Photopolarimetry analysis of the Venus atmosphere in polar regions

An analysis of linear polarization in the north and south polar regions of Venus observed by the Pioneer Venus orbiter during the first 2820 days of its mission has been performed to find microphysical properties of the submicrometer particles and to investigate the temporal variation of the optical thickness of the haze layer. The search for the best values of the physical properties and vertical distribution of the haze particles is based on minimization of the RMS discrepancy between the computed theoretical polarization and observed polarization, under the assumption that the variation of the observed polarization is due to the temporal variation of the optical thickness of the haze layer. This approach allows us to use a simple model which can explain well general features of the angular distribution of polarization for a large number of maps at wavelengths 935, 550, and 365 nm. We find that in the north polar region the haze particles have effective radius 0.25 +/- 0.05 mu m, effective variance 0.25 +/- 0.05, and real part of the refractive index 1.435 +/- 0.02 at wavelength 550 mm. In the south polar region, the haze particles have effective radius 0.29 +/- 0.02 mu m, effective variance 0.25 +/- 0.03, and real part of the refractive index 1.45 +/- 0.02 at wavelength 550 mm. Temporal variations of optical thickness of the haze particles in both polar regions seem to exhibit short-period quasi-oscillation features and our present analysis suggests some correlation between the variation in optical thickness of the haze layer in the north and south polar regions. (C) 1996 Academic Press, Inc.