Assimilation of ISS-RapidScat Ocean Surface Winds within NOAA Global Assimilation System

ISS-RapidScat is an International Space Station borne scatterometer launched by NASA in 2014. The retrieved Level-2B ISS-RapidScat ocean wind vector data are analyzed via the Community Observation Assessment Tool (COAT). The comparison of wind speed and direction with ECMWF model forecast shows general agreement, except the relatively large discrepancy in the wind direction (i.e., over 45 degree) over the regions with less than 5 m/s wind speed (e.g., northeastern Pacific). Quality control has been applied to remove rain contamination of RapidScat data. Further quality control has been done to filter out the low wind speed vectors, with which wind directions have large discrepancy in the data.

With the knowledge gained by assessing the surface wind data, RapidScat data have been properly formatted and ingested into NOAA Global Assimilation System, i.e., the 3-D hybrid ensemble variational GSI. The statistics of O-B and O-A in GSI for RapidScat wind speed and direction, wind u and v are analyzed. Innovated quality control in GSI is developed for RapidScat wind based on the pre-assimilation assessment.

Penalty as a function of model iterations has been shown for multiple observation errors in order to optimize the convergence during minimization. The impact of RapidScat wind in GSI analysis is independently assessed by comparing with ECMWF analysis. Finally, the impact of RapidScat wind in the forecast model is analyzed with the Verification Statistics Data Base (VSDB).