THE SEMIANNUAL OSCILLATION AND ANTARCTIC CLIMATE - PART-2 - RECENT CHANGES

Following a weakening of the semi-annual oscillation (SAO) since the m id-1970s, the half-yearly pressure wave in the Southern Hemisphere has become less significant. As a result, May/June temperatures have decr eased in East Antarctica, which has moderated Antarctic warming. Spect ral analysis of 87 years of pressure data at Orcadas suggest that the recent weakening of the SAO is part of the natural variability of the Southern Hemisphere circulation on decadal timescales. We interpret th e time series of composite Antarctic temperature in terms of the histo rical strengthening and weakening of the SAG. If the dominant oscillat ions that occurred in the past prove to be persistent, an accelerated East Antarctic warming trend is expected for the coming decades. There are indications that the strength of the SAO is linked to the Souther n Oscillation, in the sense that warm phases of the Southern Oscillati on coincide with strong westerlies, a weakly developed SAO and below-a verage temperatures in East Antarctica. Temperatures on the west coast of the Antarctic Peninsula show strongly deviant patterns, which can not be explained by the same mechanism that applies to East Antarctica .