Role of Thermal Tides and Gravity Waves in Mars Equatorial Mesospheric Cloud Formation Revealed by Mars Climate Sounder Observations

Abstract

Mesospheric CO2-ice clouds form in one of the coldest regions of Mars's atmosphere, but to date links between the broader thermal structure, dynamical phenomena, and the global and seasonal structure of mesospheric clouds have been tentative due to a limited sample of cloud observations. Combining a comprehensive set of cloud identifications and temperature observations from the Mars Climate Sounder onboard the Mars Reconnaissance Orbiter, we demonstrate for the first time that the spatial distribution and seasonal evolution—including the well-known yet unexplained solstitial pause—of the aphelion mesospheric cloud population are governed by the interplay of thermal tides and gravity waves. In addition, we present the first investigation of the nighttime cloud distribution and our approach successfully explains the observed day-to-night differences. The significant day-to-night variability in observed cloud occurrence rates and likelihoods of subcondensation temperatures point toward larger nighttime particle sizes possibly due to more favorable growth conditions.