The assimilation of the ATOVS radiances on the global 3 dimensional variational (3DVar) system has been developed at Japan Meteorological Agency (JMA). Several procedures has been developed: an advanced thinning to even account for more than one satellites, the detection of clear/cloud/rain conditions, the removal of the radiances which cannot be simulated using a current radiative transfer model or numerical weather prediction (NWP) model, the assignment of observation errors according to the observation conditions, and the correction of a radiance bias with minimized effect from a NWP model bias.
Parallel experiments proved the ATOVS assimilation is significant improvements over the previous ATOVS retrieval assimilation in many respects. Analyzed temperature and water vapor are improved verified against radio sonde observation and Special Sensor Microwave/Imager (SSM/I). Impacts on forecast are positive in the southern hemisphere and neutral in the northern hemisphere on the whole. Especially greatly positive impacts are shown for the short term forecast for both the hemisphere and the tropics.
As a result of these findings, ATOVS radiance has been assimilated operationally since 28 May 2003.