PHOTOPOLARIMETRY ANALYSIS OF THE VENUS ATMOSPHERE IN POLAR-REGIONS

An analysis of linear polarization in the north and south polar region s of Venus observed by the Pioneer Venus orbiter during the first 2820 days of its mission has been performed to find microphysical properti es of the submicrometer particles and to investigate the temporal vari ation of the optical thickness of the haze layer. The search for the b est values of the physical properties and vertical distribution of the haze particles is based on minimization of the RMS discrepancy betwee n the computed theoretical polarization and observed polarization, und er the assumption that the variation of the observed polarization is d ue to the temporal variation of the optical thickness of the haze laye r. This approach allows us to use a simple model which can explain wel l general features of the angular distribution of polarization for a l arge number of maps at wavelengths 935, 550, and 365 nm. We find that in the north polar region the haze particles have effective radius 0.2 5 +/- 0.05 mu m, effective variance 0.25 +/- 0.05, and real part of th e refractive index 1.435 +/- 0.02 at wavelength 550 mm. In the south p olar 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 optic al thickness of the haze particles in both polar regions seem to exhib it short-period quasi-oscillation features and our present analysis su ggests some correlation between the variation in optical thickness of the haze layer in the north and south polar regions. (C) 1996 Academic Press, Inc.