MESOSPHERIC CARBON DIOXIDE AND TEMPERATURE RETRIEVALS
FROM NOMAD-SO ONBOARD TGO.
L. Trompet, A.C. Vandaele, I. Thomas Royal Belgian Institute for Space Aeronomy, Brussels, Belgium
(loic.trompet@aeronomie.be), S. Aoki Graduate School of Frontier Sciences, The University of Tokyo,
Kashiwa, Japan, F. Daerden, J. Erwin, Z. Flimon, A. Mahieux, L. Neary, S. Robert Royal Belgian Institute
for Space Aeronomy, Brussels, Belgium, G. Villanueva, G. Liuzzi Goddard Flight Space Center, GFSC,
Greenbelt, USA, M.A. Lopez-Valverde, A. Brines, J. J. Lopez-Moreno Instituto de Astrofisica de Andalucia,
IAA/CSIC, Spain, G. Bellucci Istituto di Astrofisica e Planetologia Spaziali, IAPS/INAF, Rome, Italy, M. R.
Patel 8School of Physical Sciences, The Open University, Milton Keynes, UK.

Introduction:
Mars mesosphere is the place of many atmospheric phenomena such as gravity waves, large amplitudes tides and temperature inversion. The mesosphere has been less studied than the lowest and
highest altitudes but NOMAD-SO (SO in the following) is regularly scanning the Mars atmosphere from
the troposphere to an altitude around 200 km and we
focus in this work on the retrievals in the mesosphere.
The SO channel of the NOMAD instrument
(Vandaele et al., 2015) is dedicated to solar occultation measurements and the derived profiles are located at the terminator. SO is an infrared spectrometer
(2.3-4.3 µm) composed of an echelle grating with an
acousto-optical tunable filter for diffraction order
selection. In this work, we focus on the retrievals
from diffraction order 148 which is centered on the
CO2 fundamental band 21102-00001 (AFGL code)
and covers the spectral range 3325.6 cm-1 to
3351.9 cm-1. We derived 963 profiles from the full
Martian years (MY) 35 and from MY 36 until a solar
longitude (Ls) of 135° (23/03/2019 till 01/12/2021).
The latitude covered by this dataset are located mainly around 60° North and 60° South with still some
profiles located closer to the equator (see Figure 2,
the blue points represent all measurements for this
dataset).
Method:
The retrieval method is split into three main
steps. First, slant columns are inverted for each SO
spectrum individually with the ASIMUT radiative
transfer code (Vandaele et al., 2006) based on the
optimal estimation method (Rodgers, 2000). The
highest altitude bound is limited by the strength of
the CO2 lines and the lowest one by the saturation of
the CO2 lines.
The second step is the vertical inversion. The
slant column profile is converted into a vertical density profile with an iterated Tikhonov method
(Quémerais et al., 2006). This method requires
providing a regularization parameter. With a synthetic example, we tested 7 methods to infer the best
regularization method and the best one appears to be
the expected error estimation (Doicu et al., 2010; Xu
et al., 2016).

In the third step, we derive the pressure and temperature profiles with the hydrostatic equilibrium
equation (Mahieux, 2011; Snowden et al., 2013).
This step is usually performed numerically but we
derived an analytical formula that makes the error
computation easier. The uncertainties are on average
10 K at 0.02 Pa (around 90 km) and 2 K at 0.4 Pa
(around 60 km).
Results:
Figure 1 shows the retrieved carbon dioxide density values at 75 km. As expected, we see lower values near aphelion and highest values close to perihelion. We also see that, closer to aphelion, the values
in the Southern hemisphere are lower than in the
Northern hemisphere. The inverse happens closer to
perihelion.

Figure 1: Carbon dioxide density at 75 km retrieved
from NOMAD-SO during MY 35 and the beginning of
MY 36.

