All-sky assimilation of infrared and microwave radiances for four tropical cyclones

Satellite infrared (IR) and microwave (MW) radiances provide complementary information on tropical cyclones (TCs), with IR radiances informing on cloud locations, sizes, and cloud-top heights, and MW radiances conveying information on hydrometeor phase, amount, and location below cloud tops. This study utilizes real-data experiments to investigate the impact of assimilation of MW all-sky radiances, in addition to IR radiances, on four major TCs that impacted the U.S. during the 2017 Atlantic hurricane season. Furthermore, impacts of the microphysics parameterization scheme (MPS) are assessed with two schemes, the Weather and Research Forecast model single-moment-6-class (WSM6) MPS and the Thompson et al. (2008; THO) hybrid MPS. These MPSs lead to little difference in data assimilation analyses and forecasts when only conventional observations are assimilated. However, when satellite all-sky IR radiances are assimilated, a significant portion of analyzed TCs in the WSM6 experiments are notably stronger whereas most of the TCs in the THO experiments are weaker than best track. This discrepancy is closely linked to differences in cloud-top features produced by the two MPSs and the impact of these differences on the calculated IR radiances. However, regardless of the MPS used, the additional assimilation of MW radiances improves forecast performance, especially on intensity, compared to when they are not assimilated.