The Potential Benefits of Assimilating Future CubeSat-Constellation Microwave Radiances on Regional NWP for Typhoon and Heavy Rainfall With a Rapid-Update Convection-Permitting 4DEnVar

Abstract

The microwave sounding instruments have been providing humidity and temperature profiles critical for improving numerical weather prediction (NWP). In recent years, advanced microwave sounders have been proposed to be onboard future CubeSats that are less expensive than traditional satellites, providing unprecedented rapid-update and low-earth-orbit microwave observations that can follow the evolution of the typhoon and convective weather systems. In this study, the potential values of assimilating future CubeSat constellation microwave radiances in clear-sky condition for regional NWP are preliminarily assessed with observing system simulation experiments using the convection-permitting 4DEnVar for the prediction of typhoon “Infa” and its associated “7.20” heavy rainfall event that occurred in China in July 2021. This constellation is assumed to include 12 CubeSats equipped with microwave sounders obtaining radiances sensitive to water vapor and temperature. The results show the CubeSat constellation radiances demonstrate positive impacts on the analyses and forecasts of typhoon's track, intensity, precipitation, and dynamical conditions. The forecast errors of typhoon's maximum wind speed, minimum sea level pressure, and track are reduced by 17.9%, 14.3%, and 27.9%, respectively. The wind, temperature, and humidity of 6-hr forecasts are improved by 4.95%, 7.89%, and 5.17%, respectively. The rainfall forecast scores in terms of fraction skill score and equitable threat score are also improved by 7% and 5.9% with the ameliorative prediction of magnitude and pattern of rainfall maximum centers for both the landfall typhoon and “7.20” heavy rainfall event. This study indicates the potential benefits of microwave radiances from a low-earth-orbit CubeSat constellation with rapid revisits using advanced data assimilation on the regional NWP in the future.