POAM III measurements of dehydration in the Antarctic lower stratosphere

We present measurements of stratospheric water vapor and aerosols in the Antarctic from the POAM III instrument during the period April through December 1998. The measured variations in water vapor enable us to study both descent in the vortex and the effect of dehydration that occurs in the lower stratosphere below ∼23 km when the temperature drops below the frost point in July. There is a temporal correlation between the dehydration that occurs in July and an increase in high aerosol optical depth events in the lower stratosphere, suggesting that these events are due to the presence of ice PSC's. When temperatures warm up there is some rehydration at the highest altitudes of the dehydrated region (∼20–23 km), probably resulting from descent within the vortex. At ∼12 km rehydration is probably the result of mixing in of air from outside the vortex. The temperature increase in October produces little rehydration at 17 km and no clear rehydration at 14 km, suggesting that the water has precipitated out of these layers.