the FUB-group has coupled the CCM to the MPIOM ocean module thus creating one of the first middle atmosphere atmosphere-ocean chemistry-climate models. The
AO-CCM version will be ready for use in the second phase of SHARP.
Figure 2: Composites of the time-height evolution of the Arctic Oscillation for 73 ‘weak vortex events’ (left) and 204
‘strong vortex events’ (right panel) in the EGMAM simulation. The events are defined by the dates when the AO
index is lower (higher) than -3.0 (+1.5). The stratospheric AO signal reached the lower troposphere with a time lag
of about 3 weeks. (Figure taken from Sinigoj, 2007.)
2.2.2 DLR
In recent years DLR has applied the CCM E39C (Hein et al., 2001; Dameris et al., 2005) successfully
in a number of chemistry-climate studies, based on time-slice (e.g., Schnadt et al., 2002; Schnadt and
Dameris, 2003; Grewe et al., 2004; Stenke and Grewe, 2005) as well as transient simulations (e.g.,
Dameris et al., 2006; Dameris and Deckert, 2008; Deckert and Dameris, 2008). The simulation results
have been used in internationally organised inter-comparison activities (e.g., Austin et al., 2003; Eyring et al., 2006; 2007) and assessment reports (e.g., IPCC/TEAP, 2005; WMO, 2007). These and
other studies with E39C have demonstrated the potential of the model system for atmospheric research. Schnadt and Dameris (2003) is of particular importance with regard to SHARP-STC since it
shows the capabilities of E39C to investigate the stratosphere-troposphere coupling. It investigates the
relationship between North Atlantic Oscillation (NAO) changes and northern stratospheric ozone recovery in the near future using four time-slice simulations (1960, 1980, 1990, and 2015). A wintertime
NAO index composite study of the scenario ‘‘1990’’ and of the ECMWF reanalyses shows the typical
NAO patterns: in the positive phase of the NAO the stratospheric polar vortex is stronger and colder
than in the negative phase. In the troposphere, the positive phase of the NAO is marked by increased
variance across the North Atlantic storm track whereas the negative phase is suggestive of blocking.
Consistently, vertical stationary (transient) wave propagation is reduced (enhanced) in the positive
phase. The model NAO index decreases significantly from ‘‘1990’’ to ‘‘2015’’. This coincides with enhanced vertical stationary wave propagation and a dynamical heating of the northern polar stratosphere. Thus, tropospheric circulation changes might influence stratospheric dynamics and hence the
evolution of ozone in the northern hemisphere.
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DLR will apply the CCM E39C-A (Stenke et al., 2008), a model version clearly superior to the CCM
E39C. E39C-A uses the fully Lagrangian advection scheme ATTILA (Reithmeier and Sausen, 2002) to
transport water vapour, cloud water and chemical tracers, instead of the older semi-Lagrangian advection scheme (SLT). ATTILA is strictly mass conserving and numerically non-diffusive. Some of the major benefits of ATTILA in connection with E39 (i.e. model version without interactive chemistry) are
summarised in Stenke et al. (2007) and Reithmeier et al. (2008). For example, transport studies with
passive tracers have demonstrated that ATTILA is able to maintain steeper and more realistic gradients. Using ATTILA instead of SLT hence results in a steeper meridional water vapour gradient in the
sub-tropical regions. The water vapour mixing ratios in the extra-tropical lowermost stratosphere are
significantly lower (by up to 70%), which is in agreement with observations. The cold bias in the polar
lower stratosphere is reduced substantially by about 5-7 K, and the cold pole problem in the polar
middle stratosphere by approximately 2-5 K. Further positive effects comprise a much better reproduction of both, the extra-tropical tropopause and the annual cycle of climatological zonal mean wind
fields, including the transition from westerlies to easterlies in the Southern Hemisphere lower stratosphere (above about 40 hPa) during November to January (cp. Figure 11 in Stenke et al., 2007),
which was not adequately captured by E39C. This results in a more realistic representation of planetary wave activity (Figure 3) which in turn improves the dynamic variability of the model.
January
10
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16
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0
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Pressure (hPa)
30
m ]
0.25
EP div [10
Pressure (hPa)
10
2.5e19 m3Pa
30
100
July
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Figure 3: January and July climatologies of EP fluxes (black arrows) and their divergences (coloured) over 40
years (1960-1999) calculated from E39C-A. Divergences are given in units of m3 and fluxes in m3 (horizontal
component) and m3 Pa (vertical component) due to weighting by mass. The scale of the vertical flux is indicated
in the upper left corner of the upper panel, a horizontal arrow of same length represents a flux of 0.436*1016 m3.
(Figure taken from Stenke et al., 2008.)
E39C-A provides a reliable basis for process studies of changes in stratosphere-troposphere coupling.
E39C-A has a vertical resolution of 39 levels up to the top layer centred at 10 hPa with a spectral horizontal resolution of T30 (about 6° isotropic resolution). The corresponding Gaussian transform grid, on
which tracer transport, model physics, and chemistry are calculated, has a mesh size of approximately
3.75°x3.75°. The time step of integration is 24 minutes. A detailed description of the chemistry module
and relevant assumptions, parameterisations, boundary conditions, etc. is given in Dameris et al.
(2005). A new model version, based on ECHAM5/MESSy, is currently under development at DLR. It
has 41 height levels (L41) with an uppermost level centred at 5 hPa and a T42 (about 4.3° isotropic)
horizontal resolution. Following an intensive testing phase (which is not part of SHARP-STC) this
model version is a further option in SHARP-STC, probably during the second half of the project.
