Strong Variability of Martian Water Ice Clouds During Dust Storms Revealed From ExoMars Trace Gas Orbiter/NOMAD

Abstract

Observations of water ice clouds and aerosols on Mars can provide important insights into the complexity of the water cycle. Recent observations have indicated an important link between dust activity and the water cycle, as intense dust activity can significantly raise the hygropause, and subsequently increase the escape of water after dissociation in the upper atmosphere. Here present observations from Nadir and Occultation for MArs Discovery/Trace Gas Orbiter that investigate the variation of water ice clouds in the perihelion season of Mars year 34 (April 2018-2019), their diurnal and seasonal behavior, and the vertical structure and microphysical properties of water ice and dust. These observations reveal the recurrent presence of a layer of mesospheric water ice clouds subsequent to the 2018 global dust storm. We show that this layer rose from 45 to 80 km in altitude on a time scale of days from heating in the lower atmosphere due to the storm. In addition, we demonstrate that there is a strong dawn-dusk asymmetry in water ice abundance, related to nighttime nucleation and subsequent daytime sublimation. Water ice particle sizes are retrieved consistently and exhibit sharp vertical gradients (from 0.1 to 4.0 μm), as well as mesospheric differences between the global dust storm (<0.5 μm) and the 2019 regional dust storm (1.0 μm), which suggests differing water ice nucleation efficiencies. These results form the basis to advance our understanding of mesospheric water ice clouds on Mars, and further constrain the interactions between water ice and dust in the middle atmosphere.

Probing the Atmospheric Cl Isotopic Ratio on Mars: Implications for Planetary Evolution and Atmospheric Chemistry

“…As observed by Aoki et al (2021), the vertical distribution of HCl is very similar to water vapor, and in MY34 is observed between the GDS and the regional storm mostly at midlatitudes in the Southern Hemisphere Liuzzi et al, 2020). The HCl abundances observed during the same season in MY35 are comparable to MY34, suggesting that the simultaneous presence of dust and water vapor, rather than the abundance of dust itself, is key to HCl production.…”

“…As mentioned, the vertical distributions of HCl and H2O are very similar, therefore HCl is expected to be trapped in growing water ice particles (Kippenberger et al., 2019). While no water ice has been detected simultaneously with HCl observations, it has a diurnal cycle and the frequency of water ice clouds following the regional dust storm at L S 320 increases at midsouthern latitudes (Liuzzi et al., 2020), and could play a role in HCl depletion Similar to what happens on Earth with Polar Stratospheric Clouds, there may be heterogeneous chemistry on water ice by reaction with ClONO 2 , N 2 O 5 , HOCl (Solomon, 1999). In this case, HCl could be oxidized in Cl 2 or ClNO 2 .…”

Water heavily fractionated as it ascends on Mars as revealed by ExoMars/NOMAD

“…Strong isotopic anomalies are typically observed at regions with strong temperature/water gradients, like the polar caps, and these are typically hard to capture and sample at moderate spatial resolutions from the ground. In many cases, the observed variations of the D/H across seasons and with altitude revealed by our work could be attributed to Rayleigh fractionation and cloud formation (32), with the D/H decreasing with altitude and dropping or decreasing at the edge of the hygropause. In the zonal mean Fig.…”

Clouds in the Martian Atmosphere

“…Since TES, other instruments have contributed to the climatology of water ice clouds on Mars, such as ACS and NOMAD on the Trace Gas Orbiter (Fedorova et al, 2020;Liuzzi et al, 2020;Stcherbinine et al, 2020), THEMIS (Smith, 2019) on Mars Odyssey, MCS (McCleese et al, 2010), MARCI (Clancy et al, 2016;Wolff et al, 2019) on MRO, SPICAM (Montmessin et al, 2017;Willame et al, 2017), OMEGA (Madeleine et al, 2012;Olsen et al, 2019), andPFS (Giuranna et al, 2019) on the Mars Express mission, as well as in situ information delivered by the Phoenix (Whiteway et al, 2009) and the MSL (Kloos et al, 2016;McConnochie et al, 2018) missions.…”

“…As such, it is nearly independent of the particle shape and provides robust access to the particle properties. Since the Phobos mission, the characterization of cloud profiles has been documented from the UV to the thermal infrared (Benson et al, 2010(Benson et al, , 2011Fedorova et al, 2009Fedorova et al, , 2020Guzewich & Smith, 2019;Liuzzi et al, 2020;Määttänen et al, 2013;Maltagliati et al, 2013;McCleese et al, 2010;Rannou et al, 2006;Smith et al, 2013;Stcherbinine et al, 2020).…”