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
L$_S$$\sim$30$^\circ$-190$^\circ$.
Building from previously work with the Mars Color Imager (MARCI) onboard
the Mars Reconnaissance Orbiter, we retrieve water ice extinction
optical depth ($\tau_{ice}$) with an uncertainty
$\pm$0.022 (excluding particle size effects). We
connect EXI and MARCI using radiance and
$\tau_{ice}$. Zonal and meridional diurnal trends
are analyzed over 6h-18h Local True Solar Time. The retrievals show
large morning-evening asymmetries about a minimum near 12h. 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 the basic diurnal behavior,
but noticeable departures include too much water ice in early morning,
the general latitudinal extent, and behavior smaller scales like the
volcanoes and other topographically distinct features.