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MEETING REPORTS |
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Report of the EuroGRIPS Meeting held at CNRM, Toulouse, 26- 27 September 1996
Introduction
The SPARC programme of the WCRP has defined several initiatives, one of which is an evaluation of the performance of general circulation models (GCMs) that can resolve the stratospheric circulation. The GRIPS initiative (GCM-Reality Intercomparison Project for SPARC) is open to all groups or individuals who run such models: the only restriction for participants is that their model must include a realistic representation of the hydrological cycle and a full radiation scheme, so that it can be used as a fully interactive climate model. EuroGRIPS is the European contribution to GRIPS and is a two-year project funded by the EU Framework IV programme.
This meeting provided an opportunity for the participants (FU-Berlin, CNRM in France, UKMO and UGAMP) to discuss the current status of the project and outline future work, both within the EuroGRIPS contract and beyond. The first day of the meeting was devoted to presentations from each participant; the second to discussing future work. An international GRIPS workshop is to be held in Berlin in early March 1997, for all groups working on the international GRIPS project (including the four EuroGRIPS groups). Another EuroGRIPS meeting will be held in a year or so, probably in Reading
Current EuroGRIPS status
CNRM:
Results from the ARPEGE/CLIMAT V2 GCM were shown. Significant features in V2 (as opposed to V1) are the modularity of the code, the option of stretched coordinates and the Morcrette radiation scheme. Most of the data presented came from T42L41 runs (T21 and T106 runs had also been done): the model top is at ~80 km and the vertical resolution in the stratosphere is ~2km. The model has a cold bias at the tropical tropopause which is partially removed by the use of the Morcrette radiation scheme in V2. In general, the model variability is much lower than in the ECMWF climatology, and V2 has a weak cold bias in the stratosphere (based on averaging 10 Januarys).
The model (V1 at T21 resolution) was used to study tropical waves. The model was seen to reproduce these waves, and their intensity and frequency were comparable with observations. Future work will involve looking at these waves in V2.
Transport processes in the middle atmosphere of a GCM were discussed. It is planned to investigate the tropics (the subtropical 'barrier'; excitation of tropical waves; mixing in the lower stratosphere), the polar stratosphere (fragmentation and laminae in southern winter), and the representation of global 'normal modes'.
Studies of stratospheric chemistry in which the ARPEGE/CLIMAT V2 was coupled to the REPROBUS chemical-transport model were shown. Future studies will involve extending the chemistry to the troposphere and calculating the climate impact of ozone changes in the stratosphere and the troposphere.
FU-Berlin:
The FU-Berlin spectral model (which derives from the ECMWF model and includes physical parametrizations based on those of the Hamburg climate model) was run at T21L34 (top at 83 km) for a 28 year control experiment. The radiation scheme is that of Morcrette; absorption of solar radiation due to O2 and O3 above 70 hPa is as in Shine & Rickaby (1989); there is Newtonian cooling in the infrared above 10 hPa. The GCM climatology, its tropical SAO (the westerly phase is present in the model, but it is weak), and its stratospheric major warmings, have been studied in recent papers (Langematz & Pawson 1996, Muller et al. 1996, Erlebach et al. 1995, respectively). Validation of parametrizations in the model are discussed in Pawson et al. (1996). The FU-Berlin will carry out a new integration at T21L34 with a new radiation scheme and a new ozone climatology. This run will be at least 10 years long and will have sea- surface-temperatures (SSTs) without interannual variability.
UKMO:
Results from two recent UM runs done in collaboration with UGAMP were discussed (the first run is 15 months long; the second run has now run for 5 years), and compared with the UKMO analysis. The UM is grid-point and the version used has a resolution of 2.5o latitude by 3.75o longitude in the horizontal, and has 49 levels in the vertical. The main results were: the UM has a cold bias in the stratosphere; the polar night jet is too strong (N.B. the UM uses Rayleigh friction above about 20 hPa); the polar night jets are upright and do not tilt equatorward; the UM has no QBO and has an SAO but its westerly phase is weak.
Future work will involve analysing data from the second run, and working with new versions of the UM to:
(a) improve the vertical resolution around the tropopause and in the troposphere (in line with likely changes to the standard climate model) - there are no immediate plans to extend the model upwards or improve the stratospheric resolution;
(b) use the new T3E computer -- this will probably happen at the beginning of 1997;
(c) do a 10 year run for GRIPS with HADAM3 physics (including the Edwards and Slingo radiation scheme);
(d) incorporate new dynamics. This work forms part of the GRIPS plans to look at the effect of improving the representation of the stratosphere on the simulated climate (and the possible impact on medium-range forecasts).
UGAMP:
Results from an 8 year run of the EUGCM at T21L47 resolution were shown (this run is now 10 years long). The main results were: the EUGCM has a cold bias in the stratosphere; southern winter starts late and finishes late (typically by about one month); the EUGCM consistently develops stratospheric warmings during northern winter - at T21 their structure is unrealistic (e.g. they do not allow the vortex to recover and cause the final warming to occur too early) and at T42 it is more realistic (Fig. 36); the polar night jet is too strong using Rayleigh friction - this improves when a variant of the Palmer et al. gravity wave drag scheme is used; the polar night jet tilts equatorward (when a variant of the Palmer et al. scheme is used; with Rayleigh friction the jets are upright); the EUGCM does not have a QBO and its SAO has a weak westerly phase; the EUGCM has a 2-day wave (Norton and Thuburn, 1996)
Future work
EuroGRIPS:
- 1. Document the models using an agreed format (the UKMO and the UGAMP groups have already done this).
- 2. EuroGRIPS participants to gather together standard fields of ozone, temperature and other trace gases for use in standard tests of the radiation schemes (by early 1997). These tests will look at cross-sections of heating rates derived from different radiation codes and standard profiles, and compare them with line-by-line calculations. UKMO and UGAMP will do work along these lines by comparing the Edwards and Slingo scheme with other schemes now in use (e.g. MIDRAD in the EUGCM).
- 3. If time allows, the EuroGRIPS participants to look at sudden warmings and their relation- ship with the troposphere (available data to be brought to GRIPS meeting in March 1997).
- 4. EuroGRIPS groups to carry out gravity wave drag experiments as defined at the Victoria GRIPS workshop: using (a) no drag; (b) fixed drag; (c) own drag.
- 5. Liaison with the AMIP project. This is still under discussion.
- 6. Couple chemistry and transport models with GCMs. CNRM has been working on this area. J. Austin at the UKMO (not linked with EuroGRIPS) has been working on incorporating chemistry in the UM (this is a long-term aim).
In September 1996 there was a SPARC stratospheric climatology meeting to compile a reference climatology using the best available stratospheric data sets. R. Swinbank from the UKMO, and a member of EuroGRIPS, attended the meeting and produced a report. FU-Berlin has set up a EuroGRIPS Web Site. Dr. Pawson gave a talk on EuroGRIPS at SPARC 96.
ASCHAM
All participating groups expressed their interest in continuing EuroGRIPS by applying for EU funds for a project to follow EuroGRIPS. The ASCMAM (Assessment of Climate-Middle Atmosphere Models) project has been submitted to the EU.
William Lahoz and
Ding Ming Li
(Reading)