WindSat polarimetric microwave observations improve southern hemisphere numerical weather prediction

WindSat was launched in 2003 and is the first satellite-borne fully polarimetric microwave radiometer (Gaiser et al. 2004). This is an early report indicating the potential benefit of polarimetric microwave observations from this instrument. Initial studies examining the impact of WindSat polarimetric microwave observations when assimilated into a version of the National Centers for Environmental Prediction’s (NCEP) Operational Global Data Assimilation System have been completed. The studies were designed to quantify the utility of these data for operational numerical weather prediction (NWP). The initial studies involved the use of WindSat Version-2 wind vectors generated at the Naval Research Laboratory (NRL). The utility of the vectors has been assessed in terms of the assimilation methodology, data thinning, quality control and their benefit to the operational forecast system. Their impact has also been compared to that of data from the QuikSCAT polar-orbiting satellite. In these initial studies for the period 1 January to 15 February 2004, forecasts using the operational database (January 2004) plus WindSat wind vectors showed a modest positive impact compared to using only the operational database in forecasts out to five days. It should be noted however that the control in these studies used the full operational database including QuikSCAT data, which cover much of the area observed by WindSat for each analysis period. Over the southern hemisphere, for this study period, the impact of WindSat data in the operational database without QuikSCAT data was also recorded and shown to be of less benefit than that from the inclusion of QuikSCAT data in the operational database.