EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Impact of gradients at the Martian terminator on the retrieval of ozone from TGO/NOMAD-UVIS

Arianna Piccialli1, Ann Carine Vandaele1, Lori Neary1, Yannick Willame1, Shohei Aoki2, Loic Trompet1, Cedric Depiesse1, Sebastian Viscardy1, Frank Daerden1, Justin Erwin1, Ian R. Thomas1, Bojan Ristic1, Jon P. Mason3, Manish Patel3, Alain Khayat4, Mike Wolff5, Giancarlo Bellucci6, and Jose Juan Lopez-Moreno7
Arianna Piccialli et al.
  • 1Belgian Institute for Space Aeronomy (BIRA-IASB), Planetary Atmospheres, Uccle, Brussels, Belgium (
  • 2Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA)
  • 3Open University, UK,
  • 4NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
  • 5Space Science Institute, Boulder, Colorado, USA
  • 6INAF, Istituto di Astrofisica e Planetologia Spaziali, Italy
  • 7IAA/CSIC, Granada, Spain

We will investigate the impact of day-night temperature and compositional gradients at the Martian terminator on the retrieval of vertical profiles of ozone obtained from NOMAD-UVIS solar occultations

Rapid variations in species concentration at the terminator have the potential to cause asymmetries in the species distributions along the line of sight of a solar occultation experiment. Ozone, in particular, displays steep gradients across the terminator of Mars due to photolysis [1]. Nowadays, most of the retrieval algorithms for solar and stellar occultations rely on the assumption of a spherically symmetrical atmosphere. However, photo-chemically induced variations near sunrise/sunset conditions need to be taken into account in the retrieval process in order to prevent inaccuracies.

NOMAD (Nadir and Occultation for MArs Discovery) is a spectrometer composed of 3 channels: 1) a solar occultation channel (SO) operating in the infrared (2.3-4.3 μm); 2) a second infrared channel LNO (2.3-3.8 μm) capable of doing nadir, as well as solar occultation and limb; and 3) an ultraviolet/visible channel UVIS (200-650 nm) that can work in the three observation modes [2,3]. 

The UVIS channel has a spectral resolution <1.5 nm. In the solar occultation mode, it is mainly devoted to study the climatology of ozone and aerosols [4,5,6].

Since the beginning of operations, on 21 April 2018, NOMAD-UVIS acquired more than 8000 solar occultations with an almost complete coverage of the planet.

NOMAD-UVIS spectra are simulated using the line-by-line radiative transfer code ASIMUT-ALVL developed at IASB-BIRA [7]. In a preliminary study based on SPICAM-UV solar occultations (see [8]), ASIMUT was modified to take into account the atmospheric composition and structure at the day-night terminator. As input for ASIMUT, we used gradients predicted by the 3D GEM-Mars v4 Global Circulation Model (GCM) [9,10]. 

[1] Lefèvre, F., Bertaux, J.L., Clancy, R. T., Encrenaz, T., Fast, K., Forget, F., Lebonnois, S., Montmessin, F., Perrier, S., Aug. 2008. Heterogeneous chemistry in the atmosphere of Mars. Nature 454, 971–975.
[2] Vandaele, A.C., et al., Planetary and Space Science, Vol. 119, pp. 233–249, 2015. 
[3] Neefs, E., et al., Applied Optics, Vol. 54 (28), pp. 8494-8520, 2015.
[4] M.R. Patel et al., In: Appl. Opt. 56.10 (2017), pp. 2771–2782. DOI: 10.1364/AO.56.002771. 
[5] M.R. Patel et al., In: JGR (Planets), Vol. 126, Is. 11, 2021.
[6] Khayat, Alain S. J., et al., In: JGR (Planets), Vol. 126, Is. 11, 2021.
[7] Vandaele, A.C., et al., JGR, 2008. 113 doi:10.1029/2008JE003140.
[8] Piccialli, A., Icarus, submitted.
[9] Neary, L., and F. Daerden (2018), Icarus, 300, 458–476, doi:10.1016/j.icarus.2017.09.028.
[10] Daerden et al., 2019, Icarus 326,

How to cite: Piccialli, A., Vandaele, A. C., Neary, L., Willame, Y., Aoki, S., Trompet, L., Depiesse, C., Viscardy, S., Daerden, F., Erwin, J., Thomas, I. R., Ristic, B., Mason, J. P., Patel, M., Khayat, A., Wolff, M., Bellucci, G., and Lopez-Moreno, J. J.: Impact of gradients at the Martian terminator on the retrieval of ozone from TGO/NOMAD-UVIS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12125,, 2022.