Progress report The Met. Office contribution to PROMISE Sep 2000 A pair of AGCM sensitivity experiments have been designed and run, with the aim of assessing the impact of SST anomalies in the Mediterranean on seasonal (July-September) rainfall totals over the Sahel. They confirm that the Mediterranean does indeed have a significant impact on the Sahel, and are currently being used to understand the mechanisms involved. (Dave Rowell) During the past year, a new boundary layer mixing scheme has been implemented in The Met. Office's Unified Model (UM), and the vertical resolution in the lower troposphere has been increased nearly threefold. Recently, a set of major revisions to UM's convection scheme has been put together to improve the interaction between the convection and boundary layer schemes and to reduce the sensitivity of the convection scheme to the increased vertical resolution.ã The modifications include improving the diagnosis, triggering and treatment of shallow and deep convection (using information from the boundary layer scheme), as well as correcting long-standing errors in the scheme. One of the most important aspects of this revised version is that convection is forced to trigger from the lifting condensation level when convection is diagnosed. These revisions have now been tested in the climate and global forecast models. The distribution of shallow and deep convection appears to be realistic, and there are some improvements in the monsoon circulation and the precipitation distribution, although there are problems with excessive low level layer cloud forming in the shallow convective layer and an overall spin-upã of the model's Hadley circulation. A long (50+ years) run of the climate model including these revisions will be started shortly. This will be compared with parallel runs of the previous model version in order to assess the impact of these changes on the mean and interannual variability of the summer monsoons. (Gill Martin) Work has proceeded on finalising the configuration of the Met. Office coupled and uncoupled GCMs to be run to seasonal range under the EU DEMETER project. Installation of the models on the ECMWF Fujitsu is under way with testing expected to start, as scheduled, in September. In liaison with PROMISE and DEMETER colleagues, a list of the required model output diagnostics has been drawn up. A schedule of the coupled and uncoupled experiments planned by the Met. Office, and the output that will be available for the PROMISE archive, has been provided for the PROMISE website. (Richard Graham) Code was written to enable seasonal variation of vegetation parameters to be prescibed in the new MOSES2 land surface scheme of the UM. Analysis was carried out on the dieback of the Amazon rainforest in coupled climate-vegetation simulations with the Hadley Centre GCM, and preliminary results presented at the EGS meeting in Nice, France (25th-28th April 2000).ã A literature review of Amazonian climate change in other GCMs was made, and it was found that several GCMs also produce future drying of Amazonia.ã In these models, Amazon drying appears to be associated with El Nino-like patterns of SST change in the Pacific under a warming climate.ã (Richard Betts)ããããããããã |