Calculating the global mass exchange between stratosphere and troposphere

摘要

Large-scale cross-tropopause mass fluxes are diagnosed globally from 1979 to 1989 for northern hemisphere winter conditions (December, January, and February). Results of different methods with regard to the definition of the tropopause and the way to calculate the mass fluxes are compared and discussed. The general pattern of the mass exchange from the tropopause into the stratosphere and vice versa agrees fairly well when using different methods, but the absolute values can differ up to 100%. An inspection of the temporal development of the mass fluxes for solstice conditions indicates a complex picture: whereas a permanent significant downward flux from the stratosphere into the troposphere is detected for latitude regions between 25 N and 40 N and between 30 S and 50 S (initiated by the poleward branches of the Hadley Cells), a non-uniform behaviour is observed at higher latitude bands: time-periods of strong mass exchange from the troposphere into the stratosphere are disrupted by periods of an opposite mass exchange. Nevertheless, the calculated large-scale upward directed mass exchange through the tropopause seems not to have a significant impact for the composition of the stratosphere. (orig.)