16th Conference on Air-Sea Interaction

P4.2

Satellite and in situ observations of marine boundary layer adjustment to an unstable-to-stable stratification transition

Ralph C. Foster, APL/Univ. of Washington, Seattle, WA; and D. Vandemark, H. Stern, L. Mahrt, D. Vickers, W. M. Drennan, D. G. Long, P. Vachon, and P. Mourad

We present a case study of marine boundary layer adjustment

to a sharp change in near-surface stratification from slightly

unstable to stable. The stratification change was induced by a sea

surface temperature front associated with the western edge of the Gulf

Stream at the edge of the continental shelf. This case is unique in

that a low flying research aircraft acquired near-surface flux and

surface wave information in coordination with a synthetic aperture

radar image acquisition from the Canadian Space Agency RADARSAT-1

satellite. Serendipitously, the NASA QuikSCAT scatterometer sampled

the same region within twelve minutes of the SAR image. Four issues of

scientific interest are revealed in this analysis. (1) We find clear

evidence of a near total collapse of the boundary layer at the leading

edge of the stably stratified region; (2) The near-surface winds at

the leading edge of the cooler sea surface appear to reduce below the

threshold necessary for inducing the cm-scale capillary/small gravity

waves that produce the Bragg scattering of the SAR microwave radar

beam; (3) The SAR wind retrievals and bulk flux model estimates of the

surface wind disagree with the in situ data in the stably stratified

region; (4) The low surface wind speeds in the stably-stratified

near-shore region allow the SAR image to resolve spiral eddies on the

sea surface, which provide a visualization of the ocean surface

vortices that are induced by horizontal shear instabilities in the

surface currents.

extended abstract  Extended Abstract (1.1M)

Poster Session 4, POSTERS: Small-Scale Studies
Wednesday, 14 January 2009, 2:30 PM-4:00 PM, Hall 5

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