The Key Influence of Mesoscale Gravity Waves in the Formation of Mesospheric CO2 Clouds on Mars

Details The Key Influence of Mesoscale Gravity Waves in the Formation of Mesospheric CO2 Clouds on Mars The Key Influence of Mesoscale Gravity Waves in the Formation of Mesospheric CO2 Clouds on Mars

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p51e..02s&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P51E-02

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[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [3329] Atmospheric Processes / Mesoscale Meteorology, [5445] Planetary Sciences: Solid Surface Planets / Meteorology, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Gravity waves [GW] are ubiquitous in the Martian low-density stable atmosphere. Of particular interest are the vertically-propagating GW emitted in the lowermost atmospheric levels. Those are expected to yield significant temperature disturbances in the rarefied upper Martian atmosphere [cf. aerobraking measurements]. To study those GW events, we designed dedicated idealized mesoscale simulations, featuring finer resolution both in horizontal and vertical dimensions compared to existing models. In the horizontal, our mesoscale model resolves at few kilometers resolution what is crudely parameterized in general circulation models [GCM]. In the vertical, our simulations employ a ``whole atmosphere" model from the surface of Mars to the upper thermosphere (130 km), which allow for GW to propagate from realistic tropospheric sources (incoming wind on a mountain) to mesospheric environments prone to complex radiative processes. We applied this novel high-resolution modeling of the Martian mesospheric circulations to high-altitude CO2 clouds, recently detected by Mars Global Surveyor and Mars Express. These structures remain a dynamical mystery for their vertical extent sometimes suggests convective processes. Their formation are not predicted by GCM, although coldest GCM temperatures (but not cold enough for CO2 to condensate) are found where and when clouds are observed. Our results quantitatively demonstrate that in such conditions GW amplification in the upper atmosphere can be so strong that mesoscale cold pockets would appear and permit the formation of CO2 clouds. Both the study of CO2 clouds and gravity waves are crucial to understand the Martian climate. Our model also offers a good basis for GW studies in other planetary environments (e.g., Venus). Perturbations of atmospheric temperature caused by vertical propagation of gravity waves. Simulations carried out at Ls = 0°, latitude = 0°, longitude = 0°, around local time 16:00, when mesospheric CO2 clouds have been observed at altitudes 70-80 km by the Mars Express / OMEGA spectrometer. Outputs from idealized mesoscale modeling (MM, full line) initialized with results from general circulation modeling (GCM, dashed line). While GCM computations do not predict conditions for CO2 condensation, high-resolution MM computations yield temperatures below CO2 condensation level (dotted lines) at altitudes where CO2 clouds have been observed.

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