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
11
2.2.3 MPI-M
MPI-M has developed general circulation models (GCMs) for the atmosphere and the ocean for many
years as major tools for the investigation of the climate, its natural fluctuations as well as the anthropogenic changes (e.g., Giorgetta et al., 2006a). ECHAM5 (Roeckner et al., 2006) is the current atmospheric GCM, used for tropospheric studies as well as for studies including the middle atmosphere
(Manzini et al., 2006). This middle atmosphere version, known as MAECHAM5, allows the simulation
of the quasi-biennial oscillation (Giorgetta et al., 2006b), which is the dominant mode of internal variability of the tropical stratosphere. ECHAM5 is also the base of the HAMMONIA model (Schmidt et al.,
2006; Schmidt and Brasseur, 2006) that extends to the lower thermosphere and includes chemistry
and other additional processes. The ECHAM5 atmospheric GCM and the MPIOM ocean GCM are
embedded in the COSMOS Earth system model for coupled climate simulations.
Recent work at MPI-M has made use of the MAECHAM5/MPIOM coupled middle-atmosphere ocean
model to investigate the effect of stratospheric processes on tropospheric climate, in comparison to a
conventional ECHAM5/MPIOM climate simulation that was performed for IPCC AR4, in which the
stratosphere is represented crudely. Preliminary results show that the stratospheric differences cause
changes in the Brewer-Dobson and Hadley circulation, such that the tropospheric climate and the upper ocean conditions adjust over approximately 60 years to a climate that is about 0.5°C warmer
(Giorgetta et al., 2007; Manzini et al., Chapman conference, Santorini, 24-28 September 2007). The
simulations, both having the same resolution and using the same parameterisations in the troposphere, show that the tropospheric climate is sensitive to changes in the stratospheric representation.
It was also demonstrated that the tropospheric response to changes in the stratosphere is different in
atmosphere models with given lower boundary conditions and in coupled atmosphere ocean models.
3
Goals and Work Schedule (Ziele und Arbeitsprogramm)
3.1 Goals (Ziele)
SHARP-STC aims to improve the understanding of the coupling between the troposphere and the
stratosphere. The focus is on the importance of the stratosphere for future changes of tropospheric
climate and weather. The following questions will be studied:
1. What are the characteristics of the stratosphere-troposphere coupling in the past?
2. Which mechanisms are responsible for the stratosphere-troposphere dynamical coupling?
3. How is the stratosphere-troposphere coupling affected by different future climate change scenarios?
4. What are the consequences for tropospheric climate and weather?
5. What is the relevance of the stratosphere for tropospheric predictability?
Questions 1 to 5 will be addressed by analyses of observational datasets and numerical model simulations which either exist or will be performed within the projects SHARP-BDC and SHARP-STC. Different observational data sets will be analysed to update and extend former work, e.g., from Baldwin et
al. (1999). This will allow us to include the upper stratosphere (above 10 hPa, 30 km) into the analysis,
as well as to consider the recent winters since 2000 which were characterised by enhanced dynamical
variability in the stratosphere. This task will provide the data base for the evaluation of the dynamical
vertical coupling in the models.
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
12
Most contributing models are based on the ECHAM general circulation model, developed at the MaxPlanck-Institut für Meteorologie, and use the same dynamical core. However, the models differ in their
complexity in terms of physical parameterisations, tracer transport, horizontal and vertical resolution,
model top, and degree of coupling. This will allow the interpretation of differences between the model
results by for example missing processes or resolution in one of the realisations. An overview of the
models is given in Table 1.
The core models of SHARP-STC are two state-of-the-art Chemistry-Climate-Models (CCMs), E39C-A
and ECHAM5/MESSy. CCMs are the most complete models as they include interactive chemistry
modules, hence take radiative, dynamical and chemical feedback processes into account. Only with
CCMs dynamical feedbacks of chemically driven composition changes can be assessed. The two
CCMs will be used to investigate how well the current generation of CCMs is able to reproduce the
observed vertical coupling between the stratosphere and troposphere during the past (cf. Question 1).
For this purpose existing multi-decadal transient simulations will be analysed. The CCMVal defined
reference simulation REF1 of the past (1960-2005) is going to be performed during 2008 as contribution to the next WMO/UNEP ozone assessment report. The simulation includes identical, observational estimates of climate change forcings of the past (GHGs, CFCs, volcanic aerosols, solar irradiance, sea surface temperatures and sea ice). The experimental setup of the simulations follows the
recommendations by the SPARC CCMVal2 group for new worldwide CCM simulations agreed upon
during the CCMVal Workshop in June 2007. Further details of the experimental setup for the planned
REF simulations are given in the SPARC-newsletter (30) and on the CCMVal website
(http://www.pa.op.dlr.de/CCMVal/ SPARC_CCMValReport/SPARC_CCMValReport.html).
Short description
Name of Model
Horizontal
resolution
Ver. resolution
/top height
Specifics
References
E39C-A
CCM based on
ECHAM4/CHEM
T30
(3.8°x3.8°)
L39 / 10 hPa
low top; high vertical
resolution in UTLS;
Lagrangian advection
scheme (ATTILA);
interactive chemistry
Dameris et al., 2005
Stenke et al., 2007
Stenke et al., 2008
Reithmeier and
Sausen, 2002
ECHAM5/MESSy
(also E5/M)
CCM based on
ECHAM5 with
MECCA chemistry
T42
(2.8°x2.8°)
L39 / 0.01 hPa
L90 / 0.01 hPa
high top; interactive
chemistry
Jöckel et al., 2005
Jöckel et al., 2006
Nissen et al., 2007
ECHAM5
GCM
T63
(1.9°x1.9°)
L31 / 10 hPa
low top
Roeckner et al., 2006
T63
(1.9°x1.9°)
L47 / 0.01 hPa
high top; tropospheric
resolution as in L31
Manzini et al., 2006
T63
(1.9°x1.9°)
L95 / 0.01 hPa
high top; high vertical
Giorgetta et al., 2006
resolution; in-situ QBO
T63
(1.9°x1.9°)
L31 / 10 hPa
GCM with interactive
ocean
Jungclaus et al., 2006
T63
(1.9°x1.9°)
L47 / 0.01 hPa
high top GCM with
interactive ocean
Giorgetta et al., 2007
ECHAM5/MPIOM
AOGCM
(Climate model)
EGMAM
AOGCM
(Climate model)
T30
(3.8°x3.8°)
L39 / 0.01 hPa
high top GCM with
interactive ocean
Huebener et al., 2007
SGCM
Simplified GCM
T42-T85
L40 / 0.007 hPa
dry dynamical core
with simplified physics
Gerber and Polvani,
2008
Table 1: Numerical models contributing to SHARP-STC
2
CCMVal (Chemistry-Climate Model Validation) is an activity of the World Climate Research Programme – Stratospheric Processes and their Role in Climate (WCRP-SPARC).
