On the Evolution of the Gulf of Mexico Loop Current Through Its Penetrative, Ring Shedding and Retracted States

Abstract

How the Gulf of Mexico Loop Current (LC) transitions from penetrative to ring shedding to retracted configurations remains an active research topic. Satellite altimetry suggests a set of states, some more persistent than others, identified as Campeche Bank Anchoring, West Florida Shelf Anchoring, Extended, and LC Ring, plus transitional phases. Histograms show that the most frequent states are Campeche Bank Anchoring and West Florida Shelf Anchoring. Two canonical evolutions are defined. The first is a transition from Campeche Bank Anchoring to West Florida Shelf Anchoring. The second is a transition from Campeche Bank Anchoring to Extended to LC Ring. Common to both are cyclonic eddies. The first canonical transition requires cyclones formed both east and west of the LC, acting as pincers far enough south to dislodge the LC from the Campeche Bank. The second has a single cyclone, formed on either side of the LC, that cuts through either from the east, thereby not dislodging the LC from the Campeche Bank, or from the west, but too far north to dislodge the LC. Notable is the importance of the Campeche Bank and Florida escarpments. Cyclones may generate either by instability or downslope perturbation, but whether these lead to protracted penetration, or just jostling from one anchoring state to another, depends on where they are generated and how they combine to shed a LC Ring. Thus, these findings suggest that furthering understanding and prediction requires observations and analyses over the two escarpment regions and the LC domain south of about 25°N.