CALCULATING THE GLOBAL MASS-EXCHANGE BETWEEN STRATOSPHERE AND TROPOSPHERE

Large-scale cross-tropopause mass fluxes are diagnosed globally from 1 979 to 1989 for Northern Hemisphere winter conditions (December, Janua ry, and February). Results of different methods of approaches with reg ard to the definition of the tropopause and the way to calculate the m ass fluxes are compared and discussed. The general pattern of the mass exchange from the tropopause into the stratosphere and vice versa agr ees fairly well when using different methods, but the absolute values can differ up to 100%. An inspection of the temporal development of th e mass fluxes for solstice conditions indicates a complex picture. Whe reas a permanent significant downward flux from the stratosphere into the troposphere is detected for latitude regions nearly between 25 deg rees N and 40 degrees N and between 30 degrees S and 50 degrees S (ini tiated by the poleward branches of the Hadley cells), a non-uniform be haviour is observed at higher latitude bands. Periods of strong mass e xchange from the troposphere into the stratosphere are disrupted by pe riods of an opposite mass exchange. A comparison of the stratoshere-tr oposphere (ST) exchange with the exchange at higher altitudes through surfaces, quasi-parallel to the tropopause, excludes a general connect ion. Only a few strong upward directed ST mass exchange events have co unterparts at higher altitudes. The composition of the stratosphere ma y be influenced directly by the ST exchange only in a thin layer above the tropopause.