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
13
By comparing the features of single episodes of stratosphere-troposphere coupling in the models with
each other and with observations it will be possible to explore and better understand the underlying
mechanisms (cf. Question 2). The interpretation will be supported by sensitivity simulations with a
simplified GCM (SGCM).
The major topic of this project, the impact of climate change on stratosphere-troposphere coupling will
be addressed by analysing future climate projections of the two CCMs E39C-A and ECHAM5/MESSy,
as well as existing IPCC simulations of the AOGCM EGMAM and additional sensitivity simulations
(SEN) to be performed in SHARP-STC and SHARP-BDC (cf. Questions 3 and 4).
Finally, the same model simulations will be investigated with special focus on the role of the stratosphere for tropospheric climate and weather (cf. Question 5). The interpretation will be supported by
simulations performed with the ECHAM5 and ECHAM5/MPIOM model series with varying horizontal/vertical resolutions and vertical extensions. The results of this task will contribute to the discussion
of the need to include a representation of stratospheric processes in global climate models used for
future IPCC assessment activities.
3.2 Work Schedule (Arbeitsprogramm)
3.2.1
Proposed Work
The work plan of SHARP-STC (Project 4) is composed of five main activities:
A 4.1: Stratosphere-troposphere coupling in the past
A 4.2: Mechanisms of stratosphere-troposphere dynamical coupling
A 4.3: Future projections of stratosphere-troposphere coupling
A 4.4: Stratosphere-troposphere coupling in different climate scenarios
A 4.5: Relevance of the stratosphere for predictability.
A 4.1: Stratosphere-troposphere coupling in the past
In A 4.1 the characteristics of the stratosphere-troposphere coupling in the past will be studied by using updated observational data sets and the best available model simulations with state-of-the-art
CCMs.
Most previous observational studies of the vertical dynamical coupling between troposphere and
stratosphere were based on NCEP/NCAR reanalyses or FUB stratospheric analyses resolving only
the lower to middle stratosphere up to 10 hPa (30 km). In order to study the contribution and relevance
of the upper stratosphere/lower mesosphere for the vertical coupling, SHARP-STC will use vertically
extended observational data sets (ERA-40 reanalyses, ECMWF interim analyses and operational
data). Updated time series will be analysed thus including the most recent dynamically variable winter
seasons in both hemispheres. In addition, NCEP/NCAR reanalyses will be used as complementary
data set to enhance the data base in the overlapping altitude regions and to constrain the results from
the ERA analyses. By comparing different observational data sets we expect to achieve more robust
signals. Using long-term time-series (since 1958) with daily (up to 6-hourly) temporal resolution will
allow the assessment of the downward propagation on sub-seasonal time scales, as well as of longterm changes during the past five decades. (WP 4.1.1)
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
14
Key parameters for stratospheric variability (e.g., planetary wave activity, zonal wind, frequency and
intensity of major stratospheric warmings, wave-mean flow interaction by Eliassen-Palm flux diagnostics) and tropospheric variability (e.g., storm track characteristics, variability patterns, North-Atlantic
Oscillation) will be derived. Vertical coherent modes of variability, like the Arctic and Antarctic oscillations (AO, AAO) or the Northern and Southern Annular Modes (NAM, SAM) and their vertical propagation, will be analysed.
In a second step we will investigate how well state-of-the-art CCMs are able to reproduce the observed stratosphere-troposphere coupling (WP 4.1.2). We will evaluate the CCMs by producing the
same analyses for the model data as for the observations. We will analyse model data from existing
multi-decadal transient REF1 simulations of the past (1960-2005) performed within the CCMVal initiative (see above). The REF1 simulations will provide the basis for the analyses in SHARP-STC and
SHARP-BDC.
Within
the
SHARP-consortium
results
from
the
two
CCMs
E39C-A
and
ECHAM5/MESSy will be available for the analysis. The models are complementary to each other in
terms of vertical resolution and vertical model domain: E39C-A extends to the middle stratosphere (10
hPa) with superior transport characteristics in the upper troposphere/lower stratosphere (UTLS), while
ECHAM5/MESSy resolves the stratosphere and mesosphere (upper lid at ~ 0.01 hPa, 80 km), but with
lower vertical resolution in the UTLS. In addition, results from CCM simulations of external SHARP
partners (e.g., the UMETRAC and SOCOL CCMs run at NIWA (New Zealand), the UKCA CCM run at
the University of Cambridge (United Kingdom); for more details see Project 5, SHARP-MAN) will be
used to enlarge the model ensemble and enhance the reliability of the statements. As the different
CCMs are forced with identical boundary conditions, uncertainties due to prescribed external forcings
are eliminated and reduced to differences in the model formulations.
The analyses will concentrate on the nature of the coupling between the stratosphere and troposphere
and its impact on surface climate and weather. This includes for example the propagation characteristics of planetary waves in the stratosphere and the feedback on tropospheric variability modes, like
NAO, AO, AAO, NAM, SAM. (WP 4.1.2)
The analyses will address for example the following questions:
•
Do the CCM simulations reproduce the observed decadal changes of the NAO, e.g., the positive
trend since the 1960s? How well is the observed trend reproduced, compared to the IPCC model
realisations? Does the impact of chemistry-climate feedback in the CCMs improve the reproduction of the observed trends?
