Development of a 3D Variational Assimilation System for ATOVS Data in China

A new 3D variational data assimilation system (GRAPES-3Dvar) with the emphasis on effective usage of satellite data has been developed in China. The forward observational operator and its tangent linear and adjoint for satellite radiances are adopted from the software package RTTOV developed by ECMWF. A bias correction scheme for input radiances is also developed. At present only AMSU-A and AMSU-B data over the oceans are used to avoid the influences of inaccurate computation of surface emissivity and erroneous first guess at higher levels. In the experiments of typhoon case studies, the assimilation of ATOVS data results in better analyses of both the inner structure of the typhoon and the large scale environment, and improves the numerical prediction of track and intensity of the typhoon. The assimilation system will be tested in an operational environment