Seasonal Variations of Orographic Clouds on Mars with MRO/MARCI
observations and the LMD Mars Global Climate Model
∗ Anton

M. Fernandoa,b , Michael J. Wolffc,a and François Forgetd
for Atmospheric and Space Physics, Boulder, CO 80303, USA
b Space and Planetary Science Center, Khalifa University, Abu Dhabi, UAE
c Space Science Institution, Boulder, CO 80301, USA
d Laboratoire de Météorologie Dynamique/IPSL, Sorbonne Université, ENS,
PSL Research University, Ecole Polytechnique, CNRS, Paris, France
a Laboratory

Abstract
The formation of water ice clouds can significantly influence the Martian climate, although the Martian atmosphere contains low
water vapor concentrations compared to terrestrial levels. The lower Martian atmosphere
exhibits three types of global water ice cloud
systems: Aphelion cloud belt (ACB), polar
hoods (PHs) and orographic clouds. These
clouds are associated with topography, solar
heating, global atmospheric circulation, wave
activity and local convection. Although an
appreciable amount of research has been conducted on the first two regimes (ACB and
PHs) and very little attention has been given
to the third regime (orographic clouds). In
general, orographic clouds are observed in
northern spring and summer since they are
associated with the major Martian volcanoes.
Water ice optical depths provided by Mars
Color Imager (MARCI) of Mars Reconnaissance Orbiter (MRO) will be used to investigate seasonal variations of such clouds in
four volcanic regions: Alba Patera, Olympus Mons, Tharsis region and Elysium Mons.
The observed seasonal variations of water ice
clouds over volcanic regions are not well understood, and thus context will be provided
using the meteorological fields from LMDMGCM (Mars Global Climate Model led
by Laboratoire de Météorologie Dynamique
Paris, France).
Keywords:
Mars, water ice clouds,
MRO/MARCI, LMD-MGCM.

1

General Information

The MARCI is one of the instruments on NASA Mars
Reconnaissance Orbiter (MRO) and a wide-angle, low

resolution (1 - 10 km) imaging system which operates
in five visible and two ultraviolet (UV) bands. The
MARCI water ice cloud optical depth retrievals are obtained by the longer wavelength channel of the two
MARCI UV bands (Band 7 ∼ 320 nm) [5, 1]. The
MARCI provides daily global coverage from 13 to 14
south-to-north mapping swaths from a sun-synchronous
orbit. The center line of these swaths are separated by
∼ 27◦ in longitude and at local time near 15h00 true
solar time (LTST). The data were discarded for emergence angles greater than 70◦ and the downlinked pixel
field-of-view provides 8 km at nadir [5].
The LMD-MGCM takes dust loading of the atmosphere
into consideration, which is the main driver of the
Martian climate, and provides a series of dust scenarios: standard year (climatology), cold (low dust), warm
(dusty atmosphere) and dust storm [3, 4, 2]. Additionally, the LMD-MGCM provides “add-on" scenarios
that represent individual Martian years 24 to 34. The
LMD-MGCM does not provide water ice optical depths
and only offers water ice columns for Martian year scenarios. In this study, water ice columns provided by the
LMD-MGCM using the “standard year" dust scenario
(combining all “non-global dust storm” years MY 24 31) were converted into water ice optical depths using
1.6 µm as the average particle size to directly compare
with MARCI water ice optical depths.

2

MARCI water ice clouds

Figure 1 shows MARCI annual average water ice optical depths versus Ls of the major Martian volcanic regions for Martian years 28 - 33. In general, MARCI
water ice optical depths over Olympus Mons, Parvonis
Mons and Ascraeus Mons show similar features (one
peak around Ls = 100◦ ) in contrast to that of Alba Patera
and Arsia Mons. Arsia Mons exhibits clouds throughout the year and clouds in Alba Patera show two peaks
around Ls = 70◦ and Ls = 140◦ . Water ice clouds over
Elysium Mons also show two peaks, but the peak at Ls

= 70◦ is less prominent than the peak at Ls = 110◦ .

3

Method

Although, the MARCI/MRO has been operating since
the Martian year 28 and provides data for 7 continuous
Martian years, it only samples one local time (15h00
true solar time). Therefore, MARCI data are only suitable to study seasonal and inter-annual variations of
evening water ice clouds.
The boundaries of the volcanoes should be determined
in order to investigate seasonal variations of MARCI
water ice optical depths. Once the boundaries are established, an average water ice optical depth will be
calculated for each major volcanic region (Figure 1) to
identify the main seasonal features. Finally, these water ice optical depths will be compared with the meteorological outputs of the LMD Mars global climate
model and this comparison will reveal how local topography and meteorological variables are correlated with
the seasonal variations of water ice clouds in each volcanic region.

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Figure 1: Average water ice optical depths against Ls of the volcanic regions a) Alba Patera, b) Elysium Mons, c)
Olympus Mons, d) Arsia Mons, e) Ascraeus Mons and f) Parvonis Mons from MRO/MARCI for Martian years
28-33