Sensitivity Differences Between 118 GHz and 183 GHz Radiance in All‐Sky Assimilation With Hydrometeor Control Variables and the Impact on a Typhoon Structure Forecast

Abstract All‐sky microwave radiance assimilation plays a crucial role in numerical weather prediction, with the 183 GHz absorption band recognized for its strong sensitivity to humidity and clouds, and the 118 GHz absorption band primarily responsive to temperature but also sensitive to hydrometeors. The Microwave Humidity Sounder‐II (MWHS‐II) aboard the FengYun‐3 satellite includes channels near both bands, offering complementary capabilities. Although the assimilation performances of instrument channels in these bands have been studied, their comparative impacts on hydrometeor fields remain insufficiently explored. Through the separate and joint assimilation of 118 and 183 GHz MWHS‐II channels using hydrometeor control variables, this study investigates how directly adjusting hydrometeor analysis for thermodynamic consistency influences the analysis and forecasting of Typhoon Lekima (2019). Results show that the 183 GHz band has higher sensitivity to solid hydrometeors at higher levels, whereas the 118 GHz band is more sensitive to liquid hydrometeors at lower levels. These differences are clearly manifested in the hydrometeor analysis. Joint assimilation of both sets of channels improves the representation of temperature, humidity, and hydrometeor distribution. This not only enhances the analysis and forecasting of typhoon intensity but also deepens the understanding of typhoon structure. In particular, the sensitivity of the 183 GHz band to solid hydrometeors provides valuable insights into their role in the secondary eyewall formation for Typhoon Lekima (2019). With the use of hydrometeor control variables, the synergistic assimilation of MWHS‐II channels demonstrates potential for advancing tropical cyclone analysis, forecasting, and understanding of dynamics.