Comparison of polar ozone and aerosol measurement (POAM) II and stratospheric aerosol and gas experiment (SAGE) II aerosol measurements from 1994 to 1996

We describe statistical comparisons between version 6.0 Polar Ozone and Aer osol Measurement (POAM) II and version 5.931 Stratospheric Aerosol and Gas Experiment (SAGE) II measurements of aerosol extinction and derived surface area and volume density between 1994 and 1996. Qualitatively, both instrum ents show similar decay of the aerosol extinction at visible and near-IR wa velengths in the altitude range from 12 to 30 km, resulting from dissipatio n of the Mount Pinatubo aerosols. We present quantitative differences betwe en the SAGE II and FOAM II extinctions at 1 and 0.45 mu m for temporally an d spatially coincident measurements. On average, for the moderately elevate d aerosol extinction levels encountered in 1994, differences in the extinct ion at higher and lower altitudes. Differences at 0.45 mu m are within +/-3 5% between 13 and 30 km, increasing at lower altitudes. For the lower aeros ol extinction conditions of 1995 and 1996, the comparisons indicate that sy stematic errors contributed to larger relative differences between the inst ruments. These effects are manifested as "asymmetries" in the Northern Hemi sphere versus Southern Hemisphere comparisons, and in the 1 mu m versus 0.4 5 mu m comparisons. We suggest that these systematic differences are partly due to altitude registration errors in one or both of the instruments. Ave rage volume densities derived using a principal component analysis techniqu e agreed within about 10% at high northern latitudes between 16 and 27 km, and within about 30% at high southern latitudes. In most cases, surface are a density differences were somewhat larger. Although a dedicated validation campaign was not feasible for FOAM II, overall the results presented here confirm the validity of the FOAM II aerosol measurements for scientific stu dies.