Abstract:
The Korean Integrated Model (KIM) has been enhanced to assimilate all-sky radiance from microwave humidity sensors (MHS and MWHS-2) using hybrid four-dimensional ensemble variational data assimilation (Hybrid-4DEnVar). RTTOV-SCATT version 13.0 was implemented for all-sky radiance assimilation, and the observation preprocessing system was significantly modified. This study presents a preliminary assessment of the performance of all-sky radiance assimilation in the operational KIM (version 4.0) forecast system. The assimilation of all-sky radiance incorporates additional observations in tropical regions, leading to increased moisture increments and reduced humidity analysis errors in dry-biased tropical areas. This improvement in the initial humidity field over the tropics gradually propagates to the mid-latitudes during the forecast. However, the degradation of the initial temperature field resulting from all-sky radiance assimilation is more pronounced in the mid-latitudes and propagates poleward during the forecast. Additionally, observation-based verification shows a decrease in the O-B standard deviation for humidity sensors but an increase for temperature sensors.

Citation:
Lee S. H., Jeong H. B. (2025). Development and initial performance verification of All-Sky Microwave radiance assimilation in the operational KIM Forecast system. koreascience.or.kr.