•
Do the CCMs reproduce the observed and in idealised GCMs simulated connection between
stratospheric ozone depletion and the change in Antarctic surface climate?
A 4.2: Mechanisms of stratosphere-troposphere dynamical coupling
Episodes in the different models simulations, for example a winter with a highly disturbed stratospheric
polar vortex and a concurrent negative AO phase in the troposphere, will be analysed in detail and
compared with similar observed episodes to understand the mechanisms responsible for the vertical
coupling (WP 4.2.1, WP 4.2.2).
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
15
Specific questions to be addressed are:
•
What are the relative roles of zonally symmetric stratospheric anomalies versus planetary
waves for the tropospheric signal?
•
Do tropospheric dynamical processes enhance the initial stratospheric disturbance? What is
the role of synoptic scale, baroclinic eddies?
•
Do stratospheric disturbances ‘only’ trigger the intrinsic annular variability mode in the troposphere?
•
Do different processes act together?
With the pool of CCM, GCM and AOGCM simulations from the different SHARP projects, we will have
a unique data base to address the above questions in a more sound way than the previous studies
with simplified model systems. Targeted case studies with the SGCM will be performed by the external partner Columbia University, New York, in order to support the interpretation of the CCM results.
A 4.3: Future projections of stratosphere-troposphere coupling
The aim of A 4.3 is to figure out if and how the stratosphere-troposphere coupling will be affected in a
changing climate. We will assess possible changes of tropospheric climate, e.g., changes of the NAO
and European winter weather that may occur as a result of radiative and dynamical changes in the
stratosphere. To this end, we will analyse the best available future climate projections from CCMs, i.e.
the transient REF2 simulations of the future (1960-2050) performed within the CCMVal initiative (WP
4.3.1). The REF simulations are going to be completed by the end of 2008 as contribution to the next
WMO/UNEP ozone assessment report. They will include identical estimates of climate change forcings in the future (GHG increases, CFC decreases) according to the recommendations by the SPARC
CCMVal group. In addition, the CCMVal SCN2d simulation will be performed to take into account the
effect of natural climate forcing factors, i.e. volcanic aerosols and solar irradiance variations, on the
vertical coupling (WP 4.3.2). Within the SHARP-consortium results from the two CCMs E39C-A and
ECHAM5/MESSy will be available for the analysis. Like in A 4.1, CCM results from the external
SHARP partners will be provided to improve the statistics.
A 4.4: Stratosphere-troposphere coupling in different climate scenarios
The goal of A 4.4 is to understand and interpret the changes of tropospheric climate due to changes
in the stratosphere. To this end, we will analyse additional sensitivity simulations (SEN) to be performed in this project as well as in Project 1 (SHARP-BDC) to separate the role of single climate
change forcings for stratosphere-troposphere coupling and tropospheric climate and weather in the
future.
Emphasis will be put on the relative roles of radiative and dynamical responses to the prescribed forcings. For this purpose a tool will be used in E39C-A and ECHAM5-MESSy that allows the calculation
of the radiative forcing for given composition changes online during a simulation (Stuber et al., 2001),
thereby taking the stratospheric temperature adjustment, which indicates the temperature response
under the constraint of fixed dynamical heating rates (FDH approximation, Fels et al., 1980) into account. The FDH allows us to separate the direct radiative impact on the temperature field from the effect of the feedbacks. The tool has, e.g., successfully been applied in Stenke et al. (2007) to explain
the radiative origin of a cold model bias in the extratropical lower stratosphere.
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
16
The SEN simulations will consist of a series of time-slice (~20 years) model runs for specified years to
be performed with the different model types listed in Table 1. As time-slice simulations for a specific
date are less computationally demanding they allow one to include parameter variations. Thus in contrast to the transient REF simulations that contain the combined effects of climate change forcings, the
SEN simulations will allow us to study the response of the stratosphere-troposphere coupling to specific factors. In addition the statistical significance of climate change signals can be derived to support
the interpretation of the single transient simulations.
The SEN simulations to be analysed in SHARP-STC have been designed jointly with SHARP-BDC.
The set-up of 6 SEN experiments has been defined (SEN0-SEN5) of which SEN0 to SEN3 will be performed within SHARP-BDC, and SEN4 to SEN5 will be performed within this project (SHARP-STC).
While SHARP-BDC will focus on the investigation of the effect of climate change on the BrewerDobson Circulation (BDC), SHARP-STC will use the same experiments SEN0-SEN3 to examine the
effect of climate change on stratosphere-troposphere coupling (WP 4.4.1, WP 4.4.3).
Main features and motivation of the SEN0-SEN3 simulations in SHARP-BDC are (for more details cf.
SHARP-BDC):
•
SEN0: time-slice simulations for year 1850, stratosphere-troposphere coupling for preindustrial conditions and no climate change
•
SEN1: time-slice simulations for years 2000 and 2050; with prescribed (i.e. offline) chemistry
•
SEN2: role of Arctic sea ice – repetition of 2050 time-slice experiment (SEN1), but without
sea-ice covering of the Arctic region in summer (CCMs only)
•
SEN3: role of tropical and extra-tropical SST anomalies – repetition of the 2000 and 2050
time-slice experiments (SEN1) (CCMs only).
