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| Titel |
Spatial and temporal variations of particle sizes in the upper clouds of Venus from the VMC/VEx data |
| VerfasserIn |
Oksana Shalygina, Elena Petrova, Wojciech J. Markiewicz |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142113
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| Publikation (Nr.) |
 EGU/EGU2017-5689.pdf |
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| Zusammenfassung |
| From 2006 to 2014 the Venus Express spacecraft successfully operated in orbit around Venus.
A large amount of wide-angle images of the planet was acquired with the Venus
Monitoring Camera (VMC) in four narrow spectral bands centered at 0.365 (UV), 0.513
(VIS), 0.965 (NIR1), and 1.01 (NIR2) micron [1, 2]. With the VMC, full glory on
the upper cloud deck of Venus was imaged for the first time [1]. In this work we
analyze a whole set of the VMC data obtained in UV, VIS, and NIR1 channels
and compare the phase profiles of brightness measured at phase angles less than
40∘ to the singe-scattering phase functions of particles of different sizes. From
the angular position of the glory features, the dominant size of scattering particles
and their refractive index have been retrieved, and their spatial (in latitude) and
temporal (in local time, LST) variations have been analyzed. We presented the
measured phase profiles in two ways: they were built for individual images and for
individual small regions observed in series of successive images. The analysis of
the data of both types has yielded the consistent results, and they are in general
agreement with our estimates of the sizes and refractive index of cloud particles earlier
obtained from the phase-function analysis of the VMC data [1–3]. The presently
retrieved radii of cloud particles average approximately 1.0 – 1.2 μm (with peaks to 1.4
μm) and demonstrate a variable pattern versus latitude and LST. The decrease of
particle sizes at high latitudes (down to 0.6 μm) earlier observed in the NIR1 and
partly UV data has been definitely confirmed in the analysis of the data of all three
channels considered. The obtained values of the refractive index are more or less
uniformly distributed over the covered latitude and LST ranges, and most of them are
higher than those of concentrated sulfuric acid solution expected. This confirms
our previous result obtained only for the NIR1 spectral range, and now we may
state that the cases of a relatively high real part of the refractive index are often
observed for the 1-μm mode of cloud particles on Venus. Consequently, an additional
component with a high value of the refractive index is required to be present in the
cloud droplets. We suppose that this material can be ferric chloride or sulfur; both
are also candidates for the so-called unknown UV absorber in the upper clouds of
Venus.
References
[1] Markiewicz, W. J. et al. (2014), Icarus, 234, pp. 200–203,
doi:10.1016/j.icarus.2014.01.030.
[2] Shalygina, O. S. et al. (2015), PSS, 113–114, pp. 135–158, doi:
10.1016/j.pss.2014.11.012.
[3] Petrova, E. V. et al. (2015), PSS, 113–114, pp. 120–134,
doi:10.1016/j.pss.2014.11.013. |
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