DOWNWARD TRANSPORT IN THE UPPER-STRATOSPHERE DURING THE MINOR WARMINGIN FEBRUARY 1979

On February 6, 1979, a small region of dry air, referred to below as a dry tongue, appeared in Limb Infrared Monitor of the Stratosphere dat a directly below the stratopause at approximately 75 degrees N when a zonal average between 40 degrees E and 160 degrees E was applied. Isen tropic analysis of Ertel's potential vorticity and H2O mixing ratio do es not support the hypothesis of the dry tongue being caused solely by adiabatic sinking from the dry mesosphere into the upper stratosphere . Therefore a three-dimensional mechanistic model of the middle atmosp here, which is mainly driven by the net heating rate and the effects o f breaking gravity waves, is used to simulate the minor warming in Jan uary and February 1979. The model data clearly support the existence o f the dry tongue mentioned above as a real phenomenon. Moreover, they allow the dry tongue to be interpreted as the result of the combined a diabatic and diabatic downward movements east of the center of the pol ar vortex.