Modulation in interannual sea ice patterns in the Southern Ocean in association with large-scale atmospheric mode shift

Abstract

We verified that the synchronous propagations of the spatial patterns of sea ice concentration (SIC) of wave number 2 around the Antarctic occurred only for the period 1984 to 1994. An empirical orthogonal function (EOF) analysis of satellite data for 1979-2003 objectively demonstrates that the spatial pattern of SIC propagated eastward only in 1984-1994; in other years, it did not. Our results show that interannual variations in SIC patterns are associated with differences in the dominant large-scale atmospheric patterns. In nonpropagating years, variance of the tropospheric Antarctic oscillation (AAO) predominated. However, in propagating years, the AAO variance was subdominant to that of the Pacific South American (PSA) teleconnection pattern having a 4 year period. Such periodic PSA enables the SIC anomalies to propagate eastward with a periodically reinforced dipole pattern. The shift of large-scale atmospheric variability is one possible cause of the modulation in the SIC pattern. The switch of the atmospheric EOF leading mode from the PSA pattern to the AAO in the mid-1990s corresponded to the modulation in the SIC pattern and supports the presence of the atmospheric climate shifts. Copyright 2009 by the American Geophysical Union.