Thermal Forcing of the Nocturnal Near Surface Environment by Martian Water Ice Clouds

We explore the potential role of clouds in moderating the nighttime temperature within Gale crater, as observed by the Rover Environmental Monitoring Station (REMS) instrument suite aboard the Curiosity rover. Just prior to aphelion, the decreasing trend in minimum daily temperature within Gale slows down. We investigate if this is due to increased formation of twilight and nighttime clouds, re‐radiating heat and reducing atmospheric and surface cooling. While diurnal analysis of REMS temperatures shows brief atmospheric warmings of 3–5 K post‐sunset during the occurrence of these clouds, an absence of similar warmings in the ground temperature measurements make it unlikely that clouds are the primary source. Seasonally, however, clouds that persist overnight could cause a warming of daily minimum surface temperatures in the Ls∼20°–50° season. This period can serve as a baseline and allow the potential effects of clouds to be more clearly discerned in the REMS temperature measurements. For this season, and in the peak of the aphelion cloud belt season, our modeled atmospheric energy budget shows a nocturnal decay signature of downward IR reflected and re‐emitted flux consistent with the presence and impact of clouds. The expected approximate exponential decay of this flux post‐sunset is damped more heavily in cloudier seasons than less cloudy or dusty seasons, suggesting formation and thickening of ice clouds as atmospheric nighttime temperatures cool. At Gale crater on Mars, we expect temperatures to be coldest at aphelion, the time when Mars is furthest from the Sun. Interestingly, we find that in some years, the lowest nighttime surface temperatures do not steadily decline during the period approaching aphelion but, rather, show a short‐lived reversal of this trend, becoming slightly warmer for a few weeks prior to aphelion. Analysis of surface and air temperature data from the Curiosity rover during this period, along with twilight imagery from the surface, and infrared measurements from orbit, points to the possibility of nighttime clouds acting as a means of warming the surface. These clouds only form around aphelion, perhaps explaining the unusual seasonal temperatures during this period. Nighttime warmings of the atmosphere and surface are detected and hypothesized as thermal signatures of cloudsThe range of areocentric longitudes where the warmings are observed coincides with the visual observation of cloudsAn energy balance model shows consistency with nocturnal evolution of reflected and re‐emitted radiation from clouds Nighttime warmings of the atmosphere and surface are detected and hypothesized as thermal signatures of clouds The range of areocentric longitudes where the warmings are observed coincides with the visual observation of clouds An energy balance model shows consistency with nocturnal evolution of reflected and re‐emitted radiation from clouds