Measured changes in ocean surface roughness due to atmospheric boundary layer rolls

Type Article
Date 2001-03
Language English
Author(s) Vandemark D, Mourad Pd, Bailey Sa, Crawford Tl, Vogel Camille, Sun J, Chapron Bertrand
Affiliation(s) NASA, Goddard Space Flight Ctr, Lab Hydrospher Proc, Wallops Island, VA 23337 USA.
Univ Washington, Coll Ocean & Fishery Sci, Appl Phys Lab, Seattle, WA 98105 USA.
NOAA, Appl Res Lab, Field Res Div, Idaho Falls, ID 83402 USA.
NOAA, Atmospher Turbulence & Diffus Div, Oak Ridge, TN USA.
Natl Ctr Atmospher Res, Boulder, CO 80307 USA.
Inst Francais Rech Exploitat Mer, Ctr Brest, F-29280 Plouzane, France.
Source Journal Of Geophysical Research Oceans (0148-0227) (Amer Geophysical Union), 2001-03 , Vol. 106 , N. C3 , P. 4639-4654
WOS© Times Cited 19
Abstract A research aircraft was recently flown over the Mid-Atlantic Eight during a mild cold air outbreak to sample the planetary boundary layer at low levels of 15-20 m above the sea surface. Aircraft sensors measured near-surface atmospheric turbulence and, at the same time, variations in sea surface roughness using laser and radar. The aircraft turbulence observations indicate a coherent secondary flow consistent with boundary layer roll vortices of crosswind scale 1.5-2.0 km. Modulation in measured laser and radar-inferred sea surface slope variance occurs at similar scales. Remarkable correlation is found between the radar backscatter and near-surface wind speed data, showing that the short wave slope variance is responsive to these large eddies. Associated small but periodic changes in wind direction do not appear to impact the short wave slope signature. Differentiation between short- and intermediate-scale wave roughness using aircraft laser and radar data leads us to conclude that observed fluctuations in intermediate-scale wave slope were not directly linked to the local wind. A synthetic aperture radar (SAR) image was acquired by the Canadian Space Agency's RADARSAT coincident with the aircraft measurements. Widespread streaking in the SAR image suggests the surface impacts of atmospheric longitudinal rolls. Our aircraft results indicate that the dominant term dictating SAR backscatter modulations at the eddy scale of 1-2 km is the fluctuation of the along-wind velocity, nominally associated with regions of near-surface convergence or divergence. Wind speed fluctuations of 7-10% estimated from the SAR and aircraft radar are consistent with the aircraft's measured variations in near-surface wind speed.
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Vandemark D, Mourad Pd, Bailey Sa, Crawford Tl, Vogel Camille, Sun J, Chapron Bertrand (2001). Measured changes in ocean surface roughness due to atmospheric boundary layer rolls. Journal Of Geophysical Research Oceans, 106(C3), 4639-4654. Open Access version : https://archimer.ifremer.fr/doc/00000/10364/