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| Titel |
Retrieval of Venus' clouds parameters with polarization using SPICAV-IR onboard Venus Express |
| VerfasserIn |
Loic Rossi, Emmanuel Marcq, Franck Montmessin, Anna Fedorova, Daphne Stam, Jean-Loup Bertaux, Oleg Korablev |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250102345
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| Publikation (Nr.) |
 EGU/EGU2015-1656.pdf |
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| Zusammenfassung |
| Understanding the structure and dynamics of Venus’ clouds is essential as they have a
strong impact on the radiative balance and atmospheric chemistry of the planet.
Polarimetry has greatly contributed to our knwoledge about the properties of the
cloud layers located between 48 and ~ 70 km. Hansen and Hovenier (1974), using
ground-based observations, found the cloud particles to be ~ 1μm spherical droplets, with
a refractive index corresponding to a concentrated sulfuric acid-water solution.
Later, Kawabata et al. (1980), using polarimetric data from OCPP onboard Pioneer
Venus retrieved the properties of the haze: effective radius of ~ 0.25μm, refractive
indices consistent with a sulfuric acid-water solution, variance of the particle size
distribution.
We introduce here new measurements obtained with the SPICAV-IR spectrometer
onboard ESA’s Venus Express. Observing Venus in the visible and IR from 650Ânm to
1625Ânm with a good spatial and temporal converage, SPICAV’s sensitivity to the
degree of linear polarization gives us an opportunity to put better constraints on
haze and cloud particles at Venus cloud top, as well as their spatial and temporal
variability.
These observations reveal a particular feature called glory, observed by SPICAV-IR and
VMC (Markiewicz et al. 2014). Using a radiative transfer code taking into account
polarization (de Haan et al. 1987, de Rooij et al. 1984, Stam et al. 1999), we model the cloud
layers and the glory allowing us to retrieve the real part of the refractive index, the effective
radius and variance of the particle size distribution from the main cloud layer. Our results
confirm that the particles are spherical, with a narrow size distribution and with refractive
indices that are compatible with H2SO4-H2O solutions (Rossi et al. 2014). Using the large
latitudinal coverage of the data, we can also retrieve the variation of the overlying haze
layer optical thickness. We find that Ïh is increasing with increasing latitude, in
agreement with previous measurements from Braak et al. (2002) and Knibbe et al.
(1997).
References
Hansen, J.ÂE. and Hovenier, J.ÂW., 1974, Interpretation of the polarization of
Venus., Journal of Atmospheric Sciences, 31.
Kawabata et al., 1980, Cloud and haze properties from Pioneer Venus
Polarimetry, J. Geophys. Res., 85.
Markiewicz, W.J. et al., 2014, Glory on venus cloud tops and the unknown UV
absorber, Icarus, 234.
de Haan, J.ÂF. et al, 1987, The adding method for multiple scattering calculations
of polarized light, Astron. Astrophys., 183.
de Rooij, W.ÂA. and van der Stap, C.ÂC.ÂA.ÂH., 1984, Expansion of Mie
scattering matrices in generalized spherical functions, Astron. Astrophys., 131
Stam, D.ÂM. et al., 1999, Degree of linear polarization of light emerging from
the cloudless atmosphere in the oxygen A band, J. Geophys. Res., 104.
Rossi, L. et al., 2014, Preliminary study of Venus cloud layers with polarimetric
data from SPICAV/VEx, Planet. Space Sci., In Press.
Braak, C.ÂJ. et al., 2002, Spatial and temporal variations of Venus haze properties
obtained from Pioneer Venus Orbiter polarimetry, J. Geophys. Res. (Planets),
107.
Knibbe, W.ÂJ.ÂJ. et al., 1997,A biwavelength analysis of Pioneer Venus
polarization observations, J. Geophys. Res., 102. |
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