Cyclone--Anticyclone Asymmetry Organizes Local Energy Transfers during Mixed Layer Instability

Bing Han, Xiaolei Li, Lingling Xie, yang zhang 

Mixed layer instability (MLI) generates submesoscale fronts, filaments, and eddies, yet how cyclone--anticyclone asymmetry shapes the spatial distribution of energy transfers remains unclear. Ageostrophic convergence during frontal sharpening amplifies cyclonic vorticity, first producing a positively skewed vorticity distribution and later a cyclonically biased flow. We analyze a freely evolving idealized MITgcm front using horizontal coarse-graining and derive local budgets for resolved kinetic energy (KE) and eddy available potential energy (EAPE), retaining horizontal divergence, subfilter covariances, pressure-gradient work, vertical advection, and dissipation. The diagnosed flow exhibits a pronounced spatial asymmetry: convergent cyclonic cold filaments support forward KE and EAPE transfer, whereas divergent anticyclonic warm patches favor inverse transfer. Horizontal convergence and divergence also modulate other budget terms, including the isotropic cascade contributions, subfilter velocity--divergence and buoyancy--divergence couplings, and the local expansion or compression of resolved energy. These terms therefore inherit a cold--warm spatial organization from the cyclone--anticyclone pattern, while strain-dependent deviatoric transfer provides an additional pathway that can reinforce forward EAPE transfer under preferential cross-front compression. The results show that cyclone--anticyclone asymmetry spatially organizes both interscale cascades and other transfer terms in the local energy budgets.