Application of ATOVS radiance assimilation to numerical simulation of a mesoscale heavy rainfall

Based on ATOVS data and conventional sounding data, two assimilation experiments are performed to simulate a heavy rainfall over the middle-lower reaches of Yangtze River and the east of southwest China from June 22 to 24 in 2004 by using model MM5. In the NOATOVS experiment, only conventional sounding data are assimilated based on the successive correction scheme, while in the ATOVS experiment, the ATOVS radiance data are assimilated by using the GRAPES (Global and Regional Assimilation and Prediction System) 3D-Var system. The effect of the radiance data on the background field is analyzed. It indicates that direct assimilation of ATOVS radiance data could improve the temperature, humidity and wind fields within the troposphere. Moreover, the comparison between the results of the two experiments shows that ATOVS experiment can not only simulate the circulation pattern well, but also describe the intensity and the distribution of the rainfall better than the NOATOVS experiment.