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Temperature Variability in Mars Mesosphere and Local Solar Time

Presentation #307.08 in the session Characterizing the Martian Atmosphere, All the Way Up (Oral Presentation)

Published onOct 23, 2023
Temperature Variability in Mars Mesosphere and Local Solar Time

Current missions to Mars have reinvigorated investigations of the middle and upper atmosphere. Solar occultation measurements yield high precision determinations of temperature profiles by virtue of the well determined tangent height and the spectral opacity of specific constituents. Such measurements are restricted to the dawn and dusk terminators, which is a significant limitation in a CO2-rich atmosphere that is infrared-active and thus undergoes substantial temperature changes throughout the sol at all altitudes. A different way to probe temperature in Mars mesosphere uses the non-local thermodynamic equilibrium (non-LTE) emission of CO2, measuring temperature through Maxwellian broadening of carbon dioxide lines at 10.6 micron wavelength using the Goddard Space Flight Center Heterodyne Instrument for Planetary Winds and Composition (HIPWAC) at resolving power 30 million. Observations in April 2016 from the NASA Infrared Telescope Facility (IRTF) measured temperatures in the equatorial mesosphere that varied between a maximum of about 140K to minimum temperatures less than 90K, determined for locations at local solar time from mid-morning to near dusk. The non-LTE line appears as a narrow emission core within a broad absorption formed by tropospheric CO2, which provides temperature information reaching down to the martian surface, while the mesospheric line probes temperature at about 60-80 km altitude. We will report on the spatial distribution of temperature and emission line strength with local solar time on Mars. These remote measurements complement results from orbital spacecraft through access to a broad range of local solar time.

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