An overview of POAM II aerosol measurements at 1.06 mu m

We present aerosol measurements by the Polar Ozone and Aerosol Measurement (POAM) II instrument, from November 1993 through February 1996. Aerosol extinction profiles are in good agreement with coincident SAGE II measurements from 15 to 24 km. Extinction is continuing to decline since the eruption of Mt. Pinatubo. Seasonal variation in extinction in both hemispheres is examined on constant ground-referenced and tropopause-referenced altitude surfaces. Aerosol extinction peaks in the winter in the north outside the vortex. This also appears to occur in the south, but cannot be followed throughout the winter since FOAM II measurements occur entirely inside the vortex at this time. A summer maximum at 19 km and above in the south is observed when the extinction ratio outside the vortex is plotted at a constant tropopause-referenced altitude. This is not true for the north. We conclude that in late spring in the south FOAM II is sampling low extinction, vortex-processed air, or that an unidentified mechanism operates in the south, but not in the north. Signatures of polar stratospheric clouds (PSCs) are prevalent in the southern hemisphere data. PSCs are also observed in the northern hemisphere, but much less frequently. Evidence of enhanced diabatic descent in the polar vortex in both hemispheres is observed at 500 and 600 K. At 400 K the distinction between extinction ratios inside and outside the vortex in early winter is not as clear as at higher altitudes.