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On the Interaction Between the Mixed Layer and Deeper Ocean in The Gulf Stream Region

Yeon Chang, Jean Mensa, Zulema Garraffo, Tamay Ozgokmen
RSMAS, University of Miami
(Abstract received 05/14/2012 for session C)
ABSTRACT

The influence of coherent features on the exhange between the mixed layer and deeper ocean is investigated. To this end, we have chosen cyclonic and anticyclonic rings during both of the summer and winter seasons from the two HYCOM computations with submesoscale-resolving (1/48 degree) and only mesoscale-resolving 1/12 degree) resolutions near the Gulf Stream. In addition, regions with apparent mesoscale features have been considered for each season as well.

The result shows that, regardless of the strong personal characteristics of each ring, the vertical flow energy and the vertical particle dispersion rate are stronger in the winter for the deep ocean, although the horizontal flow energy are comparable for both cyclonic and anticyclonic rings in case of the high resolution. This is likely due to the strong stratification at the surface in summer, which suppresses the vertical mixing of the rings. In winter when the mixed layer is thicker and lots of submesoscale structures are active at the surface, the vertical momentum transfer is easier between the surface mixed layer and deeper ocean through the rings which may provide the ways of transfer through the density front made by the rings. For example, the vertical particle dispersion is much larger near the surface in the winter for both of the rings and even when there are no rings because of the strong energy of the submesoscales within the thicker mixed layer. In case there is no coherent features, however, the strong vertical dispersion rapidly decreases below the mixed layer. With the rings, the high dispersion rates extend through the water columns below the mixed layer. In the low resolution simulations, mixed layer instabilities and frontogenesis are not well resolved, and the seasonality of the exchange is not clear.