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| Titel |
Mesospheric CO2 ice clouds on Mars observed by Planetary Fourier Spectrometer onboard Mars Express |
| VerfasserIn |
Shohei Aoki, Marco Giuranna, Yuki Sato, Hiromu Nakagawa, Takao M. Sato, Paulina Wolkenberg, Isao Murata, Yasumasa Kasaba |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128347
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| Publikation (Nr.) |
 EGU/EGU2016-8330.pdf |
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| Zusammenfassung |
| We investigate mesospheric CO2 ice clouds on Mars detected by the Planetary
Fourier Spectrometer (PFS) onboard Mars Express (MEx). The relatively high
spectral resolution of PFS allows firm identification of the clouds’ reflection spike.
A total of 279 occurrences of the CO2 ice clouds features has been detected at
the bottom of 4.3 μm CO2 band from the MEx/PFS data during the period from
MY27 to MY32. 115 occurrences out of them are also confirmed by simultaneous
observations by MEx/OMEGA imaging spectrometer. The spatial and seasonal
distributions of the CO2 ice clouds observed by PFS are consistent with the previous
studies: the CO2 ice clouds are only observed between Ls=0∘ and 140∘ at distinct
longitudinal corridors around the equatorial region (±20∘N). The CO2 ice clouds are
preferentially detected at local time between 15-17h. The relatively high spectral resolution
of PFS allows us to investigate the spectral shape of the CO2 ice clouds features.
The CO2 ice clouds reflection spike is peaked between 4.24 and 4.29 μm, with
no evidence of the secondary peak at 4.32-4.34 μm observed by MEx/OMEGA
(Määttänen et al., 2010). In most of the cases (about 75%), the peak is present
between 4.245 and 4.255 μm. Moreover, small secondary peaks are found around
4.28 μm (about 15 occurrences). These spectral features cannot be reproduced
by the synthetic spectra with the assumption of a spherical particle shape in our
radiative transfer model (DISORT). This can be due to the fact that the available CO2
ice reflective indexes are either inaccurate or inappropriate for the mesospheric
temperatures, or that the particle shape is not spherical. Accurate measurements of
the reflective index depending on temperature and detailed comparison with the
model taking into account non-spherical shapes will give a clue to solve this issue. |
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