Abstract

In contrast to earlier studies, we describe the climatological deep low-pressure system that exists over the South Pacific sector of the Southern Ocean, referred to as the Amundsen Seas Low (ASL), in terms of its relative (rather than actual) central pressure by removing the background area-averaged mean sea level pressure (MSLP). In doing so, we remove much of the influence of large-scale variability across the ASL sector region (e.g., due to the Southern Annular Mode), allowing a clearer understanding of ASL variability and its effect on the regional climate of West Antarctica. Using ERA -Interim reanalysis fields the annual cycle of the relative central pressure of the ASL for the period 1979 to 2011 shows a minimum (maximum) during winter (summer), differing considerably from the earlier studies based on actual central pressure which suggests a semi-annual oscillation. The annual cycle of the longitudinal position of the ASL is insensitive to the background pressure, and shows it shifting westwards from 250° E to 220° E between summer and winter, in agreement with earlier studies. We demonstrate that ASL variability, and in particular its longitudinal position, plays an important role in controlling the surface climate of West Antarctica and the surrounding ocean by quantifying its influence on key meteorological parameters. Examination of the ASL annual cycle in seventeen CMIP5 climate models run with historical forcing showed that the majority of them have definite biases, especially in terms of longitudinal position, and a correspondingly poor representation of West Antarctic climate.

• Website for index: http://www.antarctica.ac.uk/data/absl/

• Publication: http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00813.1