The synoptic sound-speed field of a warm-core gulf stream ring

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A synoptic expendable bathythermograph survey of the warm-core Gulf Stream ring 81-D, conducted in September 1981 when the ring was located 550 km south of Halifax, Nova Scotia, provided the basis for a detailed study of the ring’s sound-speed field. Salinities used for computing sound speed were derived from nonsynoptic conductivity-temperature-depth data collected during the survey. Analysis of the sound-speed field, using vertical and horizontal sections and satellite imagery, revealed the ring’s typical high sound-speed core, but also showed increased horizontal and vertical gradients along the ring’s western margin as compared to its eastern side. This asymmetry appears to be related to a surface streamer of warm, higher sound-speed Gulf Stream water overlying colder, lower sound-speed slope water, resulting in a subsurface sound duct centered 100 m below the surface along the ring’s western margin. The subsurface duct and increased vertical gradient resulted in 30–50 dB greater loss at depths of 100 and 200 m in the ring’s eastern margin as compared to its western side and center. Strong ray channeling and refraction of a 2000-Hz source at a depth of 100 m was also noted. Based on these observations and predictions, warm-core rings may possess regions of increased acoustic range dependence due to the interactions of waters along their margins. © 1984, Acoustical Society of America. All rights reserved.

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Journal of the Acoustical Society of America