Establishing A Mapping Methodology For NSCAT Winds.
WASHINGTON UNIV SEATTLE APPLIED PHYSICS LAB
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A methodology is presented for mapping swath-oriented NASA scatterometer NSCAT wind data into gridded maps suitable for forcing ocean circulation models. NSCAT samples the winds over the equatorial Pacific Ocean unevenly in both space and time, and care must be taken in mapping them onto a grid to prevent aliasing the fields. It was necessary to develop a true wind field with which to test the mapping methodology. Prior to the availability of NSCAT data, the European Centre for Medium-Range Weather Forecasts ECMWF and Fleet Numerical Meteorology and Oceanography Center FNMOC analysis wind fields were studied. Spectral analysis of the ECMWF and FNMOC wind fields showed a drastic drop in energy at scales smaller than 600 km. These energy levels were pumped up in the Fourier domain to represent a true wind field more accurately. These true wind fields were converted to pseudostress, subsampled with the known NSCAT sampling pattern termed synthetic NSCAT winds, and then objectively averaged. A study of the expected errors of the mapped pseudo- stress was conducted using a convarience function of the equatorial Pacific wind field determined with data from the Tropical Atmosphere Ocean TAO buoy array. A 5-day, 20 resolution was chosen for the daily mapped pseudostress. Comparisons of the true winds converted to pseudostress and the mapped synthetic NSCAT pseudostress show errors consistent with the expected values. Maps made of actual NSCAT data are also presented and discussed.