In addition, SHARP-STC will provide 2 SEN simulations that complement the SEN1-SEN3 series by
considering the feedback between stratospheric ozone decrease and increasing greenhouse gases
(SEN4) and the impact of possible changes in stratospheric water vapour, of which the sign is currently unclear (SEN5):
•
SEN4: role of stratospheric ozone in future – repetition of SEN1 simulations 2000 with fixed
ozone of ‘1960’ and 2050 with fixed ozone of ‘2000’. Related to Project 2 (SHARP-OCF). (WP
4.4.2)
•
SEN5: role of stratospheric water vapour in future – repetition of SEN1 2050 time-slice experiment with artificially reduced (0.5 x H2O) and increased (2 x H2O) stratospheric water vapour concentrations. Related to Project 3 (SHARP-WV). (WP 4.4.2)
A 4.5: Relevance of the stratosphere for predictability
The aim of A 4.5 is to identify the relevance of the stratosphere for tropospheric climate and weather
prediction. Most models used for climate predictions of the 4th IPCC assessment report are conventional atmospheric general circulation models (GCM) which at their lower boundaries have been coupled to ocean models to account for the interaction between the oceans and the atmosphere on multiannual time scales. Future changes of atmospheric composition are considered by prescribing scenarios of GHGs, while stratospheric O3 is either kept constant at present-day values or prescribed from a
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
17
transient 2d-model calculation. Moreover, these models resolve only the lower to middle stratosphere,
with their upper lid usually located at 10 hPa (~ 30 km).
The open question to answer in A 4.5 is which complexity of a model is required to achieve the most
realistic reproduction of the real atmosphere. Or, which error-bar, respectively uncertainty is associated with climate predictions from specific model types? The different model versions participating in
SHARP are ideally suited for this test. Comparing the results of GCMs (ECHAM5, MAECHAM5, EGMAM) with those of the CCMs (E39C-A and ECHAM5/MESSy) allow first investigations about the impact of interactive chemistry, particularly the importance of stratospheric ozone chemistry. The role of
prescribed and interactive sea surface temperatures (SSTs) can be studied by comparing the
ECHAM5 and EGMAM versions with and without coupled MPIOM as well as the CCM SEN3 runs.
Moreover, the role of resolving the upper stratosphere and lower mesosphere for representing the observed vertical coupling between stratosphere and troposphere can be studies by comparing the results from the low top and high top models (cf. Table 1).
The focus of the analysis will be the representation of the vertical stratosphere-troposphere coupling
and the tropospheric response in the different model versions. Specific questions to be addressed are:
•
Is the observed tropospheric signal, for example the observed positive trend in the NAO, well
enough reproduced in a low top model without interactive chemistry?
•
Does the inclusion of interactive chemistry improve the simulated tropospheric signal in a low
top model?
•
Is the representation of the full stratosphere needed to represent the tropospheric signal?
•
How important is the coupling with the ocean?
The analysis will concentrate on the major modes of variability and possible trends in the troposphere
as well as on the time scale of seasonal weather prediction. (WP 4.5.1)
3.2.2 Timeline and Milestones
The following Gantt-chart gives an overview of the main activities, work packages and milestones of
SHARP-STC. The delivery dates of model data to the other SHARP projects have been coordinated
with the individual working plans of these projects.
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
18
Summary of work-plan:
A 4.1:
WP 4.1.1:
WP 4.1.2:
Stratosphere-troposphere coupling in the past (m1-m18)
Analyses of stratosphere-troposphere coupling in updated long-term observations (interannual and decadal variability; long-term changes) (m1-m8)
Analyses of stratosphere-troposphere coupling in transient CCM and AOGCM simulations (inter-annual and decadal variability; long-term changes) (m1-m18)
A 4.2:
WP 4.2.1:
WP 4.2.2:
Mechanisms of stratosphere-troposphere dynamical coupling (m18-m36)
Process-oriented investigation of mechanisms of STC in observations (m18-m36)
Process-oriented investigation of mechanisms of STC in CCM simulations (m18-m36)
A 4.3:
WP 4.3.1:
Future projections of stratosphere-troposphere coupling (m1-m24)
Analysis of ST coupling and consequences for tropospheric climate and weather in future CCM and AOGCM simulations (m1-m24)
Performance of CCMVal SCN2d simulation with ECHAM5/MESSy (m1-m12)
WP 4.3.2:
A 4.4:
WP 4.4.1:
WP 4.4.2:
WP 4.4.3:
A 4.5:
WP 4.5.1:
Stratosphere-troposphere coupling in different climate scenarios (m9-m31)
Performance and analysis of no-climate change simulation SEN0 (m9-m20)
Performance and analysis of SEN4 (ozone change) and SEN5 (water vapour change)
simulations (m13-m28)
Analysis of SEN1 (greenhouse gas change), SEN2 (sea-ice change) and SEN3 (SSTchange) simulations (m19-m31)
Relevance of the stratosphere for predictability (m21-m36)
Investigation of effect of model configuration (low top/high top; GCM/CCM/AOGCM)
on ST coupling and consequences for tropospheric climate and weather forecast in all
model simulations (m21-m36)
Milestones:
M 1, M2:
M 3:
M 4:
M 5:
Delivery of data from future projections to other projects (m2, m12)
Mid-term report (m18)
Delivery of SEN0, SEN4 and SEN5 data to other projects (m18)
Final reporting; peer-reviewed papers ready for submission (m36)
Figure 4: Gantt-chart of SHARP-STC.
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
3.2.3
19
Partners and their main tasks
FUB
FUB will analyse the stratosphere-troposphere coupling in updated observational data sets (WP
4.1.1), as well as in the existing multi-decadal transient CCM simulations of the past (REF1) performed with the ECHAM5/MESSy and E39C-A CCMs, and in existing simulations of the AOGCM EGMAM performed for the 4th IPCC AR (WP 4.1.2). In addition, FUB will analyse the stratospheretroposphere coupling in the multi-decadal CCM simulations of the future (REF2) (WP 4.3.1) and perform the additional transient SCN2d simulation of the future (WP 4.3.2). FUB will study the mechanisms of stratosphere-troposphere coupling in the CCM results and the simplified GCM data together
with the external partners (WP 4.2.1, WP 4.2.2). Jointly with DLR, FUB will define, implement, and
analyse the supplementary time-slice sensitivity simulations SEN4 and SEN5 (WP 4.4.2), and analyse
the stratosphere-troposphere coupling in the sensitivity simulations SEN0-SEN3 provided by Project 1
(SHARP-BDC) (WP 4.4.1, WP 4.4.3). FUB will further study the relevance of the stratosphere by comparing the characteristics of stratosphere-troposphere coupling in the different model versions (WP
4.5.1). The simulations at FUB will be performed with the ECHAM5/MESSy CCM (Jöckel et al., 2006).
