CHARACTERIZATION OF THE MARTIAN MESOSPHERE BY LMD-MGCM
SIMULATIONS COMPARED TO NOMAD/TGO OBSERVATIONS.
F. González-Galindo, Instituto de Astrofı́sica de Andalucı́a-CSIC, Granada, Spain (ggalindo@iaa.es), M.A.
López-Valverde, A. Brines, A. Modak, A. Stolzenbach, B. Funke, J.J. López-Moreno, Instituto de Astrofı́sica
de Andalucı́a-CSIC, Granada, Spain, F. Forget, E. Millour, Laboratoire de Météorologie Dynamique, IPSL, Paris,
France, F. Lefèvre, M. Vals, F. Montmessin, LATMOS, Paris, France, M. Patel, Open University, Milton Keynes,
UK, G. Bellucci, Istituto di Astrofisica e Planetologia, Italy, A.C. Vandaele, BIRA, Brusels, Belgium.

Introduction
Since the beginning of the 21st century, many different
missions have provided unvaluable information about
the Martian atmosphere, including its seasonal and geographical variability. So, remote sounding by orbiters
such as Mars Global Surveyor and Mars Express allowed
for a good characterization of the dust, water and CO2
cycles in the lower atmosphere, as well as their effects
on the temperature structure (Smith, 2004; Montmessin
et al., 2017). In situ measurements by landers and rovers
have unveiled the meteorological structure near the surface of the planet (e.g. Savijarvi et al., 2019). The thermosphere/ionosphere region, as well as the magnetosphere and its interaction with the solar wind, have been
explored by Mars Express and specially the MAVEN
mission by a combination of remote sounding and insitu measurements (e.g. Bougher et al., 2017).
The Martian mesosphere, and in particular the upper mesosphere, above about 80 km from the surface,
remains poorly explored in comparison with the troposphere and the thermosphere/ionosphere. Remote
sounding by the Mars Climate Sounder instrument on
board Mars Reconnaissance Orbiter have allowed systematic measurements of the mesospheric temperature,
but only below 80 km (McCleesse et al., 2010). Stellar
occultations by SPICAM on Mars Express (Forget et al.,
2009) and IUVS on MAVEN (Gröller et al., 2018) have
provided CO2 density and temperature measurements
in the upper mesosphere, mostly on the night side, but
far from a complete coverage due to the limitations of
the stellar occultation technique. Observations of the
mesospheric CO2 clouds mostly by Mars Express and
MAVEN have been used to gain insight into the temperature and winds in the mesosphere (Määttänen et
al., 2010, González-Galindo et al., 2011). The analysis of UV atmospheric emissions by Mars Express and
IUVS/MAVEN has also supplied information about the
dynamical structure of the mesosphere (Gagné et al.,
2013, Schneider et al., 2020). Many of these observations have been interpreted thanks to the use of Global
Climate Models (GCMs, e.g. González-Galindo et al.,
2011). However, the scarcity of observations of the Martian mesosphere, and in particular of the composition and
temperature variability in the upper mesosphere, has not
allowed yet for a complete validation of the predictions

provided by GCMs.
Observations by the NOMAD and ACS instruments
on board the ExoMars Trace Gas Orbiter mission (TGO
in what follows) are starting to fill this gap by providing
measurements such as the abundance of mesospheric
water and the effects of global dust storms (Vandaele
et al., 2019; Belyaev et al., 2021; Brines et al., 2022),
the CO variability (Modak et al., 2022) or the temperature and density structure (López-Valverde et al., 2022).
For the first time we have a set of diverse atmospheric
parameters derived simultaneously with good vertical
resolution and from a single instrument, which is ideal
for model validation purposes.
In this work, we compare the predictions of the
LMD-Mars GCM (LMD-MGCM) in the mesosphere
with NOMAD observations, in order to validate the
model and to gain insight into the physical processes
at the origin of the observed structures.
IAA NOMAD datasets
The data used in this study haven been obtained by the
NOMAD instrument using the solar occultation (SO)
channel (and thus limited to the morning and evening terminators), and retrieved using the IAA retrieval scheme.
This scheme uses the radiative transfer model KOPRA
as a forward model and the Retrieval Control Program
(RCP) to invert the vertical profile. More details about
the IAA retrieval scheme can be found in López-Valverde
et al. (2022). When applied to different NOMAD
diffraction orders, the retrieval scheme provides measurements of the CO2 density and temperature profiles,
as well as profiles of CO and H2 O abundances. These
have been analyzed in López-Valverde et al. (2022),
Modak et al. (2022), and Brines et al. (2022), respectively, as well as in companion abstracts submitted to
this conference. In the near future, additional species
such as HDO will also be targeted.
LMD-MGCM
The LMD-MGCM version used in this study is the same
version used to build the Mars Climate Database v5.3,
including the formulations of the dust and water cycle

LMD-MGCM and NOMAD in the mesosphere
225

100

120

0.8
0.6

175
60

150

Altitude (km)

80
Temp (K)

Altitude (km)

1.0

100

200

80

40

0.4
0.2

60

0.0

−0.2

40
125

20
0
0

1.2

90

180
Ls

270

360

−0.4
−0.6

20

100

0
−90

log10(CO/CO2 (%))

120

−0.8
−1.0
−60

−30

0
Latitude

30

60

90

Figure 1: Seasonal variation of the temperature profiles predicted by the LMD-MGCM during MY34, at the morning terminator and a constant latitude of 45N

