The Global Distribution of the Time-Average Wind Stress Curl from NSCAT

Abstract

The time-average wind stress curl field for the global ocean is computed from the wind retrievals of the NASA Scatterometer (NSCAT) mission spanning the period 1 October 1996?29 June 1997. Particular attention is paid to large-amplitude, small-scale ?patchiness? in the average wind stress curl over the major ocean basins, and to long and narrow wind stress curl features that occur along ocean eastern boundary regions. The 9-month-average wind stress curl field from NSCAT is examined at 0.5°, 1°, and on a Gaussian grid consistent with T62 truncation in a spectral forecast model. The latter field is compared with the average wind stress curl field from NCEP analyses for the same period. Artifacts in the NCEP average overlap the regions of boundary wind stress curl extrema in the high-resolution averages from NSCAT. The artifacts are attributed to the effects of spectral truncation and tall near-coastal topography in the NCEP forecast model. Possible explanations are discussed for the boundary wind stress curl features that are most pronounced in the NSCAT data with 0.5° resolution. Patchiness in the average wind stress curl fields from NSCAT is considered in the context of aliases introduced by the complex spatiotemporal sampling pattern, and given the intermittency and large gradients that characterize the true wind stress curl field over the ocean. Implications from this rather detailed study of a single broad-swath, active scatterometer system are timely in light of recent plans for international cooperation in providing more than a decade of near-mesoscale resolution of the global surface vector wind field.