The temperature profiles show several warm layers mainly appearing at dawn in both hemispheres
and dusk in the Northern hemisphere while they are
more homogeneous at Southern dusks between Ls
50° and 150°. The location of the warm layers at the
beginning of MY 35 and 36 are very similar.
We compare our results with MRO-MCS (Zurek
& Smrekar, 2007; Kleinböhl et al., 2009) co-located
profiles. They are in good agreement with an average
difference of 3 K. The main differences can be
explained by a difference in location.
We also compared our results to those of the GEMMars GCM (Neary & Daerden, 2018; Daerden et al.,
2019, 2022) interpolated for the location of SO profiles. The profiles agree well except for the presence
in SO profiles of a colder layer in the Southern hemisphere for the beginning of the year (until Ls 60°), a
warmer layer at Ls 300° to 360° and a warm layer at
dawn in the Northern hemisphere for Ls 240° to

360°.
Figure 1 shows some examples of SO temperature profiles that have very close latitude, local time
and Ls but different longitudes. The upper panel contains profiles at dawn and the lower panel contains
profiles at dusk. We see more variability and even
some strong temperature inversion between 55 and
70 km for the profiles at dawn and more monotonic
profiles at dusk.

Figure1: Two examples of SO temperature profiles.
The locations are given above the panels. Panel b for dawn
and panel d for dusk.

To the temperature, we fitted the formula
(
− ) where k is the wavenumber (1, 2, 3 or 4), is
the longitude, A is the amplitude and φ is the phase.
In the case at dawn (panel a), we derived a wavenumber-1 component with an amplitude of 10% of
the background temperature and with still a remaining wavenumber-3 component of 5%.
We also checked the presence of a strong warm
layer with a method similar to Nakagawa et al.
(2020). Their presence is given in orange and green
in Figure 2. The warm layers are present in 20% of
the dataset, mainly in the morning around 9 h and in
the Southern hemisphere for the first half-year and in
the Northern hemisphere in the second half-year.

Figure2: In blue: location of all profiles for diffraction
order 148 in MY35 and 36 until Ls 135°. In orange: location of profiles with a warm layer. In green: location of
profiles with two warm layer.

We also report that amongst the 963 profiles, six
of them contain some values lower than the temperature limit for CO2 condensation. Those profiles are
presented in Figure 3. Two of them were already
reported in Liuzzi et al. (2021). Those six profiles
are located at places where CO2 ice clouds were already reported except for the one at Ls 213° (red in
Figure 3).

Excellence Severo Ochoa’ award for the Instituto de
Astrofísica de Andalucía (SEV-2017-0709) and funding
by grant PGC2018-101836-B-100 (MCIU/AEI/FEDER,
EU). US investigators were supported by the National
Aeronautics and Space Administration. Canadian investigators were supported by the Canadian Space Agency.

Figure 3: Six temperature profiles with a value lower
than the temperature limit for CO2 condensation.

Conclusions:
We derived 963 CO2 and temperature profiles of
the mesosphere of Mars. Many of those temperature
profiles contain specific features. The temperature
profiles retrieved for the beginning of MY35 and
MY36 show the same latitudinal trends. The seasonal
variations show similar behavior to previous studies
and simulations (see for instance, Forget et al., 2009;
González-Galindo et al., 2011). Some clear longitudinal trends are visible in the profiles at high latitudes around 60°. We derived the longitudinal components. Some strong warm layers were already reported on the night side and we report their presence
as well at the terminator in 20% of the profiles. We
also report the presence of six temperature profiles
with a temperature lower than the temperature limit
for CO2 condensation. Those results have been submitted in two papers (Trompet et al., 2022; Trompet,
et al., 2022) and another analysis on MY34 Ls 160 to
360° has been submitted in (Lopez-Valverde et al.,
2022)
Acknowledgement:
The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by CoPI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and
the United Kingdom (Open University). This project
acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401,
4000121493), by the Spanish Ministry of Science and
Innovation (MCIU), and by European funds under grants
PGC2018-101836-B-I00 and ESP2017-87143-R
(MINECO/FEDER), as well as by UK Space Agency
through grants ST/V002295/1, ST/V005332/1, and
ST/S00145X/1 and Italian Space Agency through grant
2018-2-HH.0. This work was supported by the Belgian
Fonds de la Recherche Scientifique – FNRS under grant
number 30442502 (ET_HOME). This project has received
funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No
101004052 (RoadMap project). The IAA/CSIC team
acknowledges financial support from the State Agency for
Research of the Spanish MCIU through the ‘Center of

