Symmetric instability under inertially resonant winds

ID：1345 Oral Presentation

2025-01-16 15:50 （China Standard Time）

Session：Session 46-Oceanic Mesoscale and Submesoscale Processes: Characteristics, Dynamics & Parameterizations

Abstract

When wind aligns with the geostrophic flow in the upper ocean (down-front wind), it induces a negative Ertel potential vorticity (EPV) flux, initiating symmetric instability (SI) along the frontal boundary. However, surface mixed layers (SMLs) are usually subjected to fluctuating wind forcing rather than a constant, unidirectional one. Notably, near-inertial wind components can inject significant kinetic energy into the upper ocean, forming strong near-inertial oscillations. These variations in wind forcing, along with the associated near-inertial oscillations, introduce additional complexities to the energy budget of the SML. In this study, we investigate the frontal SI dynamics using large-eddy simulations with a series of wind conditions. A refined dynamical decomposition method is developed to achieve a more refined analysis of interaction between different motions. Using this method, we demonstrate that available potential energy (APE) also plays a crucial role in energizing SI. Furthermore, periodic winds enhance near-inertial motions within the system thereby rendering ageostrophic shear production (AGSP) a progressively dominant mechanism in the energy transfer process. Ultimately, our refined decomposition framework enables a detailed assessment of the feedback exerted by SI on the broader system dynamics.