The instabilities of the Antarctic slope current in an idealized model

Abstract

The Antarctic Slope Current (ASC), coupled with the Antarctic Slope Front (ASF), encircles Antarctica and is a roughly alongshore flow. Yet, the instabilities of the ASC/ASF can induce cross-slope exchanges. The ASC/ASF instabilities have been studied extensively in previous literature. However, the corresponding responsible mechanisms and influences still need to be further clarified. Based on an idealized eddy-resolving model, this study focuses on the instabilities of the ASC/ASF with constant open boundary forcing. The ASC/ASF is classified into three types: Fresh Shelf, Warm Shelf, and Dense Shelf. Focused on the Fresh Shelf and Dense Shelf cases, two high-resolution process-oriented numerical experiments are conducted to reveal the typical characteristics, the dynamic mechanisms, and the influences of instabilities. In the Fresh Shelf case, the instabilities are characterized by a submesoscale vortex train over the middle-lower slope, associated with the Topographic Rossby waves. In the Dense Shelf case, a mesoscale vortex train is present over the lower slope, and abundant filaments and jets can flow across the shelf break. The baroclinic instability greatly contributes to the generation of instabilities in the two cases, yet the barotropic instability contributes less to the instabilities in the Fresh Shelf case. Coherent eddies have been identified and significantly favor the hydrographic anomalies by the advection of water boluses retaining source water rather than the polarities of coherent eddies. Instabilities only contribute to exchanges across the continental rise in the Fresh Shelf case but effectively result in cross-slope exchanges in the Dense Shelf case.