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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, C03021, doi:10.1029/2005JC003016, 2006

Modification of surface winds near ocean fronts: Effects of Gulf Stream rings on scatterometer (QuikSCAT, NSCAT) wind observations

Kyung-Ae Park

Research Institute of Oceanography, Seoul National University, Seoul, Korea


Peter Cornillon

Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA


Daniel L. Codiga

Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA


Abstract

Modifications to surface winds by currents and sea surface temperature (SST) gradients near frontal boundaries of Gulf Stream rings are analyzed using satellite SST and scatterometer (NASA's Quick Scatterometer (QuikSCAT), NASA scatterometer (NSCAT)) wind observations. A component of scatterometer wind approximately equal and opposite to the surface current vector is observed and attributed to the fact that scatterometers detect relative motion of water and air. Warm-core ring (WCR) SSTs act to destabilize the marine atmospheric boundary layer (MABL), increasing surface wind magnitude by 10–15% and decreasing veering angle by 5–15° relative to large-scale mean winds. Cold-core ring (CCR) SSTs cause impacts of similar magnitude and opposite sense. Magnitudes and directions of modifications are accounted for by MABL dynamics of a nonlinear planetary boundary layer model forced by air-sea temperature differences. Wind modifications occur within tens of kilometers of SST fronts, implying a wind response timescale of order 1 hour. By contrast, uniformity of modified winds across the larger area within rings suggests the response time for the MABL to return to equilibrium downstream from a front exceeds 10 hours. Over WCRs, strong divergence (convergence) occurs on the upwind (downwind) side; curl is strongly negative (positive) to the right (left) side facing downwind. Opposite patterns are generally seen over CCRs. Divergence (curl) peaks where winds blow perpendicular (parallel) to SST fronts. SST image analysis indicates enhanced cloudiness occurs with downwind convergence over WCRs. Wind stress curl due to ring modifications causes dipolar Ekman pumping sufficient to influence ring translation and decay processes.

Received 21 April 2005; accepted 28 December 2005; published 30 March 2006.

Keywords: cloudiness; Gulf Stream rings; scatterometer winds.

Index Terms: 3339 Atmospheric Processes: Ocean/atmosphere interactions (0312, 4504); 3360 Atmospheric Processes: Remote sensing; 4520 Oceanography: Physical: Eddies and mesoscale processes; 4528 Oceanography: Physical: Fronts and jets; 3307 Atmospheric Processes: Boundary layer processes.

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Citation: Park, K.-A., P. Cornillon, and D. L. Codiga (2006), Modification of surface winds near ocean fronts: Effects of Gulf Stream rings on scatterometer (QuikSCAT, NSCAT) wind observations, J. Geophys. Res., 111, C03021, doi:10.1029/2005JC003016.