Quasi-Biennial and Long-Term Fluctuations in Tropopause Pressure and Temperature, and the Relation to Stratospheric Water Vapor Content

Abstract

Quasi-biennial and long-term fluctuations in tropopause temperature and pressure are determined at 10 stations in tropical and Northern Hemisphere temperate and polar latitudes for the approximate period 1960–1970. In tropical latitudes there is a correlation, r, of 0.81 between quasi-biennial oscillations in tropopause pressure and 50-mb zonal wind, with the tropopause pressure about 4 mb higher than normal at the time of quasi-biennial west wind maximum. There is a strong out-of-phase relation (r=−0.70) between quasi-biennial oscillations in tropopause pressure in tropical and temperate latitudes. All stations show an overall long-term increase in tropopause pressure, with values varying from 5–7 mb per decade in the tropics to 2–4 mb per decade in temperate-polar latitudes. This increase appears to have begun about 1957 but there is some evidence that it is now ending. Associated with this increase in tropopause pressure is an increase in tropopause temperature, and the possibility is considered that the increase in water vapor mixing ratio in the low stratosphere at Washington, D. C., between 1964 and 1970 is associated with the increase in tropopause temperature observed at most tropical and subtropical stations after 1960. Constant level balloon flights at 200 mb in Southern Hemisphere temperate latitudes provide evidence for a quasi-biennial oscillation in meridional wind nearly in phase with tropopause temperature, which wind would aid in the poleward transport of the excess stratospheric water vapor presumably associated with a warm tropical tropopause. The probable influence of the Mt. Agung volcanic eruption on tropopause temperature and pressure is indicated.