The Seasonal Reversal of the Stratospheric Circulation

Abstract

The mean and individual seasonal reversal progressions are described for each of the 11 years of available rocket observations from 80°N to 80°S, and from 20 to 65 km. Isochrone sections were based on the time sections of the preceding paper and on frequencies of east-west wind data. In the Northern Hemisphere the mean spring reversal starts in early April at highest altitudes and progresses downward and southward. The mean fall reversal proceeds simultaneously both upward from 20 km and downward from 60 km at high latitudes and then southward and downward. Both the onset and direction of the spring reversal are highly irregular from year to year, but the fall process is very uniform and rapid, starting in August and reaching 20 km in the subtropics in two months. The Southern Hemisphere spring reversal appears to move from low to high latitudes oppositely to that in the Northern Hemisphere, and downward, taking about three months to reach 60°S at 20 km. The Southern Hemisphere fall proceeds to low latitudes and altitudes from both highest subtropical altitudes and lowest polar altitudes. The local nature of spring reversals for individual years is stressed.