Evidence of Polar-Tropical Coupling in Upper Stratospheric Zonal Wind Anomalies

Abstract

Evidence linking long-period, large-scale zonal wind anomalies in the tropical upper stratosphere to those in the winter hemisphere is discussed in the light of current thinking on planetary-scale wave propagation and zonal flow interaction in the stratosphere. The evidence appears to confirm the hypothesis that absorption of planetary waves at the zero zonal wind line is the source of easterly momentum for the easterly regime of the semiannual zonal wind oscillation. Harmonic analysis of the zonal wind data for stations ranging from 31S to 64N reveals that the semiannual cycle is almost symmetrical about the equator but that the amplitude is somewhat greater a short distance to the south and the phase somewhat advanced a short distance to the north. These asymmetries can be accounted for by the wave absorption hypothesis.