Instabilities and Multiscale Interactions Underlying the Loop Current Eddy Shedding in the Gulf of Mexico

Abstract

A recently developed tool, the multiscale window transform, along with the theory of canonical energy transfer is used to investigate the roles of multiscale interactions and instabilities in the Gulf of Mexico Loop Current (LC) eddy shedding. A three-scale energetics framework is employed, in which the LC system is reconstructed onto a background flow window, a mesoscale eddy window, and a high-frequency eddy window. The canonical energy transfer between the background flow and the mesoscale windows plays an important role in LC eddy shedding. Barotropic instability contributes to the generation/intensification of the mesoscale eddies over the eastern continental slope of the Campeche Bank. Baroclinic instability favors the growth of the mesoscale eddies that propagate downstream to the northeastern portion of the well-extended LC, eventually causing the shedding by cutting through the neck of the LC. These upper-layer mesoscale eddies lose their kinetic energy back to the background LC through inverse cascade processes in the neck region. The deep eddies obtain energy primarily from the upper layer through vertical pressure work and secondarily from baroclinic instability in the deep layer. In contrast, the canonical energy transfer between the mesoscale and the high-frequency frontal eddy windows accounts for only a small fraction in the mesoscale eddy energy balance, and this generally acts as a damping mechanism for the mesoscale eddies. A budget analysis reveals that the mesoscale eddy energy gained through the instabilities is balanced by horizontal advection, pressure work, and dissipation.

Influence of Stratification and Yucatan Current Transport on the Loop Current Eddy Shedding Process

“…EAPE describes the temporary variations in MAPE, so zones with high EAPE identify the formation region and trajectories of the LCEs, consistent with energy transfer from EAPE to EKE due to baroclinic instability (Donohue et al, 2016;Yang et al, 2020). Zones with high EAPE are mostly located in the eastern GoM deeper than 1,000 m (Figure 3b), consistent with Yang et al (2020). The close relationship between the EAPE (Figure 3b) and EKE ( Figure 3d) patterns is noticeable (cf.…”

“…The result that 〈MAPE〉 dominates Bu e supports the idea that the dynamics of the LCS is highly related to the content of available potential energy. Nonetheless, it must be remembered that the LCS dynamics involves many different energy transfer processes spanning various temporal and spatial scales (Donohue et al., 2016; Maslo et al., 2020; Yang et al., 2020). Among all those processes, Yang et al.…”

Eddies connect the tropical Atlantic Ocean and the Gulf of Mexico

“…The eddy cases and the ADT propagation indicate that in contrast to the previous studies, mesoscale eddies from the tropical Atlantic Ocean, at least some of them, can cross the discontinuity regions and finally reach the GoM. These eddies serve as vorticity flux passing the Yucatan Channel and could trigger the Loop Current retraction, extension and eddy-shedding (e.g., Yang et al, 2020). Previous studies suggest that the negative (anticyclonic) vorticity flux is related to the Loop Current extension while the positive (cyclonic) vorticity flux causes retraction and sometimes shedding (e.g., Athié et al, 2012;Candela et al, 2002).…”

Eddies Connect the Tropical Atlantic Ocean and the Gulf of Mexico

“…Numerical modeling studies (e.g., Murphy et al., 1999) show that potential vorticity from NBC rings reforming west of the Lesser Antilles may then grow in the Caribbean Sea gaining energy via mixed barotropic and baroclinic instabilities. Some of those eddies can then enter the GoM through the Yucatan Channel, perhaps impacting the trajectory of the LC and the related eddy‐shedding process (e.g., Yang et al., 2020). Besides the modeling studies, drifter track, altimetry observations and Amazon river plume studies also show the advection of these eddies and its filaments cross the Lesser Antilles (e.g., Carton & Chao, 1999; Chérubin & Richardson, 2007; Fratantoni & Richardson, 2006; Goni & Johns, 2001; Richardson, 2005).…”