Decadal and interannual variations in the Southern Hemisphere and sea surface temperature anomalies

Decadal trends associated with leading planetary wave regimes in the Southern Hemisphere (SH) are examined using the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. The leading regime indicated by the first EOF mode of 500 hPa height anomalies shows strong zonal symmetry and a phase reversal between high and midlatitudes. Positive height anomalies over high latitudes are accompanied by negative anomalies centered over three oceans. This mode has strong decadal variability associated with the height variations over the Antarctica. The heights or sea level pressure fell from 1965 to the present, while heights or pressure over the oceans increased. The wave 3 pattern strengthened in midlatitudes from 1980 to the present. These changes are related to the changes of the half yearly wave. The sudden change at midlatitude and high latitudes after 1975 observed in the Australian analysis also exists in the NCEP reanalysis.

The next two patterns are two Pacific South American (PSA) patterns. They depict wave number 3 in quadrature with each other with large amplitudes in the PSA sector. The wave train from the Pacific to South America suggests that these patterns are forced from the Tropics.