Weather forecasting applications using WindSat

First, this paper illustrates potential use of WindSat wind vectors by forecasters using case studies. Second, we perform a statistical analysis with the eventual goal of data assimilation into U.S. Navy numerical models.

In case study mode, we show that WindSat vectors successfully delineate topographically-induced wind regimes, including gap winds and sheltered regions. Examples will be given for the vicinities of Japan, France, Sri Lanka, and Alaska. We will compare these examples to nearly coincident examples from the QuikScat Scatterometer and, when available, to forecast system output. The wind speeds in these regimes often fall within the range of 5 to 20 m/sec and are accurately resolved by the retrievals in most cases.

For purposes of eventual data assimilation, WindSat and QuikSCAT observations will be compared against the NRL Monterey Atmospheric Variational Data Assimilation System (NAVDAS) 10m wind analyses for October 2003-February 2004. For WindSat, we only examined observations for which the wind speed was less than or equal to 20 m/sec and WindSat quality control flags indicated the highest quality wind speed retrievals. For QuikSCAT, we only examined observations for which the wind speed was less than or equal to 20 m/sec. To ensure the highest data quality we considered only retrievals derived from the “sweet” part of the swath that was not rain contaminated. Statistics were computed for the differences between the observed and analysis wind directions and wind speeds for WindSat and QuikSCAT and were stratified by NAVDAS analysis wind speed. We computed global statistics for the entire 5-month period as well as for October, December, and February.

Our results suggest that WindSat performs well at all wind speeds considered, usually comparable to QuikSCAT. Directional differences with NOGAPS are about 10 degrees at high speeds (12.5 – 20 m/s), and between 20 – 30 degrees at 5 m/s or less. The relatively low directional differences at low speeds alleviate previous concerns about the performance of the instrument in light winds.