Surface wind response to oceanic fronts

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The response of surface winds to ocean fronts characterized by sharp gradients in both sea surface temperature (SST) and ocean currents was analyzed using scatterometer (NSCAT and QuikSCAT) wind data and Gulf Stream path positions in conjunction with simulations made with the Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5). All match-ups, between each scatterometer pass and the Gulf Stream path, were visually examined and only those for which the wind field was free of atmospheric fronts or large curvature over a reasonably straight segment of the Gulf Stream were selected. Ten match-ups met these criteria for the period studied from 16 September 1996 to 29 June 1997 for NSCAT and from 24 July 1999 to 31 December 2000 for QuikSCAT. Changes in the modeled surface wind field across the front in each of the ten cases agree well with changes in the observed winds. Our findings suggest that the perturbation pressure gradient resulting from the thermal forcing by the front accounts for the decrease in wind speed when moving from warm to cold water and the increase observed in the converse. In the cases examined, the adjustment of the surface wind to the front occurred as a result of the vertical motion induced by horizontal divergence/convergence and advection in the marine atmospheric boundary layer (MABL). The dynamical forcing associated with strong surface currents is also shown to modify scatterometer-derived winds. Finally the numerical simulations suggest that the dynamical and thermal effects are very nearly additive. Copyright 2006 by the American Geophysical Union.

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Journal of Geophysical Research: Oceans