IN-SITU OBSERVATIONS OF AN ANTARCTIC POLAR STRATOSPHERIC CLOUD - SIMILARITIES WITH ARCTIC OBSERVATIONS

Measured particle volumes in a type I polar stratospheric cloud near t he Antarctic polar vortex during ASHOE/MAESA show that the onset of th e cloud occurred near 193 K, 3 degrees colder than nitric acid trihydr ate (NAT) saturation. The onset temperature, the smooth increase of vo lume with decreasing temperature, the inverse correlation of particle volume and enhanced NOy (HNO3 in the particles) with temperature, and comparisons of observations with an equilibrium model of ternary dropl et growth all support the notion that much of this type I PSC was tern ary solution droplets. This provides confirmation of previous findings in the northern hemisphere. However, the ternary model does not fit t he observations in all regions. This may be due to the presence of som e solid phase growth in agreement with impactor observations.