A comparison of the performance of Kalpana and HIRS water vapor radiances in the WRF 3D-Var assimilation system for mesoscale weather predictions

Abstract

[1] An impact study is presented to compare the performance of the Weather Research and Forecasting (WRF) model in response to assimilation of water vapor (WV) channel radiances from Indian geostationary satellite Kalpana and from High-Resolution Infrared Sounder (HIRS) HIRS-3/4 instruments on board NOAA satellites. A three-dimensional variational data assimilation (3D-Var) system is used for assimilation of radiances from above mentioned instruments, and the impacts of these radiances were assessed on 24 h forecasts starting on each day at 0000 UTC for the period 10–20 July 2008. It was found that the Kalpana radiances provide significant improvement over the HIRS radiances. Compared to HIRS, the assimilation of the Kalpana WV radiances improved the mid–upper tropospheric moisture (∼6%) and temperature (∼1.5%) analysis when verified against National Centers for Environmental Prediction (NCEP) analysis. Simulated microwave radiances using model fields assimilated with Kalpana radiances match significantly closer to Advanced Microwave Sounding Unit-B (AMSU-B) radiances, compared to those assimilated with HIRS radiances. Impact on mid–upper tropospheric moisture, temperature and lower and upper tropospheric wind forecast was positive. The reduction in the root mean square errors by the Kalpana radiance assimilation reached up to 1.5% for the temperature forecast against NCEP analysis, and about 2% for the moisture forecast. The improved mid to upper tropospheric humidity and temperature with the use of Kalpana radiances led to better rain forecasts.