Abstract
A data set of monthly mean surface and sea-level pressure observations from a
number of stations in the Southern Hemisphere (SH) for the period since 1901 has
been used to investigate interannual and interdecadal variations of the SH
circulation. A fairly uniform network of 62 stations was selected with data for
the
period 1955-1985, with a reduced network of 35 stations having data for the
longer period 1901-1985. The sparse network has stations mainly on the SH
tropical and mid-latitude land masses, with few islands or high-latitude stations.
A rotated principal component analysis of the annual mean station pressure
anomalies has been used to describe the dominant modes of interannual and
interdecadal variations of the SH circulation that can be resolved with the
available station network. We show that the sparse station network is able to
capture the dominant modes of variability found in the period 1955-1985 using
the denser network. The leading mode is associated with the El Nino-Southern
Oscillation and is well resolved by the sparse network. This is the leading mode
for
interannual and interdecadal variations throughout the last century, but there are
periods when it has reduced variance and a somewhat different structure, notably
1916-1935. Other modes of interannual variations show marked changes in
importance on decadal or longer time-scales. [References: 25]