Jeudi 23 février - Meso and submesoscale dynamics in the Gulf of Mexico
de 11:00 à 12:00
|Où ?||Salle Lyot|
Julien Jouanno, LEGOS/IRD
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Titre : Meso- and submesoscale dynamics in the Gulf of Mexico
1) Loop Current Frontal Eddies: formation along the Campeche Bank and impact of coastally-trapped waves. Velocity data from a mooring array deployed northeast of the Campeche Bank (CB), shows the presence of subinertial high-frequency (below 15 days) velocity fluctuations within the core of the northward flowing Loop Current. These fluctuations are associated with the presence of surface intensified Loop Current Frontal Eddies (LCFEs), with cyclonic vorticity and diameter < 100 km. Analysis of high resolution simulations suggests that they originate along and north of the CB, their main energy source being the mixed baroclinic-barotropic instability of the northward flow along the shelf break. Model results show that wind variability associated with winter cold surges are responsible for the emergence of high-frequency LCFEs in a narrow band of periods (6-10-day) in the region of the CB.
2) Impact of submesoscale dynamics on vertical exchanges of tracers in the Gulf of Mexico. A set of long term regional simulations (with horizontal resolution at ¼°, 1/12° and 1/36°) has been designed to investigate the role played by the meso- and submesoscale turbulence on the dispersion of passive tracers in the upper layers of the Gulf of Mexico. In contrast to recent studies suggesting that enhanced submesoscale activity in the winter mixed layer may achieve efficient exchanges with the permanent thermocline below, the model analysis suggests that the eddy activity at scales shorter than the mesoscale reduces the exchanges between the surface and the thermocline. This effect is explained by the restratifying action of the submesoscale turbulence that efficiently limits the deepening of the mixed-layer in response to atmospheric winter synoptic events.