Mars equatorial mesospheric clouds: Global occurrence and physical properties from Mars Global Surveyor Thermal Emission Spectrometer and Mars Orbiter Camera limb observations

Details Mars equatorial mesospheric clouds: Global occurrence and physical properties from Mars Global Surveyor Thermal Emission Spectrometer and Mars Orbiter Camera limb observations Mars equatorial mesospheric clouds: Global occurrence and physical properties from Mars Global Surveyor Thermal Emission Spectrometer and Mars Orbiter Camera limb observations

Apr 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007jgre..11204004c&link_type=abstract

Journal of Geophysical Research, Volume 112, Issue E4, CiteID E04004

Biology

17

Atmospheric Composition And Structure: Aerosols And Particles (0345, 4801, 4906), Atmospheric Composition And Structure: Planetary Atmospheres (5210, 5405, 5704), Planetary Sciences: Astrobiology: Planetary Atmospheres, Clouds, And Hazes (0343), Planetary Sciences: Solid Surface Planets: Atmospheres (0343, 1060), Planetary Sciences: Solar System Objects: Mars

Scientific paper

We report the occurrence of a new type of cloud in the Mars dayside (1300-1400 Local Time) atmosphere, apparent as high-altitude (60 to 80 km), vertically discrete aerosol scattering layers. Mars Global Surveyor (MGS) limb observations from the Thermal Emission Spectrometer (TES) visible channel indicate peak frequencies at the beginning and end of the aphelion northern summer season (L S = 30° and 150°), where they are confined to equatorial (15°S-15°N) latitudes and two longitude ranges (40°E-2°W and 50°W-120°W). Limb images from the MGS Mars Orbiter Camera (MOC) indicate significant horizontal variations in these Mars equatorial mesospheric (MEM) clouds on 20-50 km scales. On the basis of the distribution of projected limb heights, MEM clouds exhibit peak optical depths over 70-75 km altitudes, that are substantial (nadir τ vis of order 0.01) for the low-pressure region of formation (~1 μbar). Averaged TES limb infrared spectral (5-40 μm) and solarband radiance profiles corresponding to MEM occurrence indicate dust aerosols (r eff = 1.5-2.0 μm, τ vis ~ 0.4) at 0-25 km altitudes, capped by water ice clouds (r eff = 1.5-2.0 μm, τ vis ~ 0.2) at 20-45 km altitudes. The lack of detectable infrared radiances at MEM cloud heights precludes distinction of water versus CO2 ice, but indicates <=1 μm particle sizes for water or <=1.5 μm for CO2 ice compositions. More recent Mars Express observations point toward Mars mesospheric CO2 clouds, although current dynamical and radiative models do not indicate sufficiently cold temperatures at MEM cloud locations to produce daytime CO2 saturation conditions.

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