Optical sky polarimetry and photometry at Mauna Loa Observatory affected by stratospheric dust from El Chichon

Abstract

The Dave vector model is shown to be a good representation of the atmospheric effects on the photometry and polarimetry of the sky above Mauna Loa Observatory (MLO) on 6 Nov. 1982 produced by the El Chichon veil. Observations and modeling were accomplished at 0.36, 0.400, and 0.500 μm based on fundamental aerosol data. The effects of nonsphericity of the aerosols are included as a previously validated approximation in the input data. Extensive use was made of ground and air truth data available at MLO and the National Weather Service. From the modeling, the vertical number density of the El Chichon aerosol is deduced. The sky is found to be unusually bright from the aerosol scattering (radiance of 0.4 MW/m2/sr at a wavelength of 0.500 μm in the southerly and westerly directions at a sensor zenith angle of 60°) and the corresponding percent polarization low (~3%). Associated meteorological observations indicate stratospheric heating.