Distribution of mesopelagic cephalopods around a warm–core ring in the East Australian Current (abstract)

A comparison is made of results for barotropic, surface and abyssal flows during the formation and passage of a warm-core ring in the East Australian Current. The barotropic velocities are estimated from sea-floor measurements of the horizontal electric field, which is induced by water motion. Values for the surface and near-bottom velocities are obtained generally by more traditional methods. A strong similarity is observed between the directions of the barotropic and surface flows. At a site close to the foot of the continental slope, the barotropic and near-bottom velocities are also similar, both in direction and magnitude. A possible explanation for this effect is that proximity to the coast constrains flow directions and causes the streamlines at depth to converge on the western (or near-shore) side of the warm-core ring. The determination of barotropic velocities enables barotropic volume transports to be estimated and compared with traditional geostrophic volume transports calculated for water motion between the surface and a depth of 1300 m. The barotropic transports are found to be greater than the geostrophic transports by a factor of approximately 1.6, indicating the significance of deep-water flow in the East Australian Current.

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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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