Deriving CYGNSS Vector Winds and Their Impact on Regional Analyses of Tropical Cyclones in HWRF

Wind speeds retrieved from the CYclone Global Navigation Satellite System (CYGNSS) constellation are providing improved global spatial and temporal coverage of tropical ocean surface compared to polar orbiting microwave instruments (passive and active) that also produce estimates of wind speed or wind vectors. This study examines the analysis impacts of the increased sampling of CYGNSS compared to ASCAT, via assimilation of both CYGNSS retrieved wind speed and derived CYGNSS wind vectors in the operational Hurricane Weather Research and Forecast (HWRF) model. Because ASCAT vector winds are already a successful component of the operational analysis of tropical cyclones in HWRF and in data assimilation systems of other operational numerical weather prediction models (e.g., GFS, ECMWF), they provide an excellent baseline target for CYGNSS impact assessment.

CYGNSS vector winds in this study are derived via the 2-dimensional Variational Analysis Method (VAM) of Hoffman et al. (2003). The VAM methodology will be reviewed and analysis sensitivity studies on regional scales appropriate for the operational HWRF will be shown. Also, the comparative impacts of ASCAT and CYGNSS vector winds and wind speeds on HWRF analyses will be shown for one or more case studies of tropical Atlantic hurricanes via Observing System Experiments (OSEs). Finally, the combined effect of ASCAT and derived CYGNSS vector winds on the analyses of tropical cyclones will also be shown.