Publication Abstracts
Esposito and Travis 1982
Esposito, L.W., and , 1982: Polarization studies of the Venus UV contrasts: Cloud height and haze variability. Icarus, 51, 374-390, doi:10.1016/0019-1035(82)90090-2.
Polarimetry is able to show direct evidence for compositional differences in the Venus clouds. We present observations (collected during 22 and 1/2 Venus years by the Pioneer Venus Orbiter) of the polarization in four colors of the bright and dark ultraviolet features. We find that the polarization is significantly different between the bright and dark areas. The data show that the "null" model of L.W. Esposito (1980, J. Geophys. Res. 85, 8151-8157) and the "overlying haze" model of J.B. Pollack et al. (1980, J. Geophys. Res. 85, 8223-8231) are insufficient. Exact calculations of the polarization, including multiple scattering and vertical inhomogeneity near the Venus cloud tops, are able to match the observations. Our results give a straightforward interpretation of the polarization differences in terms of known constituents of the Venus atmosphere. The subµm haze and UV absorbers are anticorrelated; for haze properties as given by K. Kawabata et al. (1980, J. Geophys. Res. 85, 8129-8140) the excess haze depth at 9350 Å over the bright regions is Δtauh = 0.03±0.02. The cloud top is slightly lower in the dark features; the extra optical depth at 2700 Å in Rayleigh scattering above the darker areas is ΔtauR = 0.010±0.005. This corresponds to a height difference of 1.2±0.6 km at the cloud tops. The calculated polarization which matches our data also explains the relative polarization of bright and dark features observed by Mariner 10. The observed differential polarization cannot be explained by differential distribution of haze, if the haze aerosols have an effective size of 0.49 µm, as determined by K. Kawabata et al. (1982, submitted) for the aerosols overlying the Venus equator. We propose two models for the UV vertical contrasts consistent with our results. In a physical model, the dark UV regions are locations of vertical convergence and horizontal difergence. In a chemical model, we propose that the photochemistry is limited by local variations in water vapor and molecular oxygen. The portions of the atmosphere where these constituents are depleted at the cloud tops are the dark UV features. Strong support for this chemical explanation is the observation that the number of sulfur atoms above the cloud tops is equal over both the bright and dark areas. The mass budget of sulfur at these altitudes is balanced between excess sulfuric haze over the bright regions and excess SO2 in the dark regions.
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BibTeX Citation
@article{es03000u,
author={Esposito, L. W. and Travis, L. D.},
title={Polarization studies of the Venus UV contrasts: Cloud height and haze variability},
year={1982},
journal={Icarus},
volume={51},
pages={374--390},
doi={10.1016/0019-1035(82)90090-2},
}
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RIS Citation
TY - JOUR ID - es03000u AU - Esposito, L. W. AU - Travis, L. D. PY - 1982 TI - Polarization studies of the Venus UV contrasts: Cloud height and haze variability JA - Icarus JO - Icarus VL - 51 SP - 374 EP - 390 DO - 10.1016/0019-1035(82)90090-2 ER -
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