On the Non-uniformity of Water Vapor Abundance over the Polar Troughs on Mars: A case study

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) measures atmospheric gas abundances (H₂O, CO₂, CO) at visible and near infrared wavelengths. Retrieving water vapor abundances over the North Polar layered deposits (NPLD) is very challenging because of the presence of surface ice. Khayat el al. (2019), Icarus, 321, developed a new methodology, presented atmospheric water vapor maps over the north polar cap of Mars for 5+ Mars years, and provided insights into understanding the large-scale processes that control the water cycle over the polar cap during northern spring and summer. Images from the Thermal Emission Imaging System (THEMIS) onboard Mars Odyssey reveal the presence of clouds over geographic depressions, also known as the polar troughs, in the NPLD (Smith el al. (2013), JGR, 118). On small scales (few km), the combination of topography and katabatic wind leads to the formation of trough clouds in some occasions. With up to an order of magnitude enhancement in the spatial resolution over what exists currently (3 km), we present case studies of high-resolution (~ 320 m) water vapor column abundance retrievals over polar troughs with MRO/CRISM. A comprehensive list of high-spatial resolution retrievals of water vapor over the NPLD will open a window into understanding the small-scale processes driving the water sublimation from the polar cap during spring and summer.