The dynamical core model ECHAM5 has been developed at MPI-M. The extended modular CCMversion has been provided by MPI-C. The model will be maintained and run by FUB in close cooperation with MPI-C. In parallel, the new extended atmosphere-ocean AOCCM version (ECHAM5/MESSy
coupled with MPIOM) developed at FUB will undergo a series of test simulations. The final AOCCM is
expected to be applicable in SHARP-STC at the end of the first 3-year funding period.
FUB: 1 PostDoc, 1 Student Research Assistant
DLR
DLR (jointly with FUB) will define, conduct and perform the supplementary time-slice CCM simulations
SEN4-5 with the CCM E39C-A (WP 4.4.2). The results from these simulations together with those derived from multi-decadal transient simulations (REF1 and REF2) and long-term observations will be
investigated (WP 4.4.1, WP 4.4.3, WP 4.1.2, WP 4.3.1). The focus of DLR is on process-oriented
analyses with regard to the transport of air masses, in particular the exchange of air masses between
the troposphere and the stratosphere (WP 4.2.2). The role of the TTL- and ExTL-region will be studied
as well as possible changes in a future climate with enhanced greenhouse gas concentrations and
related effects. DLR will concentrate on studying tracer transport in the upper troposphere/lower
stratosphere (UTLS) applying a full Lagrangian advection scheme, which is an innovative approach in
connection with a CCM. Additional sensitivity simulations (see SHARP-BDC) will be used to assess
the effects of stratospheric circulation changes and the impact of long-term changes of stratospheric
ozone (SHARP-OCF) and water vapour (SHARP-WV) on troposphere-stratosphere connections (WP
4.4.3).
DLR: 1 PhD
Tasks of other SHARP partners without funding from this project
MPI-M will analyse the frequency and intensity of the major dynamical modes of variability that couple
the troposphere and stratosphere in models of different complexity (WP 4.4.1, WP 4.4.3). This work
will make use of the stationary SEN0 and SEN1 simulations performed in the SHARP-BDC project.
The models to be used differ in the vertical extent (ECHAM5 L31 vs. MAECHAM5 L47), the vertical
resolution (MAECHAM5 L47 vs. MAECHAM5 L95) and the use of prescribed lower boundary conditions for SST and ice ((MA)ECHAM5) or of a coupled ocean model ((MA)ECHAM5/MPIOM). MPI-M
will investigate the effect of the different model simplifications (low/high top, low/high resolution, pre-
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
20
scribed SST/coupled ocean) on the intraseasonal as well as interannual variability of the NAM and
SAM.
3.2.4
Outlook for Phase 2 of SHARP-STC (project years 4 to 6):
In Phase 2, we will further extend the REF CCM simulations to the end of the century (~2100) to address the longer-term impacts of climate change on the stratosphere and the resulting changes in radiative and dynamical coupling of the stratosphere and troposphere. A focus of Phase 2 will be the
chemical coupling of the troposphere-stratosphere system by transport of chemical tracers through the
tropical and extra-tropical tropopause, and potential changes in a changing climate. Further, the relevance of ocean-atmosphere interactions will become a central point in Phase 2. By applying an atmosphere-ocean chemistry-climate model (AOCCM) including chemical composition changes in the
troposphere-stratosphere system on the one hand and an ocean module responding to composition
and dynamical changes on the other hand assessment studies with climate models will reach a higher
skill.
3.3 Experiments Involving Humans or Human Materials (Untersuchungen am
Menschen oder an vom Menschen entnommenem Material)
None
3.4 Experiments with Animals (Tierversuche)
None
3.5 Experiments with Recombinant DNA (Gentechnologische Experimente)
None
4
Funds Requested (Beantrage Mittel)
4.1 Staff (Personalbedarf)
4.1.1 Freie Universität Berlin (FUB)
1 BAT IIa (1 postdoctoral scientist, 100%) for 36 months
1 Student Research Assistant (studentische Hilfskraft), 40 hours/month for 36months
4.1.2 Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)
0.5 TVöD 13 (1 PhD-student/Doktorand) for 36 months
4.2 Scientific Instrumentation (Wissenschaftliche Geräte)
None
4.3 Consumables (Verbrauchsmaterial)
None
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
21
4.4 Travel (Reisen)
4.4.1 FUB
International conferences
Attendance of one international conference in Europe per year, 1 person –
presentation of project results (three times (2009-2011) à 1.200 EUR)
Total 4.4.1 (FUB):
3.600 EUR
4.4.2 DLR
International conferences
Attendance of one international conference in Europe per year, 1 person –
presentation of project results (three times (2009-2011) à 1.200 EUR)
Total 4.4.2 (DLR):
3.600 EUR
4.5 Publication Expenses (Publikationskosten)
Publication expenses are applied for in the Management Project (Project 5).
4.6 Other Costs (Sonstige Kosten)
None
5
Prerequisites for Carrying out the Project (Voraussetzungen für
die Durchführung des Vorhabens)
5.1 Composition of the Team (Zusammensetzung der Arbeitsgruppe)
5.1.1 FUB
Ulrike Langematz, PD Dr., is Professor at the Institut für Meteorologie of Freie Universität Berlin and
head of the working group ‘Dynamics of the Middle Atmosphere’. Her scientific interests are in the
fields of radiation, dynamics, and chemistry of the middle atmosphere with focus on stratospheric
ozone, the interaction between stratospheric chemistry and climate change, and solar variability. She
was/is PI in different national and European projects on climate change modelling (HGF-ENVISAT,
EuroSPICE, SCOUT-O3), solar cycle modelling (BMBF-MESA, SOLICE and CAWSES-ProSECCO)
and planetary modelling (HGF-Allianz ‘Planetary Evolution’). U. Langematz is involved in the international climate modelling activity CCMVal. She has been lead and co-author of several international
assessments, recently co-author of Chapter 4 (Polar Ozone: Past and Present) of the WMO Scientific
Assessment of Ozone Depletion: 2006.
