Observations of Stratospheric Aerosol Using CPFM Polarized Limb Radiances

Abstract

The authors have used CPFM (composition and photodissociative flux measurement) polarized limb radiance measurements combined with a vector radiative transfer model to estimate stratospheric aerosol number density, extinction coefficient profiles, and size distribution. The CPFM spectroradiometer is flown on board the NASA ER-2 high-altitude research aircraft. The vertical and horizontal polarization components of limb radiance, nadir radiance, and horizontal flux are measured in the wavelength range 300?770 nm from approximately 5°?10° above to 5°?10° below the local horizon. Results from two flights during April and May 1997 as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer campaign are presented. Aerosol characteristics are determined by forcing the model radiances and polarization to match the measurements. Results indicate number densities at 20 km are roughly 5?6 cm?3 with an effective radius of 0.17?0.20 ?m. Number, surface area, and volume densities compare favorably with two in situ particle counters also flown on the ER-2.