Mesoscale Model Upgrade - Introduction of the land surface tile scheme (MOSES 2)
Best, M.J. ; CHALCRAFT, B.V. ; Bornemann, F. Jorge ; WILSON, C.A.
The Met Office Surface Exchange Scheme (MOSES 1) was introduced into the operational U.K. mesoscale model in May 1999 and into the global model in June 2000. This report discusses the upgrade to the mesoscale model to MOSES 2, which allows for non-uniformity of the land surface in a grid box. Each box may be split into up to 9 different types (tiles) and separate fluxes and temperature calculated for each, before amalgamating their effects on the atmosphere. The scheme was tested for 16 cases, with full data assimilation for 12 hours and with forecasts to 48 h. The overall impact as measured by the 5-component U.K. Index is 1.68 points using all stations in the whole of the mesoscale area, 1.55 points for WMO block 03 stations and 0.44 if just restricted to the 41 UK index stations. The latter estimate is generally less reliable due to the small sample of verification observations for 16 cases only and so the impact is more likely to be closer to the estimate for WMO block 03. The main improvements are to 10 m winds and screen temperatures. Two weeks of trial suite running, in parallel with the operational version, was also carried out and with accompanying objective verification and subjective assessment. The ...
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