The Ultraviolet and Visible spectrometer (UVIS)[1], is the ultraviolet and visible channel of the NOMAD spectrometer[2] onboard the ExoMars Trace Gas Orbiter (TGO). UVIS has been in orbit around mars for over two years with near continuous nadir observations through the latter half of MY34, through to MY36.
A retrieval procedure was developed to obtain the ozone and aerosol column abundances in the martian atmosphere. The radiative transfer is performed using the discrete ordinates DISORT package developed by Knut Stamnes and collaborators[3] and the ‘front-end’ routines (DISORT_MULTI) developed by Mike Wolff, for studies of the martian atmosphere [4,5,6].

Seasonally the ozone distribution is consistent, with low ozone abundances in equatorial regions and higher ozone abundances at higher latitudes in the winter season. As the martian atmosphere cools through northern spring, from the reduced solar insolation, we observed a steady increase in equatorial ozone. UVIS observations show significant ozone entrapment in large impact basins, such as Hellas Basin[6]. Ozone abundances measured within Hellas can be 10-20 µm-atm, compared to 2-5 µm-atm outside the crater.

A global dust storm was observed in MY34 which started around solar longitude (Ls) ~ 185º with derived dust optical depths exceeding 6. The dust loading remained enhanced until Ls ~ 270º, before settling back towards opacities between 1 and 2. A second storm, the C storm, was observed at Ls ~ 330º where dust opacities again exceeded 2. Shortly after the C storm the dust settled back to seasonal values between 0.5 and 1.

[1] Patel, M. R. et al., Applied (2017)
[2] Neefs, E, et al. Applied optics (2015)
[3] Stamnes, K, et al. Applied optics (1988).
[4] Wolff, M. J. et al Icarus (2010)
[5] Wolff, M. J. et al. Icarus (2019).
[6] Clancy, R. T, et al. Icarus (2016).