| Characteristics of quasi-stationary (QS) waves in the Southern Hemisphere are
discussed using 49 years (1950–1998) of NCEP/NCAR reanalysis data. A comparison
between the stationary wave amplitudes and phases between the recent data (1979–1998)
and the entire 49 years data showed that the differences are not large and the 49 years data
can be used for the study. Using the 49 years of data it is found that the amplitude of QS
wave 1 has two maxima in the upper atmosphere, one at 30°S and the other at 55°S. QS
waves 2 and 3 have much less amplitude. Monthly variation of the amplitude of QS wave 1
shows that it is highest in October, particularly in the upper troposphere and stratosphere.
To examine the QS wave propagation Plumb's methodology is used. A comparison
of Eliassen-Palm fluxes for El Niño and La Niña events showed that during El Niño events
there is a stronger upward and equatorward propagation of QS waves, particularly in the
austral spring. Higher upward propagation indicates higher energy transport. A clear wave
train can be identified at 300hPa in all the seasons except in summer. The horizontal
component of wave activity flux in the El Niño composite seems to be a Rossby wave
propagating along a Rossby wave guide, at first poleward until it reaches its turning
latitude in the Southern Hemisphere midlatitudes, then equatorward in the vicinity of
South America. The position of the center of positive anomalies in the austral spring
in the El Niño years over the southeast Pacific, near South America, favors the occurrence of blocking
highs in this region. This agrees with a recent numerical study by Renwick and Revell (1999).
Key words. Meteorology and atmospheric dynamics (climatology;
general circulation; ocean-atmosphere interactions) |