Ulrich Cubasch, Prof. Dr., is the dean of the Geoscience Faculty of Freie Universität Berlin and is
heading the climate variability section at the Institute für Meteorologie. His main areas of work are the
modelling of climate variability on timescales from decades to millennia and relating it to projections of
future climate change. The current emphasis of his research is the role of the stratosphere and solar
variations in climate variability. He has headed several EU-projects, coordinates a research theme in
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
22
the EU-project ENSEMBLES and is participating currently in various EU- and DFG-projects (DeSurvey, SOLVO, CAWSES-ProSECCO, RIFT-LINK, STAMPF). He is a lead author for IPCC WG1. He is
advisor for the EU-project QUANTIFY and review editor for the journal "Climatic Change".
Markus Kunze, Dipl. Met., scientist at FUB, is an expert in statistical and dynamical analyses of CCM
and observational data. He is familiar with all aspects of the implementation of the ECHAM5/MESSy
CCM at the Berlin super-computers, the data archiving and the post-processing.
Thomas Spangehl, Dr., Postdoc in the project ProSECCO of the DFG priority program CAWSES. He
studies the impact of centennial solar variability on climate and tropospheric variability in simulations
with the EGMAM model. He has expertise in the data analysis of the EGMAM model simulations.
5.1.2 DLR
Martin Dameris, Prof. Dr., is Senior Scientist at DLR-IPA and University Professor (Apl.) at the Meteorological Institute, Ludwig-Maximilians-Universität (LMU) in Munich, Germany. His scientific work is
focusing on modelling of chemistry-climate connections, employing a coupled model system of the
troposphere and the stratosphere. Main objectives are: the variability of the stratospheric ozone layer
and its future evolution; the influence of climate on atmospheric dynamics: investigation of cause and
effect relationships. He is author and co-author of more than 50 peer-reviewed scientific papers. He
was actively involved in several international assessment reports, for example he was Lead Author of
Chapter 5 (Climate-Ozone Connections) in the recent WMO Scientific Assessment of Ozone Depletion: 2006.
Michael Ponater, Dr., has been working for more than 15 years at the atmospheric dynamics department of DLR-IPA. His main expertise is in the field of radiative forcing, climate feedback, and climate
response, with special emphasis on climate impact modelling of non-homogeneously distributed trace
species. Between 2004 and 2007 he acted as a Visiting Professor at the Manchester Metropolitan
University due to his achievements in exploring aviation climate effects. With a record of about 40
peer-reviewed scientific papers, he has also contributed to several IPCC report chapters on the above
mentioned subjects.
Andrea Stenke, Dr. (PhD in 2006), scientist at DLR-IPA. She is experienced in developing ChemistryClimate Models (CCMs). She operates the CCM E39C-A which has been developed and implemented
at DLR. Her main scientific objectives are: stratospheric variability and trends, in particular with regard
to water vapour and ozone, Lagrange transport of tracers, validation of model data with respective
observations. She is already author and co-author of 8 peer-reviewed scientific papers.
5.1.3 MPI-M
Marco Giorgetta, Dr., leads the Global Climate Modelling Group at MPI-M and coordinates the Model
Integration Group developing the COSMOS Earth system model, which includes the ECHAM5 atmosphere GCM and the MPIOM ocean GCM. The research has been focused on the quasi-biennial oscillation in the tropical stratosphere (QBO), especially on the modelling of the QBO based on resolved
and parameterised wave-mean-flow interaction, and on the implications of the QBO for the general
circulation outside the tropical stratosphere. Coupled middle-atmosphere ocean models have been
used to explore the role of the stratosphere in the climate system. An important part of the work is the
further development of the atmospheric GCMs at MPI-M.
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
23
Hauke Schmidt, Dr., has worked on various aspects of chemistry and dynamics of the atmosphere
from the surface to the thermosphere and has authored or co-authored 29 scientific publications in this
field. He joined MPI-M in 2002. Currently, he is heading the research group on middle and upper atmosphere modelling at the MPI-M. He is also coordinating the DFG-funded German ARTOS project
on the “Atmospheric Response TO Solar variability”.
5.2 Cooperation with Other Scientists (Zusammenarbeit mit anderen Wissenschaftlern)
5.2.1 Collaboration with other projects of the Research Unit
In addition to the investigations of the specific science questions of SHARP-STC, the project will provide essential input to the other three projects. SHARP-STC will provide model data of the REF1 and
REF2 simulations as well as of the SCN2d simulation to Project 1 (SHARP-BDC) to analyse changes
in the Brewer-Dobson circulation, to Project 2 (SHARP-OCF) to understand the past evolution of
stratospheric ozone and to assess and interpret its future evolution, and to Project 3 (SHARP-WV) to
study past and future water vapour changes. The additional time-slice simulations will be performed in
SHARP-STC: SEN4 will help to interpret observed ozone changes in Project 2 (SHARP-OCF), while
SEN5 will support the interpretation of observed water vapour changes in project 3 (SHARP-WV).
SHARP-STC will use model data of the SEN0-3 simulations to be performed in Project 1 (SHARPBDC) to analyse the troposphere-stratosphere coupling in specific climate change scenarios. SHARPSTC will get long-term observational time-series of atmospheric composition and its changes from
Projects 2 and 3 (SHARP-OCF and SHARP-WV) to validate the CCMs and to explain past climate
change.
The CCM simulations will be supported by Dr. Christoph Brühl from the Max-Planck-Institut für Chemie
who is co-investigator of SHARP-WV.
