Properties of the Subantarctic Front and Polar Front from the skewness of sea level anomaly

Andrew E Shao,Luanne Thompson,Sabine Mecking,Sarah T Gille

doi:10.1002/2015jc010723

Abstract

The region of the Southern Ocean that encompasses the Subantarctic Front (SAF) to the north and the Polar Front (PF) to the south contains most of the transport of the Antarctic Circumpolar Current. Here skewness of sea level anomaly (SLA) from 1992 to 2013 is coupled with a meandering Gaussian jetw model to estimate the mean position, meridional width, and the percent variance that each front contributes to total SLA variability. The SAF and PF have comparable widths (85 km) in the circumpolar average, but their widths differ significantly in the East Pacific Basin (85 and 60 km, respectively). Interannual variability in the positions of the SAF and PF are also estimated using annual subsets of the SLA data from 1993 to 2012. The PF position has enhanced variability near strong topographic features such as the Kerguelen Plateau, the Campbell Plateau east of New Zealand, and downstream of Drake Passage. Neither the SAF nor the PF showed a robust meridional trend over the 20 year period. The Southern Annular Mode was significantly correlated with basin-averaged SAF and PF positions in the East Pacific and with the PF south of Australia. A correlation between the PF and the basin-scale wind stress curl anomaly was also found in the western extratropical Pacific but not in other basins.

Highlights

The Antarctic Circumpolar Current (ACC) is the one of the most dominant, dynamical features in the Southern Ocean
We used a Monte-Carlo simulation based on a meandering Gaussian jet model to demonstrate that a jet’s width and SNR modulate the skewness signature first explored by TD06
Unlike many other frontal detection schemes, no estimates of mean dynamic topography (MDT) are required, ensuring that any temporal variability in frontal location is unaffected by large-scale sea surface height (SSH) changes

Summary

Introduction

The Antarctic Circumpolar Current (ACC) is the one of the most dominant, dynamical features in the Southern Ocean. Much of the large-scale, eastward flow organizes into jets in three distinct regions (from north to south): the Subantarctic Front (SAF), the Polar Front (PF), and the Southern ACC Front (SACCF). Each of these fronts characterizes regions where near-surface hydrographic properties change rapidly. The fronts tend to be aligned zonally except in regions where steeply sloping topography steers their paths, for example south of New Zealand around the Campbell Plateau, Scotia Sea and in the Brazil Basin. These fronts are in geostrophic balance resulting in jets whose zonal velocities are described by g @g ug f @y ;

Methods

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Discussion

Conclusion