Modeling and observation of low-frequency propagation into warm core ring on the New England shelf slope

A warm core ring and adjacent waters off the Scotian Shelf in June 1982 contained substantial numbers of larval and juvenile white hake, Urophycis tenuis, as far as 140 km seaward of the continental shelf break. The warm core ring, designated 81-G, had entrained shelf water on several occasions before the shipboard observations were made. We suggest that the ring contributed to the offshore advection of these fish, which probably were spawned on the continental shelf or upper slope. Warm core rings can disrupt the usual larval drift pattern of shelf–slope fishes and thereby affect recruitment. Larvae and juveniles of several species of tropical–subtropical fishes found in ring 81-G have been reported previously as rare specimens in ichthyoplankton surveys on the Scotian Shelf. Our observations support the hypothesis that warm core rings can be a mechanism for transport of these expatriated fishes onto the shelf.

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The Dynamical Structure of a Warm Core Ring as Inferred from Glider Observations and Along-Track Altimetry

Remote Sensing ◽

10.3390/rs13132456 ◽

2021 ◽

Vol 13 (13) ◽

pp. 2456

Author(s):

Thomas Meunier ◽

Enric Pallás Sanz ◽

Charly de Marez ◽

Juan Pérez ◽

Miguel Tenreiro ◽

...

Keyword(s):

Rotation Axis ◽

Relative Vorticity ◽

Dynamical Structure ◽

Loop Current ◽

Energy Partition ◽

Warm Core ◽

Warm Core Ring ◽

Current Ring ◽

Along Track ◽

Pv Gradient

This study investigates the vertical structure of the dynamical properties of a warm-core ring in the Gulf of Mexico (Loop Current ring) using glider observations. We introduce a new method to correct the glider’s along-track coordinate, which is, in general, biased by the unsteady relative movements of the glider and the eddy, yielding large errors on horizontal derivatives. Here, we take advantage of the synopticity of satellite along-track altimetry to apply corrections on the glider’s position by matching in situ steric height with satellite-measured sea surface height. This relocation method allows recovering the eddy’s azimuthal symmetry, precisely estimating the rotation axis position, and computing reliable horizontal derivatives. It is shown to be particularly appropriate to compute the eddy’s cyclo-geostrophic velocity, relative vorticity, and shear strain, which are otherwise out of reach when using the glider’s raw traveled distance as a horizontal coordinate. The Ertel potential vorticity (PV) structure of the warm core ring is studied in details, and we show that the PV anomaly is entirely controlled by vortex stretching. Sign reversal of the PV gradient across the water column suggests that the ring might be baroclinically unstable. The PV gradient is also largely controlled by gradients of the vortex stretching term. We also show that the ring’s total energy partition is strongly skewed, with available potential energy being 3 times larger than kinetic energy. The possible impact of this energy partition on the Loop Current rings longevity is also discussed.

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