Global Vertical Distribution of Water Vapor on Mars: Results From 3.5 Years of ExoMars‐TGO/NOMAD Science Operations

Abstract

We present water vapor vertical distributions on Mars retrieved from 3.5 years of solar occultation measurements by Nadir and Occultation for Mars Discovery onboard the ExoMars Trace Gas Orbiter, which reveal a strong contrast between aphelion and perihelion water climates. In equinox periods, most of water vapor is confined into the low‐middle latitudes. In aphelion periods, water vapor sublimated from the northern polar cap is confined into very low altitudes—water vapor mixing ratios observed at the 0–5 km lower boundary of measurement decrease by an order of magnitude at the approximate altitudes of 15 and 30 km for the latitudes higher than 50°N and 30–50°N, respectively. The vertical confinement of water vapor at northern middle latitudes around aphelion is more pronounced in the morning terminators than evening, perhaps controlled by the diurnal cycle of cloud formation. Water vapor is also observed over the low latitude regions in the aphelion southern hemisphere (0–30°S) mostly below 10–20 km, which suggests north‐south transport of water still occurs. In perihelion periods, water vapor sublimated from the southern polar cap directly reaches high altitudes (>80 km) over high southern latitudes, suggesting more effective transport by the meridional circulation without condensation. We show that heating during perihelion, sporadic global dust storms, and regional dust storms occurring annually around 330° of solar longitude (LS) are the main events to supply water vapor to the upper atmosphere above 70 km.

Carbon Dioxide Retrievals From NOMAD‐SO on ESA's ExoMars Trace Gas Orbiter and Temperature Profile Retrievals With the Hydrostatic Equilibrium Equation: 2. Temperature Variabilities in the Mesosphere at Mars Terminator

“…(2020) highlighted the importance of atmospheric temperature to control the water vapor abundances in the middle atmosphere and its vertical transport, which were confirmed as well by Aoki, Vandaele, et al. (2022) and Brines et al. (2022).…”

“…Starichenko et al (2021) analyzed the gravity wave activity in 144 temperature profiles from the Mid-InfraRed (MIR) channel of the Atmospheric Chemistry Suite (ACS) recorded during the second half of MY 34. Aoki et al (2019), Belyaev et al (2021), Fedorova et al (2020), and Neary et al (2020) highlighted the importance of atmospheric temperature to control the water vapor abundances in the middle atmosphere and its vertical transport, which were confirmed as well by Aoki, Vandaele, et al (2022) and Brines et al (2022).…”

Water Vapor Vertical Distribution on Mars During Perihelion Season of MY 34 and MY 35 With ExoMars‐TGO/NOMAD Observations

“…Vertical profiles of H 2 O abundance from the NOMAD SO channel have been previously presented in a couple of papers (Aoki et al., 2019; Villanueva et al., 2021) and also in a companion paper in this issue (Aoki et al., 2022). In Aoki et al.…”

“…For that reason we have decided to analyze observations taken at the NOMAD SO diffraction order 134 (3,011–3,035 cm −1 ) and order 168 (3,775–3,805 cm −1 ). Order 134 has absorption H 2 O lines with a moderate intensity ( I ∼ 10 −21 cm −1 /(molecule ⋅ cm −2 )) allowing the study of the lower atmosphere where lines are not heavily spectrally saturated (Aoki et al., 2022), while order 168 has stronger lines ( I ∼ 10 −19 cm −1 /(molecule ⋅ cm −2 )) allowing the sounding at higher altitudes. By spectral saturation, we refer to how the absorption lines penetrate into the continuum of the spectrum.…”

A Two‐Martian Years Survey of the Water Vapor Saturation State on Mars Based on ACS NIR/TGO Occultations

“…The validation of NIR temperature profiles against ACS MIR results obtained from the 2.7 μm band showed a good agreement for a wide set of simultaneous measurements (Alday et al., 2019, 2021; Belyaev et al., 2021; Fedorova et al., 2020). The water profiles were validated with the ACS MIR measurements in the 2.6 μm water band (Alday et al., 2021; Belyaev et al., 2021) and with simultaneous measurements of water vapor near 3.3 μm with NOMAD SO (Aoki et al., 2022).…”