THE MASS FLUX ACROSS THE TROPOPAUSE - QUASI-GEOSTROPHIC THEORY

The mean meridional circulation in the troposphere is driven by eddy m omentum fluxes associated with baroclinic waves. The dynamics of these waves can be described qualitatively by quasi-geostrophic theory. Her e, the flow in the vicinity of the storm tracks is modelled using f-pl ane quasi-geostrophic theory with the tropopause represented as a near ly horizontal surface separating a troposphere of uniform potential vo rticity from a similarly uniform stratosphere. Combining an analysis o f the mean meridional mass-nux associated with decaying eddies and the cross-tropopause mass-flux generated in the same process, it is possi ble to estimate the net flux both in the zonal mean and in a quasi-Lag rangian mean framework. The quasi-Lagrangian mean is here defined as a n average along potential temperature contours on the tropopause. Cons istent with earlier numerical and observational studies, it is found t hat the zonal mean mass-flux is upwards poleward of the jet, whereas t he quasi-Lagrangian mean is downwards.