Assimilation of cloud-affected radiances from Meteosat-9 at ECMWF

Assimilation of cloud-affected radiances from Meteosat-9 at ECMWF
Date Published
EUMETSAT/ECMWF Fellowship Programme Research Reports
Document Number
A. McNally
Event Series/Collection
EUMETSAT/ECMWF Fellowship Programme
Abstract This report summarises the evaluation of cloud-affected SEVIRI radiances for use in the operational assimilation system at ECMWF. The ECMWF 4D-Var analysis system has been successfully extended to directly assimilate cloud-affected SEVIRI radiances in overcast conditions, in addition to the clear-sky data from Meteosat-9. We discuss results to characterise how these radiances affect the wind analysis via 4D-Var tracing, and compare the impact to that of the assimilation of clear-sky radiances and cloudy AMVs from SEVIRI. Experiments with overcast SEVIRI radiances in addition to the clear-sky data set from Meteosat-9 have a positive impact on wind analysis through the troposphere with a better performance than clear-sky radiances over the Southern Hemisphere in the upper-troposphere.The potential operational benefits of assimilating overcast radiances from Meteosat-9 in addition to the clear radiances have been also assessed in a full system where all routinely available observations are used. Results are clearly positive and the operational switch to ASR from Meteosat-9 in the next coming cycle (CY38R1) should improve the quality of 4D-Var analyses and subsequent forecasts. The assessment of the impact of all-sky SEVIRI observations in the operational assimilation and forecast system is also presented in terms of DFS diagnostics and forecast error contribution.