All-sky microwave humidity sounder assimilation in the Korean Integrated Model forecast system

The Korean Integrated Model (KIM) and hybrid data assimilation system were extended to assimilate all-sky radiance from microwave satellite sensors. Initially, a radiative transfer model for the TIROS Operational Vertical Sounder (TOVS), called RTTOV-SCATT (version 11.3), was implemented to assimilate the Microwave Humidity Sounder (MHS) 183 GHz channels over the ocean. Cloud and precipitation parameters are not directly assimilated into our system, but temperature and humidity profiles are improved in the all-sky assimilation. In the cycled analysis and forecast experiments, an assimilation of the MHS in a cloudy region shows globally substantial benefits: the coverage of the MHS radiance data is increased by 23-28% in the all-sky assimilation. It is demonstrated that RTTOV-SCATT well describes the brightness temperature (TB) on selected cloudy pixels over the Tropics and the Southern Hemisphere, with potential for linking the TB innovation to the increment for the hydrometeor variable. As a result, a reduction of 1.11% in the specific humidity root-mean-square error occurs in the 6-hr forecast field as compared to the European Centre for Medium-Range Weather Forecasts (ECMWF)'s Integrated Forecasting System (IFS) analysis. Even though the all-sky MHS assimilation's impact on the Northern Hemisphere midlatitudes is not remarkable, it nonetheless produces an improved humidity analysis increment for a heavy rainfall case over East Asia.