A Partial Theory of the 26-Month Oscillation of the Zonal Wind in the Equatorial Stratosphere

Abstract

Abstract Attempted explanations of the 26-month zonal wind oscillation in the equatorial stratosphere are critically examined. Explanations in terms of subharmonic response, ‘vacillation,’ or a resonant mode are rejected. Some indirect astronomical and terrestrial evidence of a fluctuation of solar ultraviolet emission is noted, and, in view of the inadequacy of other explanations, appears to be a probable cause. A simple derivation is given of the thermal and geostrophic wind fields which propagate downward by eddy and radiative transfer through the equatorial stratosphere from a layer somewhere above 25 km which is periodically heated, presumably by a solar source of 26-month period. The wind field is shown to lag the temperature field by about 3 months in the vicinity of the equator, in agreement with available observations. The thermal and geostrophic wind disturbances propagate downward about 1 km mo−1 for an effective conductivity (sum of eddy and radiative conductivities) of the order of 104 cm2 se...