Assimilation of All-Sky AMSU-A and GMI Radiances with the NCEP GSI-Based Ensemble-Variational Hybrid Data Assimilation System: Impact on Numerical Simulations of Hurricane Florence (2018)

The impacts of assimilating all-sky microwave satellite radiances from the Advanced Microwave Sounding Unit-A (AMSU-A) are evaluated during numerical simulations of the rapid intensification and weakening stages of Hurricane Florence (2018) from 03 to 07 September 2018. The Weather Research and Forecasting (WRF) model and the NCEP Gridpoint Statistical Interpolation (GSI)-based three-dimensional variational (3DVar) hybrid data assimilation system are employed. Results show that assimilation of the clear-sky or all-sky AMSU-A radiances produces positive impacts on the intensity forecasts. These improvements are likely due to the consecutive positive increments of relative humidity and tangential winds within the low-level inner-core regions after assimilating satellite radiances. However, none of the experiments predict the weakening process of the hurricane correctly. Further diagnosis is in progress.

Similar to the procedures of assimilating all-sky AMSU-A radiances in the GSI-based hybrid data assimilation system, developments, such as in observation error model and quality control, are currently being made to assimilate all-sky radiances from the NASA Global Precipitation Measurement Mission (GPM) Microwave Imager (GMI). The Hurricane Weather Research and Forecasting (HWRF) model is adopted in numerical simulations of Hurricane Florence (2018) to examine the impacts of assimilating all-sky GMI radiances on track and intensity predictions.