A Simplified 4D-Var Vortex Model to Improve 0−12-h Hurricane Intensity Forecasts through Assimilation of Satellite Microwave Retrieval Products

Much more improvements have been obtained for the forecasts of hurricane track than intensity. The intensity forecast, especially during the first 6-12 forecast hours, is extremely challenging due to a lack of observations and/or an inability for model to capture vortex features inside hurricanes. Microwave imagers, temperature sounders and humidity sounders provide unique radiance measurements for observing oceanic surface properties and vertical atmosphere temperature and humidity profiles in almost all weather conditions except for heavy precipitation. For examples, the Advanced Microwave Scanning Radiometer 2 (AMSR2) observes radiation emitted from the Earth surface that could be used to retrieve sea surface temperature (SST), sea surface wind (SSW), column integrated total precipitable water (TPW), liquid water path (LWP) and other variables. The Advanced Technology Microwave Sounder (ATMS) measure radiances at multiple frequencies to provide information about the vertical profiles of atmospheric temperature and humidity. In this study, a simplified four-dimensional variational (S4D-Var) vortex initialization and assimilation system is built, consisting of a non-hydrostatic axisymmetric hurricane model, its tangent linear and adjoint models, and several observation operators for satellite microwave geophysical retrieval products for hurricanes. Improvements in hurricane intensity forecast during the first 6-12 forecast hours are demonstrated by the S4D-Var system and the Hurricane Weather Research and Forecasting (HWRF) model with the S4D-Var generated vortices incorporated.