Stratospheric Aerosol Measurements III: Optical Model Calculations

Abstract

Mie single scattering, absorption, and total extinction calculations for various size distribution and composition models of the stratospheric aerosol are presented. These models are derived from global in-situ measurements made with a balloon-borne photoelectric particle counter during the period December 1971 through July 1974. The models are in agreement with simultaneous aerosol mass measurements made by aircraft filter sampling and by balloon-borne impactor over Laramie, Wyo. Nominal stratospheric aerosol optical depths at 0.53 µm wavelength are 0.005 to 0.007. The maximum stratospheric aerosol absorption cross section at this wavelength is 0.04×10⁻³ km⁻¹ at 18–20 km altitude, assuming a refractive index imaginary part of 0.01. The predicted 180° backscatter lidar return at the 18–20 km altitude of maximum aerosol mixing ratio is 9% to 17% of the Rayleigh return at a wavelength of 0.6943 µm for the various aerosol models. Measured and predicted lidar returns over Laramie in September 1972 are in good agreement for several of the size distribution and composition models used here. Values of the global stratospheric aerosol albedo at 0.53 µm are 0.002 to 0.003.