Study of Venus cloud layers by polarimetry using SPICAV/VEx

Abstract : The study of Venus’s cloud layers is important in order to understand the structure, radiative balance and dynamics of the Venusian atmosphere. Polarization measurements have given important constraints for the determination of the constituents of the clouds. In 1974, Hansen & Hovenier used ground-based observations to establish that the main cloud particles are micrometric droplets of a concentrated sulfuric acid solution. The overlying haze has been identified as r ∼ 0.25 μm particles by Kawabata et al. (1980) using Pioneer Venus OCPP measurements. Temporal and spatial variability of the haze has also been observed. Our study uses the polarimetric data from the SPICAV-IR spectrometer onboard ESA’s Venus Express spacecraft. The degree of linear polarization of the light scattered at cloud top is measured in the 0.65 –1.7 μm range, with a global coverage of the northern hemisphere of Venus. The polarization observed is consistent with previous ground-based observations and with Pioneer Venus OCPP polarimetric measurements, yielding a negative polarization degree at all phase angles, corresponding to the micrometric, sulfuric acid, cloud particles. The polarization reaches strong positive values at high latitudes, indicating an increased contribution of the submicron haze. A polarization glory is observed on several orbits, and is used to put constraints on the refractive index, size and variance of the cloud particle distribution. We present here results of the modeling using the Doubling-adding method on the glory to characterize the cloud particles, and at higher latitudes to investigate the variation of the haze layer optical depth. We confirm that the clouds are made of ∼ 1 μm sulfuric acid droplets, and we observe an increase of the haze optical thickness with increasing latitude.
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Submitted on : Thursday, October 23, 2014 - 11:17:30 AM
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Loïc Rossi, Emmanuel Marcq, Franck Montmessin, Anna Fedorova, Daphne Stam, et al.. Study of Venus cloud layers by polarimetry using SPICAV/VEx. Astronomical Polarimetry 2014, May 2014, Grenoble, France. 2014, ⟨http://www.polarisation.eu/index.php/astropol-2014⟩. ⟨hal-01076799⟩

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