Meeting Documents

Response of Submesoscale Variability Under Sea Ice to Wind Bursts and Mesoscale Strain

Abstract

Submesoscale variability in the oceanic mixed layer under sea ice can be energetic in marginal ice zones, near large sea ice floes, near leads, or under packed winter sea ice, especially when horizontal density gradients are sufficiently strong to support the development of mixed layer instabilities. Previous studies have demonstrated that winter sea ice can provide a frictional dissipation mechanism that suppresses submesoscale eddies and dramatically reduces the associated eddy overturning streamfunction in the mixed layer, thus constraining the restratification of mixed layer fronts. While parameterization development commonly uses simulations with equilibrated, idealized frontal conditions, winter ice-ocean mixed layer dynamics are highly variable in space and time and subject to intermittent forcing. This study explores mechanisms driving transient submesoscale variability in a relatively high-resolution global ocean model, LLC4320, focusing on winter mixed layer dynamics in the Arctic Ocean. We identified mesoscale strain and wind bursts as critical factors affecting the strength of submeoscale eddies, in addition to the well-known influence of mixed layer depth and horizontal density gradients. During wind bursts, the vertical shear arising in response to the rapid motion of sea ice dramatically weakens existing submesoscale eddies. Shortly after the winds subside, submesoscale eddies regenerate with larger amplitude due to increased mixed layer depth from the wind-driven mixing. Frontogenesis can lead to enhanced submesoscale variability in regions of moderate mesoscale variability. However, despite facilitating frontal development, strong mesoscale eddies suppress submesoscale variability in the form of small-scale eddies, only allowing stable filamentary-type flows to develop at small scales. Our study highlights the complexity of interpreting under-ice submesoscale variability using conventional equilibrium frameworks and calls for the development and implementation of more advanced parameterizations that account for the role of wind bursts and mesoscale eddies.View Document (AGU) »