Impact of INSAT-3D radiance data assimilation using WRF 3DVAR on simulation of Indian summer monsoon and high-resolution rainfall forecast over hilly terrain

This study describes the impact of assimilation of INSAT-3D radiances data from both imager and sounder for Indian summer monsoon simulation and rainfall forecast over a hilly terrain using Weather Research Forecast model and its three-dimensional variational data assimilation (3DVAR) technique. The assimilation experiments conducted for the whole month of July 2016 reveal the superior impact of radiance data assimilation (DA) on analysis and forecast of the vertical profile of wind and temperature than the conventional DA experiment. Compared to the rest of the experiments, the imager DA experiment significantly improves the wind forecasts throughout the troposphere and ameliorates the temperature forecasts from 950 to 450 hPa. The sounder DA shows more improvement in the upper-level temperature forecast compared to the imager DA experiment. In addition, the spatial representation of low-level jet, temperature and moisture fields shows more relative improvement in the experiments with radiance DA than conventional DA experiments. While the impact of imager DA is superior for low-level jet forecast, the sounder DA reveals a more accurate tropospheric temperature and relative humidity forecast compared to the rest of the experiment. The rainfall forecast has also improved significantly with radiance DA over the Indian continent, mainly in India's northern, eastern and northeastern regions. Further, India’s northeastern region’s high-resolution rainfall forecast illustrates improvement using INSAT-3D radiance DA from both imager and sounder together compared to only conventional DA.