The evolution of the dehydration in the Antarctic stratospheric vortex

An intensive program of balloon-borne frost point measurements together with several soundings from the South Pole give a comprehensive picture of the general development of the dehydration in the Antarctic stratospheric vortex. The period of dehydration typically starts around the middle of June, and a rapid formation of large particles leads to a fast dehydration of the vortex. The evaporation of falling particles leads to rehydration layers, which have significantly higher water vapor concentrations than the undisturbed stratosphere. A small cold region inside the vortex seems to be sufficient to dehydrate the entire vortex. Above 20 km the dehydration is completed by the end of July. From the descent of the upper dehydration edge a mean descent rate inside the vortex of 1.5 km/month can be estimated. A sounding at South Pole shows that the dehydration may persist into November and indicates that there is no significant transport into the vortex throughout the winter and early spring. (from Authors)