THE EXCHANGE OF AIR BETWEEN STRATOSPHERE AND TROPOSPHERE

Abstract

Stratospheric air is stably stratified, but vertical mixing is indicated by measurements of ozone and nuclear bomb debris. Tracer measurements suggest a mean net circulation by which air enters the stratosphere in the tropics, is transported polewards and leaves the stratosphere at higher latitudes. The air transport seems to be sufficient for full replacement of stratospheric air within two years. The tropical tropopause is regarded as the result of ascending cold air being mixed with warmer air from higher latitudes. The polar tropopause is regarded as the mixing layer between an upper current of stratospheric air going downwards and a lower region where convective currents occur. Springtime increase of ozone is thought to be due to subsidence associated with the breakdown of the stratospheric polar vortex, beginning at a high level.