Assimilation of radiance products from geostationary satellites: 1-year report

Assimilation of radiance products from geostationary satellites: 1-year report
Date Published
EUMETSAT/ECMWF Fellowship Programme Research Reports
A. McNally
Abstract Following the replacement of GOES-12 by GOES-13 on April 2010 and the replacement of MTSAT-1R by MTSAT-2 on August 2010 work has been directed towards incorporating Clear Sky Radiances (CSR) from GOES-13 and MTSAT-2 on the operational ECMWF system. This report gives an overview of the assimilation strategy of CSR from GOES-13 and MTSAT-2 and summarizes the results of monitoring and assimilation experiments performed to asses the impact of new CSR data sets on analysis and forecast quality. An evaluation of data from GOES-13 has demonstrated that the radiances have reduced biases relative to data from GOES-12. An evaluation of data from MTSAT-2 has confirmed that the radiances are of very similar quality to those from MTSAT-1R. During the evaluations of GOES-13 and MTSAT-2 it has again been confirmed that geostationary radiance data enhance the quality of the ECMWF analysis and improve the fit to other independent observations. The impact of geostationary radiances on headline forecast measures remains rather small. The second part of this study involves the use of all-sky radiance product (ASR) from Meteosat-9 SEVIRI observations. The overcast cloudy scheme used operationally at ECMWF to directly assimilate cloud-affected infrared radiances from AIRS/IASI and HIRS polar orbiter data has been successfully extended to assimilate cloud affected radiance observations from SEVIRI. Preliminary results show that cloud parameters derived from the SEVIRI ASR inside the ECMWF 4D-Var agree extremely well with independent pixel-by-pixel estimates from EUMETSAT processing. Assimilation experiments with overcast SEVIRI radiances have been shown to provide information on temperature and humidity in addition to that provided by the clear-sky observations. The main aim of this study is to extend the humidity tracing capability, previously demonstrated only in clear sky, to cloudy regions, to obtain an all-sky constraint the atmospheric wind field with geostationary radiances.