Impact of assimilating atmospheric motion vectors from Himawari-8 and clear-sky radiance from FY-4A GIIRS on binary typhoons

Binary typhoons (Maysak and Haishen) uncommonly hit northeastern China in 2020, which brought historical extreme precipitation to this region within less than a week. The impact of high-frequency (15-min) assimilating atmospheric motion vectors (AMVs) from Himawari-8 and clear-sky radiance from Fengyun-4A (FY-4A) Geostationary Interferometric Infrared Sounder (GIIRS) on this rare case has been investigated based on the Weather Research and Forecasting Model (WRF) and three-dimensional variational (3D-Var) data assimilation system. The study indicates that the dynamic adjustment is obvious from assimilated hourly AMVs information, but it still needs to be combined with the 15-min FY-4A thermal field adjustment, which is essential for better forecast simulations of minimum sea level pressure (MSLP) and landfall precipitation. A detailed typhoon structure is accurately reproduced for Maysak (Haishen) with fewer (more) anomalies of upper-level warm temperatures and lower-level negative geopotential heights in the decay (intensification) phase. Meanwhile, the performance of three hourly landfall precipitation by Maysak is evaluated with better spatial distribution and higher equitable threat scores (ETS) for the large threshold (20 mm), resulting from wet bias reduction by much drier water vapor conditions in the analysis and more precise forecasts of relative humidity, water vapor transportation, and its divergence. However, it achieves neutral to negative impacts on track forecasts for Maysak and wind simulations at different levels. This research may provide guidance for monitoring and forecasting typhoons of assimilation from different satellite information in mid-to-high latitude regions in East Asia.