Use of AMSU data in the Met Office UK Mesoscale Model

In common with other global NWP centres, assimilation of radiances from the ATOVS instrument package at the Met Office results in a large benefit to global NWP forecasts (English et al., 2000) and has been used operationally since mid-1999 in the Met Office global 3D-Var system. Recently work has been carried out to assess the impact of using radiances from the AMSU A&B instruments in the UK Mesoscale Model (UK Mes). This is a limited area model with a domain covering the British Isles (the region is shown in the right panel of Figure 1) and to date its assimilation scheme has mainly used conventional observations. For the initial implementation of AMSU data in the UK Mes we have used the pre-processing scheme for ATOVS radiances in the global model as closely as possible to avoid duplication and maintenance of computer code. However some departures are necessary and these are described in the following sections.