Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 1797–1806, doi:10.1002/jgrc.20141.
Layering of ocean velocity “fine structure” has been coherently observed across the entire extent of a Gulf Stream warm-core ring using a shipboard acoustic Doppler current profiler system in September 2009 and independently sampled as the ring transited a moored array. Lines of constant velocity phase generally followed isopycnals as they deepened within the ring center. We also observed a clear separation of the vertical structure of the flows associated with the ring (of order 0.5 m/s) with the shorter (200 m) and less energetic (~0.2 m/s) flows of the velocity fine structure, which was further observed to rotate clockwise with increasing depth, consistent with downward propagating near-inertial waves (NIWs). Observations are consistent with a ring-scale NIW packet, probably wind forced, that shows enhanced NIW energy within the sloping pycnocline at depths of 300–700 m. Evidence of wind-forced NIWs within anticylonic eddies in a numerical simulation shows some similar features to our observations, which we try to understand physically with basic WKB-type wave/current dynamics along the lines of previously published work and a new calculation of NIW trapping within an isolated, baroclinic vortex.
Initial observations at Station W (2001–2004)
were made possible by a grant from the G. Unger Vetlesen Foundation and
support from theWoods Hole Oceanographic Institution. Since 2004, the Line
W program (http://www.whoi.edu/science/PO/linew/) has been supported by
the U.S. National Science Foundation with supplemental contribution from
WHOI’s Ocean and Climate Change Institute. PK is supported by IFREMER and CNRS
Velocity fine structure
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