Operational use of ATOVS radiances in global data assimilation at JMA

1. Introduction The Advanced TIROS Operational Vertical Sounder (ATOVS) radiances have been operationally assimilated in the Japan Meteorological Agency (JMA) global 3D-Var data assimilation system since 28 May 2003. It replaced TOVS/ATOVS retrievals, which had been assimilated in the JMA global data assimilation system. The direct assimilation of ATOVS radiances is superior to its retrieval assimilation because the retrievals have some error in their conversion from radiance to analysis variables such as temperature and relative humidity. Data assimilation experiments, which was conducted before the operational use of ATOVS radiances demonstrated significant impacts on forecasts and analyses. This report describes the ATOVS data used at JMA and some results of the assimilation experiments.