Diurnal Variations in the Aphelion Cloud Belt as Observed by the Emirates Exploration Imager (EXI)

Abstract

Observations by the Emirates eXploration Imager (EXI) on-board the Emirates Mars Mission are used to characterize the diurnal, seasonal, and spatial behavior of aphelion cloud belt during Mars Year 36 LS ∼ 30°–190°. Building from previous work with the Mars Color Imager (MARCI) onboard the Mars Reconnaissance Orbiter, we retrieve water ice extinction optical depth (τice) with an uncertainty ±0.0232 (excluding particle size effects). We connect EXI and MARCI using radiance and τice. Zonal and meridional diurnal trends are analyzed over 6–18 hr Local True Solar Time. The retrievals show large morning-evening asymmetries about a minimum near 12 hr. The latitudinal distributions in early morning are extensive and particularly striking near mid-summer. Comparisons to the Mars Planetary Climate Model show reasonable agreement with basic diurnal behavior, but noticeable departures include too much water ice in early morning, the general latitudinal extent, and behavior at smaller scales like the volcanoes and other topographically distinct features.