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| Titel |
Diurnal variation of atmospheric water vapor at Gale crater: Analysis from
ground-based measurements |
| VerfasserIn |
German Martinez, Timothy McConnochie, Nilton Renno, Pierre-Yves Meslin, Erik Fischer, Alvaro Vicente-Retortillo, Caue Borlina, Osku Kemppinen, Maria Genzer, Ari-Matti Harri, Manuel de la Torre-Juárez, Mari-Paz Zorzano, Javier Martín-Torres, Nathan Bridges, Sylvestre Maurice, Olivier Gasnault, Javier Gomez-Elvira, Roger Wiens |
| 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 |
250129219
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| Publikation (Nr.) |
 EGU/EGU2016-9297.pdf |
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| Zusammenfassung |
| We analyze measurements obtained by Curiosity’s Rover Environmental Monitoring Station
(REMS) and ChemCam (CCAM) instruments to shed light on the hydrological
cycle at Gale crater. In particular, we use nighttime REMS measurements taken
when the atmospheric volume mixing ratio (VMR) and its uncertainty are the lowest
(between 05:00 and 06:00 LTST) [1], and daytime CCAM passive sky measurements
taken when the VMR is expected to be the highest (between 10:00 and 14:00 LTST)
[2].
VMR is calculated from simultaneous REMS measurements of pressure (P), temperature
(T) and relative humidity (RH) at 1.6 m (VMR is defined as RH×es(T)/P , where es is the
saturation water vapor pressure over ice). The REMS relative humidity sensor has
recently been recalibrated (June 2015), providing RH values slightly lower than those
in the previous calibration (Dec 2014). The full diurnal cycle of VMR cannot be
analyzed using only REMS data because the uncertainty in daytime VMR derived from
REMS measurements is extremely high. Daytime VMR is inferred by fitting the
output of a multiple-scattering discrete-ordinates radiative transfer model to CCAM
passive sky observations [3]. CCAM makes these observations predominately in the
vicinity of 11:00 – 12:00 LTST, but occasionally in the early morning near 08:00
LTST.
We find that throughout the Martian year, the daytime VMR is higher than at night, with a
maximum day-to-night ratio of about 6 during winter. Various processes might explain the
differences between nighttime REMS and daytime CCAM VMR values. Potential
explanations include: (i) surface nighttime frost formation followed by daytime sublimation
[1], (ii) surface nighttime adsorption of water vapor by the regolith followed by daytime
desorption and (iii) large scale circulations changing vertical H2O profiles at different times
of the year. Potential formation of surface frost can only occur in late fall and winter [1],
coinciding with the time when the diurnal amplitude of the near-surface VMR at Gale is
maximum, while adsorption/desorption by the regolith can occur throughout the year [2].
Adsorption by the regolith is expected to be more efficient at lower temperatures (i.e. winter),
although it remains unclear whether kinetics would allow for the exchange of adsorbed water
on hourly time scales necessary to track insolation [4-5]. Local surface-atmosphere
interactions, either via frost formation and/or exchange of adsorbed water with
the atmosphere, might play a significant role in the diurnal hydrological cycle at
Gale.
REFERENCES:
[1] Martínez G. M. et al. (2016) Icarus, doi: http://dx.doi.org/10.1016/j.icarus.2015.12.004
[2] Savijärvi H. (2016) Icarus, 265, 63–69.
[3] McConnochie T. et al. (2015) AGU Fall Meeting.
[4] Beck P. et al. (2010) JGR, 115, E10011.
[5] Zent A. P. et al. (2001) JGR, 106, 14667-14674. |
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