The Annual Temperature Variation in the Lower Tropical Stratosphere

Abstract

The annual temperature variation in the lower tropical stratosphere has its maximum amplitude just above the equatorial tropopause and has nearly the same phase at a particular level throughout both hemispheres. Coldest temperatures occur during the Northern Hemisphere winter (January–February). It is hypothesized that the observed behavior is caused by a seasonal variation in the intensity of the Hadley cell of the Northern Hemisphere with strongest upwelling and cooling in the ascending branch of the meridional circulation occurring in January–February. Computations are made which suggest that a twofold increase in the upward motion near the equator from July to January is sufficient to account for the magnitude of the observed temperature decrease.