Evidence of Loop Current Frontal Eddy intensification through local 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 essential role in the Loop Current eddy (LCE) shedding, are difficult to predict, and the dynamics involving their intensification are still not fully understood. The Loop Current (LC) and its strongest LCFEs were continuously tracked during 2009-2011 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 negative increase in SSH, and an increase in its 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 driven by the advection (nonlinear) term and the gradient pressure (linear) term in the momentum budget. Evidence of an inverse energy cascade suggests that LCFEs are extracting energy and mass from the submesoscale 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 a key step to improve LC forecast models and to better predict LCE shedding events, as well as oil and particle transport around the LC. Plain Language Summary Loop Current Frontal Eddies (LCFEs) are cool whirlpools located in the vicinity of the Loop Current (LC). These circulation features are known to play a crucial role in the separation of large warm whirlpools from the LC. Additionally, the LCFEs influence the local circulation. During the 2010 Deepwater Horizon oil spill, part of the oil was entrained around and inside an intensified LCFE, preventing it from reaching the Florida Keys as previously predicted by forecast models. Thus, understanding the LCFE intensification is a key step to improve LC forecast models and to better predict oil and particle transport around the LC. The LC and its strongest LCFEs were studied and continuously tracked using satellite and a mooring array for 2009-2011. During intensification periods, the LCFEs spin faster and become larger and deeper and the LC-LCFE front becomes stronger. Evidence shows that during intensification periods, the LCFEs entrain mass from the surrounding waters and store in its center, which explains the accumulation of the oil inside an intensified LCFE during the 2010 Deepwater Horizon oil spill.