Meeting Documents

Sub-mesoscale Wind-Front Interactions and Their Impact on Ocean Vertical Velocities

Abstract

Interactions between coherent meso- and sub-mesoscale surface ocean temperature and velocity structures induce wind stress anomalies. These anomalies impact air-sea exchange of momentum and may induce vertical velocities as a result of Ekman dynamics. The impact of these wind-front interactions, known as thermal (TFB) and current (CFB) feedbacks, have been studied extensively at mesoscale, using either satellite products or regional simulations. However, consideration of both feedbacks in tandem has been rare, and assessment of their joint impacts on sub-mesoscale vertical velocities remains immature.

Here, we apply a novel 2-D approach that simultaneously assesses TFB and CFB's joint influence and their relative importance on generating wind stress derivative anomalies. In particular, this study focuses on how wind-front feedbacks at sub-mesoscale modify ocean surface vertical velocities. We conduct regional analyses of the Southern Ocean and the California Current System with output from a 4-km sub-mesoscale-resolving global coupled simulation. A series of 2-D conditional mean plots map the distribution of wind stress curl or divergence with both CFB and TFB as axes. The synergy of TFB and CFB improves the ability to reconstruct the magnitude and spatial variations of wind stress curl from both surface vorticity and temperature gradients. We find that jointly-generated wind stress curl anomalies are enhanced at sub-mesoscale, especially in the Southern Ocean, with magnitudes that approach 10^-5 N m^-3, roughly 20 times stronger than at mesoscale. These wind stress curl anomalies have been shown to impact surface Ekman pumping, primarily through the non-linear component, and contribute to vertical velocity changes at fronts and filamentary regions. The study will also assess the relative importance of wind-front interactions on the near surface vertical transport of tracers in the ocean surface boundary layer.