Figure 2: Latitudinal variation of the CO/CO2 ratio profiles
predicted by the LMD-MGCM at the morning terminator for
Ls=180 and MY34

described in Navarro et al. (2014) and thermospheric
processes described in González-Galindo et al. (2015).
We have performed simulations appropriate for Mars
Years (MY) 34 and 35, using the observed dust abundance in the lower atmosphere given by Montabone et
al. (2020) and the UV solar variability using the scheme
described in González-Galindo et al. (2015).
We analyze the LMD-MGCM predictions in two different ways. First, for a direct one-to-one comparison
with NOMAD measurements, the GCM results are extracted at the exact location and time of each of the
NOMAD observations. Second, in order to provide a
more general view of the atmospheric behavior at the
terminators not limited to the NOMAD temporal and
geographical coverage, a post-processing software developed at the LMD has been used to extract the model
predictions at a fixed value of Solar Zenith Angle of 90
degrees, both in the morning and the evening terminators, at all latitudes and seasons.

able the temperature peak predicted by the model at an
altitude of around 80 km during the second half of the
year.
While the starting phase of the MY34 GDS is not
well covered by NOMAD observations, the retrieved
temperature profiles show a maximum of temperature
at around Ls =220, in agreement with the prediction of
the model, as well as a temperature increase at the end
of the year (López-Valverde et al., 2022). Interestingly,
a temperature peak at around 80 km is also observed
by NOMAD, although its seasonal extension seems to
be more limited than in the simulations. However, a
detailed comparison shows that the LMD-MGCM systematically overestimates the temperatures in the layers
above 50 km (López-Valverde et al., 2022), suggesting
deficiencies in the description of the radiative heating
terms in the model and/or in the representation of tides
or other dynamical processes affecting the temperature
structure.
Regarding the CO2 density, the strong seasonal variations observed by NOMAD are rather well captured by
the model.

Results
CO2 density and temperature
Fig. 1 shows the variation with altitude and season of the
temperature predicted by the LMD-MGCM in the morning terminator and in the mid latitudes of the Northern
hemisphere for MY34. The effect of the global dust
storm (GDS) starting shortly after Ls =180 in MY34 is
clearly seen, producing an increase of temperature that
is felt from the lower atmosphere to the top of the mesosphere. Note also the temperature increase produced by
the regional dust storm around Ls =330. It is also notice-

CO
Fig. 2 shows the latitudinal variation of the predicted
CO abundance profiles during the equinox season. The
CO mixing ratio increases with altitude, reaching values
larger than 1% in the upper mesospheric layers, due to
the effects of CO2 photolysis producing CO in the upper
layers, as well as the molecular diffusion of CO enhancing its abundance relative to CO2 above the homopause.
A clear enhancement of the CO relative abundance

LMD-MGCM and NOMAD in the mesosphere
90

150

60

120
90

0
60

H2O (ppm)

Latitude

30

On the perihelion season of MY35, on the other
hand, the comparison of the mesospheric water abundance between NOMAD observations and the LMDMGCM is quite good (Brines et al., 2022). This suggests
that the overestimation during MY34 is probably caused
by a misrepresentation of the vertical dust structure in
the model during the MY34 GDS. A similar conclusion
was obtained from the comparison of the LMD-MGCM
water abundances with ACS observations (Vals et al.,
2022).

−30
30

−60
−900

Acknowledgments
0
90

180

270

360
Ls

450

540

630

720

Figure 3: Seasonal and Latitudinal variation of the H2 O mixing ratio predicted by the LMD-MGCM at a constant altitude level of 60km, for the morning terminator and for MY34
(Ls =0-360) and MY35 (Ls =360-720

is predicted at both poles. This is the consequence of
the structure of the meridional circulation at the equinox
season, characterized by two symmetric Hadley cells
transporting matter from the equator to both poles. This
latitudinal variation of the CO abundance is supported by
NOMAD observations, which show a similar enhancement in the high latitude regions during the equinox
season (Modak et al., 2022).
A quantitative comparison with the CO abundances
observed by NOMAD shows that the model tends to
underestimate globally the CO relative abundance.
H2 O
Fig. 3 shows the latitudinal and seasonal variation of the
H2 O relative abundance predicted by the LMD-MGCM
in the morning terminator at a constant altitude of 60
km during both MY34 and MY35. It can be seen that
during the aphelion season the water abundance is quite
low, below a few ppms. The abundance increases in
the perihelion seasons, reaching abundances of about 50
ppms for MY35. In MY34 the effect of the GDS is very
clear, producing water abundances above 150 ppm.
Similarly, NOMAD observations show a strong increase of the mesospheric water abundance following
the MY34 GDS, although observed values at 60 km exceed 200 ppm (Brines et al., 2022), larger than predicted
by the model. An important difference is that the decay of the water abundance after the storm is stronger
and faster in the observations than in the model prediction, so that the model significantly overestimates the
mesospheric abundance until Ls =270.

F.G-G. is funded by the Spanish Ministerio de Ciencia, Innovación y Universidades, the Agencia Estatal
de Investigación and EC FEDER funds under project
RTI2018-100920-J-I00. MALV, AB, AM, and AS were
supported by grant PGC2018-101836-B-100 (MCIU /
AEI / FEDER, EU). The IAA team acknowledges financial support from the State Agency for Research of
the Spanish MCIU through the “Center of Excellence
Severo Ochoa" award to the Instituto de Astrofı́sica de
Andalucı́a (SEV-2017-0709)

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