Lidar observations collected during winter 1995 at McMurdo Station, An
tarctica (78 degrees S-167 degrees E), are analyzed to determine polar
stratospheric cloud (PSC) physical properties. A scheme to infer PSC
phase from lidar depolarization and backscatter profiles is presented.
Interpretation is supported by collocated temperature soundings and b
y isentropic back trajectories. The analysis shows that first appearan
ce of PSC is consistent with frozen sulfates, mixing with liquid terna
ry solutions (H2SO4-HNO3-H2O) when temperature lowers. Finally, solids
consistent with HNO3 mixing ratios form as mixed phases first, then f
ollowed by full solid phases. Mixed phases (i.e., coexisting solid and
liquid aerosols) are detected during the whole winter. While mixed ph
ase PSCs form particularly in the altitude range 15-20 km and are the
last to disappear, full solid phases are mainly observed above 20 km a
nd last until the end of August. Mixed phases possess the largest PSC
surface areas and, as a result of selective growth, can reach large, f
ast settling sizes. The considerable denitrification and halogen activ
ation observed in the Antarctic lower stratosphere, where the ozone ho
le takes place, appears to be well correlated with the action of this
kind of PSC.