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Alexis Lugo-Fernández
and
Robert R. Leben

Abstract

A linear correlation exists between the retreat latitude of the Loop Current following eddy separation and the subsequent eddy separation period. This empirical relationship was first identified in satellite altimeter-derived Loop Current metrics. In this paper, a simple vorticity model of the Loop Current is used to provide a semitheoretical basis for this relationship. After suitable scaling approximations, the theory predicts that the LC separation period is a linear function of retreat latitude, which agrees well with altimeter-derived empirical results. Specifically, the predicted slope and y intercept agree to within 9% and 2%, respectively, with the altimetry-derived values.

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Brian S. Powell
and
Robert R. Leben

Abstract

An optimal difference operator is derived for smoothing along-track sea surface height measurements from satellite altimeters and computing geostrophic surface currents at or below ocean mesoscale wavelengths with second-order approximation accuracy. The difference operator minimizes the white noise of the height measurements to find a compact difference formula for the sea surface height derivative and a residual noise estimate for the surface geostrophic velocity. This compact, optimal operator has fine along-track spatial resolution ideal for studies in areas of shallow water, near landfall, and at high latitudes where the first-baroclinic Rossby radius of deformation becomes small. Accurate extraequatorial geostrophic velocities are determined by varying the filter window to maintain accuracy and resolution, which will benefit global mesoscale studies from the tandem Jason-1 and TOPEX/Poseidon missions and, particularly, the proposed wide-swath altimetry mission.

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Wilton Sturges
,
Nicholas G. Hoffmann
, and
Robert R. Leben

Abstract

The Loop Current in the Gulf of Mexico sheds large anticyclonic rings on an irregular basis. The authors attempt to show what actually triggers the ring separations. Pulses of increased transport through the Florida Straits, as observed by the cable data, are observed prior to each ring separation. This finding is consistent over all separation events observed in the satellite altimetry record. The pulses of transport occur approximately two to four weeks before the rings separate. The increase in transport is usually accompanied by a corresponding increase in offshore sea level, suggesting forcing from the open ocean. The delay times between the pulses of increased transport and ring separations can be shown to be significantly correlated with the length of the Loop Current. Mean sea levels over the Caribbean and Gulf also peak before the separations, on average.

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Haosheng Huang
,
Nan D. Walker
,
Ya Hsueh
,
Yi Chao
, and
Robert R. Leben

Abstract

The Loop Current frontal eddies (LCFEs) refer to cyclonic cold eddies moving downstream along the outside edge of the Loop Current in the eastern Gulf of Mexico. They have been observed by in situ measurements and satellite imagery, mostly downstream of the Campeche Bank continental shelf. Their evolution, simulated by a primitive equation ⅙° and 37-level Atlantic Ocean general circulation numerical model, is described in detail in this study. Some of the simulated LCFEs arise, with the passage through the Yucatan Channel of a Caribbean anticyclonic eddy, as weak cyclones with diameters less than 100 km near the Yucatan Channel. They then grow to fully developed eddies with diameters on the order of 150–200 km while moving along the Loop Current edge. Modeled LCFEs have a very coherent vertical structure with isotherm doming seen from 50- to ~1000-m depth. The Caribbean anticyclone and LCFE are two predominant features in this numerical model simulation, which account for 22% and 10%, respectively, of the short-term (period less than 100 days) temperature variance at 104.5 m in the complex empirical orthogonal function (CEOF) analysis. The source water inside the LCFEs that are generated by Caribbean anticyclonic eddy impingement can be traced back, using a backward-in-time Lagrangian particle-tracking method, to the western edge of the Caribbean Current in the northwest Caribbean Sea and to coastal waters near the northern Yucatan Peninsula. The model results indicating a pairing of anticyclonic and cyclonic eddies within and north of the Yucatan Channel are supported by satellite altimetry measurements during February 2002 when several altimeters were operational.

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