Added Value of Assimilating Radar Reflectivity to All-Sky Infrared Radiances for Analyses and Forecasts of Tropical Cyclone Intensity

Tropical cyclones (TCs) spend most of their life cycle over the ocean, where conventional in situ observations are sparse. Remote sensing observations from satellites and radars provide an effective way to overcome this limitation and have become essential for improving TC analyses and forecasts. But studies that simultaneously assimilate both infrared radiances and radar reflectivity for TCs remain limited. In this study, simultaneous assimilation of hyperspectral infrared radiances onboard a geostationary satellite and reflectivity observations from an airborne radar is investigated, especially for the added value of assimilating radar reflectivity for analyses and forecasts of TC intensities. Based on non-cycled observing system simulation experiments (OSSEs), results show that assimilation of infrared radiances mainly improves state variables of temperature and specific humidity, while assimilation of radar reflectivity substantially enhances the wind field. The advantages of simultaneously assimilating infrared radiances and reflectivity observations are demonstrated, which leads to dynamically coherent and balanced analysis increments and TC structures. Furthermore, compared to assimilating either infrared radiances or reflectivity observations, simultaneous assimilation of them produces more accurate analyses and forecasts of state variables and TC intensities. These findings highlight the complementary strengths of satellite and radar observations and provide insights for observing strategies for TCs.