Martian mesospheric cloud observations by IUVS on MAVEN: Thermal tides coupled to the upper atmosphere

Abstract

We report observations of Martian mesospheric ice clouds and thermospheric scale heights by the Imaging Ultraviolet Spectrograph on NASA's Mars Atmosphere and Volatile Evolution mission. The clouds are observed between 6A.M. and 8A.M. local time using mid-UV limb observations between 60 and 80km tangent altitude where ice particles that scatter sunlight can appear as detached layers near the equator. The equatorial longitudinal distribution shows populations of clouds near -110 degrees E and -10 degrees E as well as a population near 90 degrees E, which does not have a clear precedent. The cloud populations indicate a wave 3 pattern near 70km, which is confirmed by independent mesospheric temperature observations. Scale heights 100km above the clouds derived from concurrent Imaging Ultraviolet Spectrograph (IUVS) observations also reveal a wave 3 longitudinal structure, suggesting that the temperature oscillations enabling the formation of mesospheric clouds couple to the upper atmosphere. Plain Language Summary The manuscript describes the observation of Martian mesospheric clouds between 60 and 80km altitude by the Imaging Ultraviolet Spectrograph (IUVS) on NASA's MAVEN spacecraft. The cloud observations are uniquely obtained at early morning local times, which complement previous observations obtained primarily later in the diurnal cycle. Differences in the geographic distribution of the clouds from IUVS observations indicate that the local time is crucial for the interpretation of mesospheric cloud formation. We also report concurrent observations of upper atmospheric scale heights near 170 km altitude, which are diagnostic of temperature. These observations suggest that the dynamics enabling the formation of mesospheric clouds propagate all the way to the upper atmosphere.