Extended Abstract (1.1M)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.
Poster Session 4, POSTERS: Small-Scale Studies
Wednesday, 14 January 2009, 2:30 PM-4:00 PM, Hall 5
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