Retrievals of dust and ozone from NOMAD-UVIS
Authors: Piccialli Arianna , Vandaele Ann Carine , Willame Yannick , Depiesse Cedric , Trompet Loic , Neary Lori , Viscardy Sebastien , Daerden Frank , Thomas Ian R. , Ristic Bojan , Mason Jon P. , Patel Manish , Bellucci Giancarlo , Lopez Moreno Jose Juan 
Published: March 2020

&lt;p&gt;We will present two years of observation of &lt;strong&gt;dust&lt;/strong&gt; and &lt;strong&gt;ozone&lt;/strong&gt; vertical distribution obtained from &lt;strong&gt;NOMAD-UVIS solar occultations&lt;/strong&gt;.&lt;/p&gt;&lt;p&gt;Atmospheric &lt;strong&gt;aerosols&lt;/strong&gt; are ubiquitous in the Martian atmosphere and they strongly affect the Martian climate [1]. This is particularly true during dust storms. In June 2018, after a pause of 11 years, a planet-encircling dust storm took place on Mars that lasted two months.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Ozone&lt;/strong&gt;, on the other hand, is a species with a short chemical lifetime and characterized by sharp gradients at the day-night terminator due to photolysis [2]. Odd hydrogen radicals play an important role in the destruction of ozone. This results in a strong anti-correlation between O&lt;sub&gt;3&lt;/sub&gt; and H&lt;sub&gt;2&lt;/sub&gt;O [2].&lt;/p&gt;&lt;p&gt;The &lt;strong&gt;NOMAD&lt;/strong&gt; (Nadir and Occultation for MArs Discovery) &amp;#8211; operating onboard the ExoMars 2016 Trace Gas Orbiter satellite &amp;#8211; started to acquire the first scientific measurements on 21 April 2018.&lt;/p&gt;&lt;p&gt;It is a spectrometer composed of 3 channels: 1) a solar occultation channel (SO) operating in the infrared (2.3-4.3 &amp;#956;m); 2) a second infrared channel LNO (2.3-3.8 &amp;#956;m) 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 [3,4]. The UVIS channel has a spectral resolution &lt;1.5 nm. In the solar occultation mode it is mainly devoted to study the climatology of ozone and aerosols content [5].&lt;/p&gt;&lt;p&gt;Since the beginning of operations, on 21 April 2018, NOMAD-UVIS acquired more than &lt;strong&gt;3000 solar occultations&lt;/strong&gt; with a complete coverage of the planet. NOMAD-UVIS spectra are simulated using the line-by-line radiative transfer code ASIMUT-ALVL developed at IASB-BIRA [6]. In a preliminary study based on SPICAM-UV solar occultations (see [7]), 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) [8,9].&lt;/p&gt;&lt;p&gt;NOMAD will help us improve our knowledge of the climatology of ozone and aerosols. In particular, we will have the rare opportunity to analyze the distribution of aerosols during a dust storm.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;[1] M&amp;#228;&amp;#228;tt&amp;#228;nen, A., Listowski, C., Montmessin, F., Maltagliati, L., Reberac, A., Joly, L., Bertaux, J.L., Apr. 2013. Icarus 223, 892&amp;#8211;941.&lt;/p&gt;&lt;p&gt;[2] Lef&amp;#232;vre, F., et al., Aug. 2008. Nature 454, 971&amp;#8211;975.&lt;/p&gt;&lt;p&gt;[3] Vandaele, A.C., et al., Planetary and Space Science, Vol. 119,&amp;#160; pp. 233&amp;#8211;249, 2015.&lt;/p&gt;&lt;p&gt;[4] Neefs, E., et al., Applied Optics, Vol. 54 (28),&amp;#160; pp. 8494-8520, 2015.&lt;/p&gt;&lt;p&gt;[5] M.R. Patel et al., In: Appl. Opt. 56.10 (2017), pp. 2771&amp;#8211;2782. DOI: 10.1364/AO.56.002771.&lt;/p&gt;&lt;p&gt;[6] Vandaele, A.C., et al., JGR, 2008. 113 doi:10.1029/2008JE003140.&lt;/p&gt;&lt;p&gt;[7] Piccialli, A., Icarus, in press, https://doi.org/10.1016/j.icarus.2019.113598.&lt;/p&gt;&lt;p&gt;[8] Neary, L., and F. Daerden (2018), Icarus, 300, 458&amp;#8211;476, doi:10.1016/j.icarus.2017.09.028.&lt;/p&gt;&lt;p&gt;[9] Daerden et al., 2019, Icarus 326, https://doi.org/10.1016/j.icarus.2019.02.030&lt;/p&gt;