The Southern Oscillation. Part V: The Anomalies in the Lower Stratosphere of the Northern Hemisphere in Winter and a Comparison with the Quasi-Biennial Oscillation

Abstract

The mean anomalies of 50 mb height in the northern winter for seven Warm Events in the Southern Oscillation show a weak polar vortex and an enhanced Aleutian high. In the mean for six Cold Events the polar vortex is unusually strong and the Aleutian high is weakened and displaced far to the southwest. These anomalies are consistent with the corresponding anomalies in sea level pressure pattern. The Warm Events of 1963 and 1982 did not fit this pattern as in both years the polar vortex was cold and intense. These events happened in years when volcanoes injected large amounts of gases and aerosols into the stratosphere and the temperature of the tropical stratosphere became unusually high. In other Warm Events the temperature of the tropical stratosphere was abnormally low. The mean anomalies of the Quasi-Biennial Oscillation for the winter as a whole (west minus east phase) computed from years with no Cold or Warm Events are zonally symmetrical and shaped as four concentric regions with alternating sign, the polar vortex being centered near the North Pole and strong in the west phase of the QBO. The anomalies of the Warm Events in the Southern Oscillation, the years of which are almost equally distributed between years of west and east phase of the QBO, are in contrast not zonally symmetrical for the winter as a whole as the influence of the SO is to strengthen substantially the Aleutian high in the stratosphere.