The vertical distribution of ozone in Mars Years 34-35 from ExoMars
TGO/NOMAD-UVIS observations
Abstract
We present ~1.5 Mars Years (MY) of ozone vertical
profiles, covering Ls = 163deg; in MY34 to Ls = 320deg; in MY35, a
period which includes the 2018 global dust storm. Since April 2018, the
Ultraviolet and Visible Spectrometer (UVIS) channel of the Nadir and
Occultation for Mars Discovery (NOMAD) spectrometer aboard the ExoMars
Trace Gas Orbiter has observed the vertical, latitudinal and seasonal
distributions of ozone. Around perihelion, the relative abundance of
ozone (and water from coincident NOMAD measurements) increases strongly
together below ~40 km. Around aphelion, decreases in
ozone abundance exist between 25-35 km coincident with the location of
modelled peak water abundances. We report high latitude (above 55deg;),
high altitude (40-55 km) equinoctial ozone enhancements in both
hemispheres. The northern equinoctial high altitude enhancement is
previously unobserved and forms prior to vernal equinox lasting for
almost 100 sols (Ls ~350‑40deg), whereas the southern
enhancement persists for over twice as long (Ls =
~5-140deg;). Both layers reform at autumnal equinox,
with the northern layer at a lower abundance. These layers likely form
through a combination of anti-correlation with water and the equinoctial
meridional transport of O and H atoms to high-latitude regions. The
descending branch of the main Hadley cell shapes the ozone distribution
at Ls = 40-60deg;, with the possible signature of a northern hemisphere
thermally indirect cell identifiable from Ls = 40-80deg;. The ozone
retrievals presented here provide the most complete global description
of Mars ozone vertical distributions as a function of season and
latitude.