THE SEMIANNUAL OSCILLATION AND ANTARCTIC CLIMATE - PART-1 - INFLUENCEON NEAR-SURFACE TEMPERATURES (1957-79)

We studied the influence of the semi-annual oscillation (SAO) on near- surface temperatures in Antarctica, using observations of 27 stations that were operational during (part of) the period 1957-79. For the ann ual cycle of surface pressure, the second harmonic explains 17-36% of the total variance on the Antarctic Plateau, 36-68% along the East Ant arctic coast and almost 80% on the west coast of the Peninsula, and de creases further to the north. As a result of the amplification of the wave-3 structure of the circulation around Antarctica, a significant m odification of the seasonal cooling is observed at many stations. The magnitude of this modification is largely determined by the strength o f the temperature inversion at the surface: the percentage of the vari ance explained by the second harmonic of the annual temperature cycle is then largest on the Antarctic Plateau (11-18%), followed by the lar ge ice shelves and coastal East Antarctica (6-12%) and stations at or close to the Peninsula (0-5%). A significant coupling between the half -yearly wave in surface pressure and that in surface temperature is fo und for coastal East Antarctica, which can be directly explained by th e changes in meridional circulation brought about by the SAG. We show that the coupling of Antarctic temperatures to the meridional circulat ion is not only valid on the seasonal time scale of the SAG, but proba bly also on daily and interannual time scales. This has important impl ications for the interpretation of time series of Antarctic temperatur es, a problem that will be addressed in part 2 of this paper.