The Relation Between Equatorial Tropopause Temperature and Water Vapor Mixing Ratio in the Low Stratosphere at Washington, D.C.

Abstract

The Brewer-Dobson hypothesis that the stratospheric water vapor amount in temperate latitudes is governed by the water vapor removal capability (temperature) of the tropical tropopause is reexamined using the 11 years of stratospheric water vapor data obtained at Washington, D.C., by Mastenbrook. In the case of the annual variation, the tropopause temperature at equatorial stations Singapore and Gan is a maximum in August, whereas at Washington the water vapor mixing ratio is a maximum in October for the 100?80 mb layer and in March for the 70?50 mb layer. The 5-month difference in lag time implies a rather slow vertical mixing in the low stratosphere. These lag times correspond to mean meridional transport velocities of about 0.8 and 0.2 m s?1, respectively. In the case of the quasi-biennial oscillation, the mixing ratio in the 100?80 mb layer at Washington is a maximum 6 months after the tropopause-temperature maximum at Singapore and Gan, with the lag increasing to 12?13 months for the 70?50 mb layer. These lag times correspond to mean transport velocities of 0.3 and 0.1 m s?1, respectively. Over the 11?14 year period of record, the tropopause saturation mixing ratio at Singapore and Gan increased by about 0.5 ppm, whereas the stratospheric mixing ratio at Washington increased by 0.7 ppm, but this similarity in trend is not found at all stations. While these data tend in general to support the Brewer-Dobson concept, the relations are not sufficiently clear-cut as to completely deny other possibilities.