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Scattering particles in nightside limb observations of Venus’ upper atmosphere by Venus Express VIRTIS |
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| Authors: | R de Kok PGJ Irwin G Piccioni |
| Institution: | a SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands b Atmospheric, Oceanic & Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK c Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA d INAF-IASF, via del fosso del Cavaliere 100, 00133 Rome, Italy e LESIA, Observatoire de Paris, CNRS, UPMC, Universit Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France |
| Abstract: | Nightside infrared limb spectra of the Venus upper atmosphere, obtained by Venus Express VIRTIS, show strong scattering of thermal radiation. This scattering of upward-going radiation into the line-of-sight is dominant below 82.5 km even at a wavelength of 5 μm, which is indicative of relatively large particles. We show that 1 μm-sized sulfuric acid particles (also known as mode 2 particles) provide a good fit to the VIRTIS limb data at high altitudes. We retrieve vertical profiles of the mode 2 number density between 75 and 90 km at two latitude ranges: 20-30°N and 47-50°N. Between 20 and 30°N, scattering by mode 2 particles is the main source of radiance for altitudes between 80 and 85 km. Above altitudes of 85 km smaller particles can also be used to fit the spectra. Between 47 and 50°N mode 2 number densities are generally lower than between 20 and 30°N and the profiles show more variability. This is consistent with the 47-50° latitude region being at the boundary between the low latitudes and high latitudes, with the latter showing lower cloud tops and higher ultraviolet brightness (Titov, D.V., Taylor, F.W., Svedhem, H., Ignatiev, N.I., Markiewicz, W.J., Piccioni, G., Drossart, P. 2008]. Nature 456, 620-623). |
| Keywords: | Venus Atmosphere Atmospheres Composition Infrared observations |
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