Assimilation of ATOVS radiances at ECMWF: Third Year EUMETSAT Fellowship Report
Di Tomaso, E. ; Bormann, N. ; English, S.
This report summarises work towards a general enhancement of the usage of satellite microwave observations at ECMWF. Three different topics are discussed: the evaluation of new instruments, the enhancement of observations at high latitudes, and the characterisation of an error model for observations sensitive to the surface. The quality of the microwave sounder data from the recently launched Metop-B satellite has been evaluated through a comparison with simulated radiances from the model state. Statistics of first-guess departures show that both AMSU-A and MHS sensors are in very healthy conditions. As result of these studies the two Metop-B microwave sounders have been actively assimilated at ECMWF since 10 December 2012. We have tested an enhanced assimilation of AMSU-A and MHS observations at high latitudes. A considerable number of humidity and temperature observations have been assimilated in data-sparse areas of the globe with a significant impact on forecast of all relevant atmospheric variables. These changes will be implemented at ECMWF in the next cycle upgrade (CY39R1). We have estimated a surface-dependent observation error for AMSU-A channel 5 (the lowest peaking channel among the actively assimilated AMSU-A channels at ECMWF) which takes into account the observation sensitivity to the surface and the emissivity errors of different types of surfaces. This study provides an initial base for future work towards a more efficient usage of surface-dependent observations.
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