Benjamin Jaimes, Valerie Garnier, Laurent Cherubin, and Eric Chassignet, RSMAS/Univ. of Miami
The mean circulation of the Gulf of Mexico averaged over 6 Loop Current cycles is studied from a high resolution numerical simulation of the North Atlantic. The surface circulation pattern (first 500 m) is similar to observations, and consists of a global anticyclonic circulation composed of the anticyclonic loop of the Loop Current, the anticyclonic gyre to the west of the gulf, and the cyclonic gyre in the Campeche Bay. Deeper, the MICOM simulation circulation remains globally anticyclonic until 2000 m, while observations, and POM simulation, in particular, exhibit a cyclonic flow hugging the gulf shelf from 500 m until the bottom. Both observations and models finally agree on the cyclonic circulation below 2500 m. Following the hypothesis of Oey and Lee [2002] and DeHaan and Sturges [2004], which explain the cyclonic flow, in part by the rectification process induced by topographic rossby waves (TRWs), we study both the eddy kinetic energy (EKE) and potential energy divergence (POTD) vertical distribution in the MICOM simulation. EKE is ubiquitous in the entire gulf except below 2000 m along the shelf, while POTD forms a belt there. In the bottom layer, POTD exhibits a wave radiation pattern suggesting TWRs propagation across the Gulf of Mexico in MICOM bottom waters.
TWRs generation and propagation is then studied through the interaction of a shielded vortex and a bottom slope using a coarse and a fine vertical grid resolution in the MICOM model. While the fine grid resolution shows an even distribution of the velocities toward shallow layers, the coarse grid simulation shows bottom trapping of the wave energy. As the westward propagating waves also generate a westward flow, one can conclude that part of the cyclonic circulation is driven by TRWs, a product of the interaction of the Loop Current cyclonic satellites and the bottom topography. The MICOM coarse resolution simulation in the Gulf of Mexico prevents upward wave energy transfer that would drive a cyclonic flow in shallower layers.