Abstract
The vertical opacity structure of the martian atmosphere is important
for understanding the distribution of ice (water and carbon dioxide) and
dust. We present a new dataset of extinction opacity profiles from the
NOMAD/UVIS spectrometer aboard the ExoMars Trace Gas Orbiter, covering
one and a half Mars Years (MY) including the MY 34 Global Dust Storm and
several regional dust storms. We discuss specific mesospheric cloud
features and compare with existing literature and a Mars Global Climate
Model (MGCM) run with data assimilation. Mesospheric opacity features,
interpreted to be water ice, were present during the global and regional
dust events and correlate with an elevated hygropause in the MGCM,
providing further evidence for the role of regional dust storms in
driving atmospheric escape as reported elsewhere. The season of the dust
storms also had an apparent impact on the resulting lifetime of the
cloud features, with events earlier in the dusty season correlating with
longer-lasting mesospheric cloud layers. Mesospheric opacity features
were also present during the dusty season even in the absence of
regional dust storms, and interpreted to be water ice based on previous
literature. The assimilated MGCM temperature structure agreed well with
the UVIS opacities, but the MGCM opacity field struggled to reproduce
mesospheric ice features, suggesting a need for further development of
water ice parameterizations. The UVIS opacity dataset offers
opportunities for further research into the vertical aerosol structure
of the martian atmosphere, and for validation of how this is represented
in numerical models.