5.2.2 Collaboration with other projects
FUB and MPI-M are participating in the DFG priority program CAWSES (Climate and Weather of the
Sun-Earth System). FUB coodinates the collaborative project ProSECCO (Project on Solar Effects on
Chemistry and Climate Including Ocean Interactions), with FUB and MPI-C as partners. One focus of
ProSECCO is the dynamical impact of decadal solar variability on stratospheric dynamics and the effects on tropospheric weather variability. MPI-M is participating with the ARTOS project investigating
the atmospheric response to solar variability in simulations with a general circulation and chemistry
model for the entire atmosphere (the HAMMONIA model based on ECHAM5). The research conducted in this project investigates specifically the vertical coupling of different layers of the atmosphere
from the lower thermosphere to the mesosphere, stratosphere and troposphere, based on chemistry
(ionised and neutral), radiation, dynamics and transport. Solar signals are analysed for the 27-day rotation period and for the 11-year solar cycle. Hence, the link to the CAWSES projects will provide
complementary knowledge to SHARP-STC on processes affecting the vertical coupling in the atmosphere.
The important task of developing and testing suitable models is widely acknowledged by the scientific
community and has been actively promoted by the World Climate Research Program (WCRP) SPARC
(“Stratospheric Processes and their Role in Climate”) through the two initiatives CCMVal (Chemistry
Climate Model Validation) and DynVAR (Dynamics and Variability) which encourage coordination and
communication between leading modelling groups worldwide. Modelling activities within SHARP will
be embedded into these international activities. CCMVal was a crucial driver for the modelling results
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
24
included in the 2006 WMO Ozone Assessment and will be a similar driver for the 2010 Assessment.
The transient REF1 and REF2 CCM simulations used in SHARP-STC (see also SHARP-BDC) will be
completed within the framework of the EC-funded project SCOUT-O3 (“Stratospheric-Climate Links
with Emphasis on the Upper Troposphere and Lower Stratosphere”).
Within the EC-project STRICT (“The Stratosphere in a Changing Climate and Implications for the Troposphere”; proposal for a Collaborative Project in the 2nd call of the 7th Framework Programme, February 2008) complementary model simulations are intended (incl. the CCMs E39C-A and
ECHAM5/MESSy) which would be available (if funded by the EC) to the SHARP consortium. The results from these simulations would enlarge the number of model ensemble simulations which would
enhance the reliability of statements.
5.3 Foreign Contacts and Collaborations (Arbeiten im Ausland und Kooperation
mit ausländischen Partnern)
DLR and FUB will extend their analyses to results of three external CCMs, the UKCA CCM run at University of Cambridge by Dr. Peter Braesicke and the UMETRAC and SOCOL CCMs run at NIWA
(New Zealand) by Dr. Greg Bodeker. Both partners will perform the CCMVal recommended REF1 and
REF2 simulations with their CCMs and provide data of these runs for the analysis in SHARP-STC.
Together with the CCMs used in SHARP this will enable to establish a small ensemble of models that
allows us not only to derive more reliable conclusions, for example of the future evolution of the BDC,
but also to provide uncertainty estimates. G. Bodeker will further provide a multivariate statistical
model for the analysis of the transient model simulations which will be implemented during a stay of G.
Bodeker at FUB in summer 2008.
Dr. Adam Scaife, lead scientist for Modelling Climate Variability at the Hadley Centre, UK Met Office
(UK), who is an expert in both stratospheric dynamics and tropospheric climate variability, has agreed
to collaborate as external partner. He will support the analyses of the observational and model data. A
first cooperation, in which existing idealised GCM results of FUB are analysed jointly, has been initiated recently.
Dr. Edwin Gerber, is a postdoctoral research scientist in the Dept. of Applied Physics and Applied
Mathematics at Columbia University, New York. He has a strong background in idealised modelling of
the atmosphere, with a general focus on intra-seasonal variability, in particular on the North Atlantic
Oscillation and Annular Modes. To investigate the link between the stratosphere and troposphere, he
developed an idealised General Circulation Model (GCM) that captures the key features of coupling on
intra-seasonal time scales. He will support the studies on stratosphere-troposphere dynamical coupling in SHARP-STC with simulations of his idealised GCM.
5.4 Scientific Equipment Available (Apparative Ausstattung)
5.4.1 FUB
FUB is running and analysing the CCM simulations on the high performance computers of FUB, the
Norddeutscher Verbund für Hoch- und Höchstleistungsrechnen (HLRN) in Berlin, and Deutsches Klimarechenzentrum (DKRZ) in Hamburg without extra costs. For testing and post-processing a local
workstation cluster is available. A fully equipped PC workplace will be provided.
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
25
5.4.2 DLR
Provision of fully equipped PC workplace; access to DLR workstation cluster and super-computers
(currently NEC-SX6).
5.5 General Contribution of the Institutions (Laufende Mittel für Sachausgaben)
Freie Universität Berlin and Deutsches Zentrum für Luft- und Raumfahrt e.V. will cover for their part
the current expenses during the project.
5.6 Conflicts of Interest with Economic Activities (Interessenskonflikte bei wirtschaftlichen Aktivitäten)
None
5.7 Other Requirements (Sonstige Voraussetzungen)
None
6
Declarations (Erklärungen)
A request for funding this project has not been submitted to any other addressee. In the event that we
submit such a request, we will inform the Deutsche Forschungsgemeinschaft immediately.
Prof. Dr. R. Bohnsack ([email protected]), ‘DFG-Vertrauensdozent’ at Freie Universität
Berlin, has received a copy of this proposal.
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
7
Signatures (Unterschriften)
PD Dr. Ulrike Langematz
Prof. Dr. Martin Dameris
Antragsteller FUB, Principal Investigator
Antragsteller DLR, Co-Investigator
Prof. Dr. Ulrich Cubasch
Dr. Marco Giorgetta
Antragsteller, FUB, Co-Investigator
Antragsteller MPI-M, Partner
26
SHARP Project 4: Stratosphere-troposphere coupling in a changing climate (SHARP-STC)
8
27
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