A New Formulation of the Exchange of Mass and Trace Constituents between the Stratosphere and Troposphere

Abstract

Using a dynamical definition of the tropopause, a diagnostic model of stratosphere?troposphere exchange is presented. The net transport across the tropopause is independent of the vertical coordinate. When the transport is partitioned into contributions from individual transport mechanisms, the isentropic coordinate system provides the most straightforward physical interpretation. The physical mechanisms responsible for the exchange of mass and trace constituents between the stratosphere and troposphere include diabatic processes, temporal movement of the tropopause, and transport along isentropic surfaces which intersect the tropopause. The mechanism of the isentropic transport operates in several meteorological settings of different spatial scales; the best-documented examples include tropopause folding near extratropical and subtropical jet streams and cutoff lows, as well as transverse circulations around quasi-steady jet streams. The relative importance of various mechanisms in the stratosphere?troposphere exchange can be assessed if a quantitative evaluation, based upon the diagnostic model presented herein, is carried out for the global atmosphere. The diagnostic model is applicable to any fluid domain where exchange occurs across an internal boundary.