Evidence of Loop Current Frontal Eddy Intensification Through Linear and Nonlinear Interactions with the Loop Current

During the 2010 Deepwater Horizon oil spill, an underestimated part of the oil was entrained into an intensified Loop Current Frontal Eddy (LCFE). These eddies, which are also known to play an important role in the Loop Current Eddy (LCE) shedding, are difficult to predict and the dynamics involving their intensification is still not fully understood. The Loop Current (LC) and its stronger LCFEs were continuously tracked during the 2009-2011 period using sea surface height (SSH) from AVISO+. A mooring array provided complementary information about the internal structure of the LC-LCFE interaction.

The intensification of the tracked LCFEs presented similar characteristics, independent of their location: a steep increase in kinetic energy, a corresponding decrease in SSH, and an increase in area. As the LCFE grows, the flow at the interface with the LC becomes stronger and deeper, and the horizontal density gradient between the features increases. The intensification of the front and the LCFEs is suggested to be driven by the advection (nonlinear) term, and the gradient pressure (linear) term of the Navier-Stokes equation. Evidence of an inverse energy cascade suggests that the LCFEs could be extracting energy and mass from the submesoscale, background field to the zone of contact between the LC and the LCFE, strengthening the front, and allowing the LCFEs to grow during periods of intensification. Understanding the physics driving the LCFE intensification is the first step to improving LC forecast models, and better predicting LCE shedding events and oil and particles transport around the LC.