AEROSOL SURFACE-AREAS DEDUCED FROM EARLY 1993 SAGE-II DATA AND COMPARISONS WITH STRATOSPHERIC PHOTOCHEMISTRY, AEROSOLS, AND DYNAMICS EXPEDITION MEASUREMENTS

Stratospheric Aerosol and Gas Experiment II (SAGE II) multi-wavelength stratospheric aerosol extinction measurements are used to estimate ne ar-global distributions of aerosol surface area density for early mont hs of 1993. A comparison of monthly contour plots shows that the aeros ol surface area density above the tropopause gradually decreased from about 15 mu m(2)cm(-3) in January 1993 to about 10 mu m(2)cm(-3) in Ma y 1993. Aerosol surface area density profiles measured by the Forward Scattering Spectrometer Probe (FSSP-300) during the Stratospheric Phot ochemistry, Aerosols and Dynamics Expedition (SPADE) campaign in May 1 993 are compared with estimated SAGE II surface area density profiles obtained at nearby locations. FSSP measurements are in general, slight ly lower than the SAGE II measurements. The possible sources of this d iscrepancy are discussed. When 4-day average FSSP measurements are com pared with the SAGE II zonal mean profile for May 1993 and 35 degrees N-40 degrees N at altitudes above 16 km, the agreement is good. In add ition, SAGE II aerosol surface area density profiles calculated by ass uming a lognormal size distribution and by using principal component a nalysis are compared, good agreement is shown at high altitudes. Howev er, at low altitudes their differences may be as high as 25%.