References:
Daerden, F., Neary, L., Villanueva, G., Liuzzi, G., Aoki,
S., Clancy, R. T., Whiteway, J. A., Sandor, B. J.,
Smith, M. D., Wolff, M. J., Pankine, A., Khayat, A.,
Novak, R., Cantor, B., Crismani, M., Mumma, M.
J., Viscardy, S., Erwin, J., Depiesse, C., …
Vandaele, A. C. (2022). Explaining NOMAD D/H
Observations by Cloud-induced Fractionation of
Water Vapor on Mars. Journal of Geophysical
Research: Planets, 127(2), e2021JE007079.
https://doi.org/10.1029/2021JE007079
Daerden, F., Neary, L., Viscardy, S., García Muñoz, A.,
Clancy, R. T., Smith, M. D., Encrenaz, T., &
Fedorova, A. (2019). Mars atmospheric chemistry
simulations with the GEM-Mars general circulation
model. Icarus, 326, 197–224.
https://doi.org/10.1016/j.icarus.2019.02.030
Doicu, A., Trautmann, T., & Schreier, F. (2010).
Numerical Regularization for Atmospheric Inverse
Problems. In Numerical Regularization for
Atmospheric Inverse Problems. Springer Berlin
Heidelberg. https://doi.org/10.1007/978-3-64205439-6
Forget, F., Montmessin, F., Bertaux, J. L., GonzálezGalindo, F., Lebonnois, S., Quémerais, E., Reberac,
A., Dimarellis, E., & López-Valverde, M. A.
(2009). Density and temperatures of the upper
Martian atmosphere measured by stellar
occultations with Mars Express SPICAM. Journal
of Geophysical Research E: Planets, 114(1), 1004.
https://doi.org/10.1029/2008JE003086
González-Galindo, F., Määttänen, A., Forget, F., & Spiga,
A. (2011). The martian mesosphere as revealed by
CO2 cloud observations and General Circulation
Modeling. Icarus, 216(1), 10–22.
https://doi.org/10.1016/J.ICARUS.2011.08.006
Kleinböhl, A., Schofield, J. T., Kass, D. M., Abdou, W.
A., Backus, C. R., Sen, B., Shirley, J. H., Lawson,
W. G., Richardson, M. I., Taylor, F. W., Teanby, N.
A., & McCleese, D. J. (2009). Mars Climate
Sounder limb profile retrieval of atmospheric
temperature, pressure, and dust and water ice
opacity. Journal of Geophysical Research E:
Planets, 114(10), 1–30.
https://doi.org/10.1029/2009JE003358
Liuzzi, G., Villanueva, G. L., Trompet, L., Crismani, M.
M. J., Piccialli, A., Aoki, S., Lopez‐ Valverde, M.
A., Stolzenbach, A., Daerden, F., Neary, L., Smith,
M. D., Patel, M. R., Lewis, S. R., Clancy, R. T.,
Thomas, I. R., Ristic, B., Bellucci, G.,
Lopez‐ Moreno, J., & Vandaele, A. C. (2021). First
Detection and Thermal Characterization of
Terminator CO 2 Ice Clouds with
ExoMars/NOMAD. Geophysical Research Letters,
48(22), e2021GL095895.
https://doi.org/10.1029/2021gl095895
Lopez-Valverde, M.-A., Funke, B., Brines, A.,
Stolzenbach, A., Modak, A., Hill, B., Francisco, G.G., Thomas, I., Trompet, L., Aoki, S., Villanueva,

