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A recently developed tool, the multiscale window transform, along with the theory of canonical energy transfer is used to investigate the roles of multiscale interactions and instabilities in the Gulf of Mexico Loop Current (LC) eddy shedding. A three-scale energetics framework is employed, in which the LC system is reconstructed onto a background flow window, a mesoscale eddy window, and a high-frequency eddy window. The canonical energy transfer between the background flow and the mesoscale windows plays an important role in LC eddy shedding. Barotropic instability contributes to the generation/intensification of the mesoscale eddies over the eastern continental slope of the Campeche Bank. Baroclinic instability favors the growth of the mesoscale eddies that propagate downstream to the northeastern portion of the well-extended LC, eventually causing the shedding by cutting through the neck of the LC. These upper-layer mesoscale eddies lose their kinetic energy back to the background LC through inverse cascade processes in the neck region. The deep eddies obtain energy primarily from the upper layer through vertical pressure work and secondarily from baroclinic instability in the deep layer. In contrast, the canonical energy transfer between the mesoscale and the high-frequency frontal eddy windows accounts for only a small fraction in the mesoscale eddy energy balance, and this generally acts as a damping mechanism for the mesoscale eddies. A budget analysis reveals that the mesoscale eddy energy gained through the instabilities is balanced by horizontal advection, pressure work, and dissipation. [ABSTRACT FROM AUTHOR]

Three simulations of the circulation in the Gulf of Mexico (the "Gulf") using different numerical general circulation models are compared with results of recent large-scale observational campaigns conducted throughout the deep (>1500 m) Gulf. Analyses of these observations have provided new understanding of large-scale mean circulation features and variability throughout the deep Gulf. Important features include cyclonic flow along the continental slope, deep cyclonic circulation in the western Gulf, a counterrotating pair of cells under the Loop Current region, and a cyclonic cell to the south of this pair. These dominant circulation features are represented in each of the ocean model simulations, although with some obvious differences. A striking difference between all the models and the observations is that the simulated deep eddy kinetic energy under the Loop Current region is generally less than one-half of that computed from observations. A multidecadal integration of one of these numerical simulations is used to evaluate the uncertainty of estimates of velocity statistics in the deep Gulf computed from limited-length (4 years) observational or model records. This analysis shows that the main deep circulation features identified from the observational studies appear to be robust and are not substantially impacted by variability on time scales longer than the observational records. Differences in strengths and structures of the circulation features are identified, however, and quantified through standard error analysis of the statistical estimates using the model solutions. [ABSTRACT FROM AUTHOR]

Subsurface jets, defined as having velocity maxima >40 cm s-1 at depths between 100 and 350 m, and being surrounded by much weaker near-surface currents, have been observed over the northwestern Gulf of Mexico continental slope. The observations were from an array of 14 moorings equipped with upward-looking 75-kHz ADCPs deployed at 450–500 m. A total of 10 jet events were observed in 18 ADCP years of velocity profile data, where these events were clearly not the result of downward-propagating inertial internal waves. The jets had durations from about 1 to 8 days and were usually associated with interactions between similarly sized cyclones and anticyclones over the slope or with the interaction of an eddy with upper-slope topography. The jets are associated with potential vorticity anomalies and their inferred length scales indicate that the dynamics depart from simple geostrophic balances. Observed anomalous density gradients present during the jets seem to involve the tilting of the vertical axis of the center of rotation of one or more of the interacting eddies. [ABSTRACT FROM AUTHOR]