Aphelion water‐ice cloud mapping and property retrieval using the OMEGA imaging spectrometer onboard Mars Express

Abstract

[1] Mapping of the aphelion clouds over the Tharsis plateau and retrieval of their particle size and visible opacity are made possible by the OMEGA imaging spectrometer aboard Mars Express. Observations cover the period from MY26 L s = 330 to MY29 L s = 180and are acquired at various local times, ranging from 8 AM to 6 PM. Cloud maps of the Tharsis region constructed using the 3.1 mm ice absorption band reveal the seasonal and diurnal evolution of aphelion clouds. Four distinct types of clouds are identified: morning hazes, topographically controlled hazes, cumulus clouds and thick hazes. The location and time of occurrence of these clouds are analyzed and their respective formation process is discussed. An inverse method for retrieving cloud particle size and opacity is then developed and can only be applied to thick hazes. The relative error of these measurements is less than 30% for cloud particle size and 20% for opacity. Two groups of particles can be distinguished. The first group is found over flat plains and is composed of relatively small particles, ranging in size from 2 to 3.5 mm. The second group is characterized by particle sizes of $5 mm which appear to be quite constant over L s and local time. It is found west of Ascraeus and Pavonis Mons, and near Lunae Planum. These regions are preferentially exposed to anabatic winds, which may control the formation of these particles and explain their distinct properties. The water ice column is equal to 2.9 pr.mm on average, and can reach 5.2 pr.mm in the thickest clouds of Tharsis.Citation: Madeleine, J. -B., et al. (2012), Aphelion water-ice cloud mapping and property retrieval using the OMEGA imaging spectrometer onboard Mars Express,

Characterisation of Martian dust aerosol phase function from sky radiance measurements by MSL engineering cameras

“…The resulting output parameters g 1 , g 2 and α varied in the order of 4%, 25% and 2%, respectively, with respect to the nominal scenario Sensitivity to presence of water-ice clouds. Part of the observations used in this study were obtained during the aphelion season (centred on L s ~ 70º) and the possible presence of water-ice clouds from the aphelion cloud belt, developing around L s = 40º -60º and dissipating near L s ~ 150º (e.g., Clancy et al, 1996Clancy et al, , 2003Madeleine et al, 2012) might introduce deviations in the dust phase function parameters retrieval. Although the majority of the observations were taken before 7h or after 16h (LTST), when detections of water-ice clouds are very low and the reported optical depth is almost negligible (Kloos et al, 2018), the sensitivity of the results to this phenomenon was evaluated.…”

The spiral troughs of Mars as cyclic steps

“…[95] We assume the size of ice particles is about 10 μm (a conservative estimate between the common size encountered in Martian water-ice clouds [Madeleine et al, 2012] and the fast-falling ice particles detected by Whiteway et al [2009]). We also assume that the extinction coefficient is~2.…”

Water in the Martian regolith from OMEGA/Mars Express

“…Water ice (as clouds in the atmosphere or as surface frost) significantly affects the radiance observed from orbit in the 3 μm spectral region [e.g., Vincendon et al, 2011;Madeleine et al, 2012]. As we aim to quantify the hydration of ice-free surfaces, the 1.5 μm band depth described in Langevin et al [2007] is used to detect icy frost presence at the surface and thick clouds in the atmosphere.…”