Tale of the Tape: A Long-term Record of Vertical Transport in the Tropical Stratosphere Derived from Water Vapor Measurements

We use water vapor mixing ratios in the SWOOSH (Stratospheric Water and Ozone Satellite Homogenized) database to characterize the evolution of moist and dry anomalies in the tropical lower stratosphere, which are generated in the so-called “tape recorder” regime of the upward branch of the Brewer-Dobson circulation. Two methods have been developed for quantifying mean upward velocities from the tape recorder signal: a two-level time series approach, and a piecewise vertical profile analysis. The time series approach has been successfully used with continuous, daily satellite measurements records extending over slightly one decade. However, this method is not easily applied to monthly means contained in multi-decadal, multi-platform datasets such as SWOOSH. We find that the vertical profile approach is better suited for estimating upward transport using monthly mean data, and that a quasi-continuous record of mean vertical velocity in the 40-60 hPa region can be derived from 1991 to the present. Our analysis shows the influence of seasonal cycles and the quasi-biennial oscillation in the long-term record of vertical transport.