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Jeudi 29 mars - Regional numerical modeling in the Tropical Atlantic: 1) variability of the mesoscale eddies in the Caribbean Sea, 2) impact of the intraseasonal waves on surface cooling in the Gulf of Guinea

Par semsou — Dernière modification 19/03/2012 11:00
Quand ? Le 29/03/2012,
de 11:00 à 12:30
Où ? salle Jules Verne
Participants Julien JOUANNO (CICESE Ensenada, Mexique)
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Julien JOUANNO (CICESE Ensenada, Mexique)

 

Regional numerical modeling in the Tropical Atlantic: 1) variability of the mesoscale eddies in the Caribbean Sea, 2) impact of the intraseasonal waves on surface cooling in the Gulf of Guinea

 

 

Résumé:

 

Regional numerical simulations are used to investigate two different aspects of the intraseasonal variability in the Tropical Atlantic Ocean :

1) Seasonal and interannual variability of the mesoscale eddy field in the Caribbean Sea during the period 1993-2009. It is shown that the Colombia Basin presents the largest values of Eddy Kinetic Energy (EKE) and its semi-annual cycle, with a main peak in August-October and a secondary peak in February-March, is the dominant feature in the whole Caribbean EKE cycle. The analysis of energy conversion terms between low-frequency currents and eddies explains these peaks by enhanced baroclinic and barotropic instabilities, in response to seasonally varying currents in the region of the Guajira Peninsula. The semi-annual acceleration of the atmospheric Caribbean Low Level Jet intensifies twice a year the southern Caribbean Current (sCC) in this region, together with its vertical and horizontal velocity shears.

2) Impact of the intraseasonal equatorial waves on the sea surface temperature fluctuations in the Gulf of Guinea. Results indicate that the seasonal cooling in this region is significantly shaped by short-duration cooling events caused by mixed Rossby-gravity waves within the 12-20-day period band, inertia-gravity waves with periods below 11 days and equatorially-trapped Kelvin waves with periods between 25 and 40 days. In these different ranges of frequencies, it is shown that the wave-induced horizontal oscillations of the northern front of the mean cold tongue dominate the variations of mixed-layer temperature near the equator. But the model mixed-layer heat budget also shows that the equatorial waves make a significant contribution to the mixed-layer heat budget through modulation of the turbulent cooling, especially above the core of the Equatorial Undercurrent (EUC). The mechanisms at play will be detailed.

 

 

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