G., Liuzzi, G., Erwin, J., Vandaele, A.-C.,
Grabowski, U., Forget, F., Moreno, J. J. L.,
Rodriguez, J., Ristic, B., … Patel, M. (2022).
Martian atmospheric temperature and density
profiles during the 1st year of NOMAD/TGO solar
occultation measurements. Journal of Geophysical
Research: Planets, Submitted.
Mahieux, A. (2011). Inversion of the infrared spectra
recorded by the SOIR instrument on board
VenusExpress [Université Libre de Bruxelles].
http://planetary.aeronomie.be/multimedia/pdf/These
_ArnaudMahieux_2011.pdf
Nakagawa, H., Jain, S. K., Schneider, N. M., Montmessin,
F., Yelle, R. V., Jiang, F., Verdier, L., Kuroda, T.,
Yoshida, N., Fujiwara, H., Imamura, T., Terada, N.,
Terada, K., Seki, K., Gröller, H., & Deighan, J. I.
(2020). A Warm Layer in the Nightside Mesosphere
of Mars. Geophysical Research Letters, 47(4), 1–
10. https://doi.org/10.1029/2019GL085646
Neary, L., & Daerden, F. (2018). The GEM-Mars general
circulation model for Mars: Description and
evaluation. Icarus, 300, 458–476.
https://doi.org/10.1016/j.icarus.2017.09.028
Quémerais, E., Bertaux, J. L., Korablev, O., Dimarellis, E.,
Cot, C., Sandel, B. R., & Fussen, D. (2006). Stellar
occultations observed by SPICAM on Mars
Express. Journal of Geophysical Research E:
Planets, 111(9), 9–13.
https://doi.org/10.1029/2005JE002604
Rodgers, C. D. (2000). Inverse methods for atmospheric
sounding (Vol. 2). WORLD SCIENTIFIC.
https://doi.org/10.1142/3171
Snowden, D., Yelle, R. V., Cui, J., Wahlund, J.-E. E.,
Edberg, N. J. T. T., & Ågren, K. (2013). The
thermal structure of titan’s upper atmosphere, I:
Temperature profiles from Cassini INMS
observations. Icarus, 226(1), 552–582.
https://doi.org/10.1029/2010JA016251
Trompet, L., Vandaele, A. C., Thomas, I., Aoki, S.,
Daerden, F., Erwin, J., Flimon, Z., Mahieux, A.,
Neary, L., Robert, S., Villanueva, G., G. Liuzzi, 6,
Lopez-Valverde, M. A., Brines, A., Bellucci, G.,
Lopez-Moreno, J. J., & Patel, M. R. (2022). Carbon
dioxide retrievals from NOMAD-SO on ESA’s
ExoMars Trace Gas Orbiter and temperature
profiles retrievals with the hydrostatic equilibrium
equation. II. Temperature variabilities in the
mesosphere at Mars terminator. Journal of
Geophysical Research: Planets, Submitted.
Trompet, L., Vandaele, A. C., Thomas, I., Aoki, S.,
Daerden, F., Erwin, J., Flimon, Z., Mahieux, A.,
Neary, L., Robert, S., Villanueva, G., Liuzzi, G.,
Lopez-Valverde, M. A., Brines, A., Bellucci, G.,
Lopez-Moreno, J. J., & Patel, M. R. (2022). Carbon
dioxide retrievals from NOMAD-SO on ESA’s
ExoMars Trace Gas Orbiter and temperature
profiles retrievals with the hydrostatic equilibrium
equation. I. Description of the method. Journal of
Geophysical Research: Planets, Submitted.
Vandaele, A. C., Kruglanski, M., & De Mazière, M.
(2006). Modeling and retrieval of atmospheric
spectra using ASIMUT. European Space Agency,
(Special Publication) ESA SP, 618.
Vandaele, A. C., Neefs, E., Drummond, R., Thomas, I. R.
R., Daerden, F., Lopez-Moreno, J.-J. J., Rodriguez,
J., Patel, M. R. R., Bellucci, G., Allen, M., Altieri,

F., Bolsée, D., Clancy, T., Delanoye, S., Depiesse,
C., Cloutis, E., Fedorova, A., Formisano, V., Funke,
B., … Wolff, M. (2015). Science objectives and
performances of NOMAD, a spectrometer suite for
the ExoMars TGO mission. Planetary and Space
Science, 119, 233–249.
https://doi.org/10.1016/j.pss.2015.10.003
Xu, J., Schreier, F., Doicu, A., & Trautmann, T. (2016).
Assessment of Tikhonov-type regularization
methods for solving atmospheric inverse problems.
Journal of Quantitative Spectroscopy and Radiative
Transfer, 184, 274–286.
https://doi.org/10.1016/j.jqsrt.2016.08.003
Zurek, R. W., & Smrekar, S. E. (2007). An overview of
the Mars Reconnaissance Orbiter (MRO) science
mission. In Journal of Geophysical Research E:
Planets (Vol. 112, Issue 5, pp. 5–6). John Wiley &
Sons, Ltd. https://doi.org/10.1029/2006JE002701