Aerosol surface areas deduced from early 1993 SAGE II data and comparisons with stratospheric photochemistry, aerosols, and dynamics expedition measurements

Abstract

Stratospheric Aerosol and Gas Experiment II (SAGE II) multi‐wavelength stratospheric aerosol extinction measurements are used to estimate near‐global distributions of aerosol surface area density for early months of 1993. A comparison of monthly contour plots shows that the aerosol surface area density above the tropopause gradually decreased from about 15 µm²cm−3 in January 1993 to about 10 µm²cm−3 in May 1993. Aerosol surface area density profiles measured by the Forward Scattering Spectrometer Probe (FSSP‐300) during the Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE) campaign in May 1993 are compared with estimated SAGE II surface area density profiles obtained at nearby locations. FSSP measurements are in general, slightly lower than the SAGE II measurements. The possible sources of this discrepancy are discussed. When 4‐day average FSSP measurements are compared with the SAGE II zonal mean profile for May 1993 and 35°N–40°N at altitudes above 16 km, the agreement is good. In addition, SAGE II aerosol surface area density profiles calculated by assuming a lognormal size distribution and by using principal component analysis are compared, good agreement is shown at high altitudes. However, at low altitudes their differences may be as high as 25%.