A quasi-biennial standing wave in the Southern Hemisphere and interrelations with sea surface temperature

Abstract

An empirical orthogonal function analysis is performed on monthly mean sea level pressure (SLP) deviations from normal (anomalies) in the Australasian area and monthly mean sea surface temperature (SST) anomalies in the Tasman Sea for 14 years of data. Only the five components of each that explain most of the variance appear to be significant. Spectral and cross-spectral analysis of the time series of the coefficients reveals significant relations at a quasi-biennial periodicity. An empirical model of the SLP and SST fields for this period is constructed and the amplitudes of the oscillation are found to be about 2 1/2 mb in the monthly mean SLP anomaly field and 0·4 degC in the monthly mean SST anomaly field. Physical and statistical indications are that the SST field is largely caused by the SLP field but some interdependence is present. The quasi-biennial SLP oscillation is related to Pittock's L-index and appears to correspond to a change in wavenumber 3 in the Southern Hemisphere atmospheric circulation. A phase change occurred at the end of 1970, but in even years prior to 1971, and in odd years since 1970, there were increased meridional transports throughout the troposphere and lower stratosphere by the large-scale eddies. A suggestion is made that changes in land–sea heating contrasts may be an important part of the mechanism.