[10-5]

Improved use at the Met Office of SEVIRI infrared observations in cloudy regions

R. Tubbs (Met Office) , P. Francis (Met Office)

Since 2008, Met Office regional models have used cloud information from offline cloud analyses in operational variational data assimilation. In many situations, the offline cloud analysis is strongly constrained by the NWP model fields used for the cloud analysis, and when the resulting cloud data are assimilated into a different NWP model this leads to an undesired link between the models. This makes robust, independent trialling of changes to the NWP models difficult. In order to alleviate the problem, and also to improve forecast accuracy, a new approach has been developed for assimilating cloud information from geostationary infrared satellite radiances. The cloud-top pressure is estimated from the satellite radiances and the latest 1.5km-resolution UKV model background fields within the component of the UKV NWP system which performs observational quality control and bias correction (OPS). This information is then assimilated in the UKV 3D-Var analysis. We describe the approach used for extracting cloud-top pressure information from SEVIRI radiances, and will present results from trials of assimilating this information into the Met Office UKV 1.5km NWP system. Also discussed are trial results using the same cloud information to select water vapour channel observations with little cloud-contamination for clear-sky radiance assimilation.