ExoMars TGO/NOMAD‐UVIS Vertical Profiles of Ozone: 1. Seasonal Variation and Comparison to Water. Issue 11 (18th November 2021)

• Record Type: Journal Article
• Authors: Patel, M. R.; Sellers, G.; Mason, J. P.; Holmes, J. A.; Brown, M. A. J.; Lewis, S. R.; Rajendran, K.; Streeter, P. M.; Marriner, C.; Hathi, B. G.; Slade, D. J.; Leese, M. R.; Wolff, M. J.; Khayat, A. S. J.; Smith, M. D.; Aoki, S.; Piccialli, A.; Vandaele, A. C.; Robert, S.; Daerden, F.; Thomas, I. R.; Ristic, B.; Willame, Y.; Depiesse, C.; Bellucci, G.; Lopez‐Moreno, J.‐J.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 11(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-18
• Subjects: Solar occultation -- ultraviolet observations -- Mars -- spectroscopy -- ozone -- ExoMars; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2021JE006837
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: We present ∼1.5 Mars Years (MY) of ozone vertical profiles, covering L S = 163° in MY34 to L S = 320° in MY35, a period which includes the 2018 global dust storm. Since April 2018, the Ultraviolet and Visible Spectrometer channel of the Nadir and Occultation for Mars Discovery (NOMAD) instrument aboard the ExoMars Trace Gas Orbiter has observed the vertical, latitudinal and seasonal distributions of ozone. Around perihelion, the relative abundance of both ozone and water (from coincident NOMAD measurements) increases with decreasing altitude below ∼40 km. Around aphelion, localized decreases in ozone abundance exist between 25 and 35 km coincident with the location of modeled peak water abundances. High‐latitude (>±55°), high altitude (40–55 km) equinoctial ozone enhancements are observed in both hemispheres ( L S ∼350°–40°) and discussed in the companion article to this work (Khayat et al., 2021). The descending branch of the main Hadley cell shapes the observed ozone distribution at L S = 40°–60°, with the possible signature of a northern hemisphere thermally indirect cell identifiable from L S = 40°–80°. Morning terminator observations show elevated ozone abundances with respect to evening observations, with average ozone abundances between 20 and 40 km an order of magnitude higher at sunrise compared to sunset, attributed to diurnal photochemical partitioning along the line of sight between ozone and O or fluctuations in water abundance. The ozone retrievals presented here provide the most complete global description of Mars ozone vertical distributions to date as a function of season and latitude. Plain Language Summary: We present over two years of new observations of the vertical distribution of ozone in the atmosphere of Mars. The ExoMars Trace Gas Orbiter spacecraft has been recording observations of the Martian atmosphere since 2018 to map the presence and changes in abundance of gases such as ozone by using the "Nadir and Occultation for Mars Discovery (NOMAD)" instrument. NOMAD continually observes the change in ozone abundance (among other gases) at different heights across much of the planet. These abundance profiles have revealed the presence of distinct layers of ozone enhancement at high altitudes in the atmosphere of Mars toward the polar regions and between spring and autumn in the southern hemisphere of Mars, discussed in detail in the companion article. We observe broad periods where often the abundance of ozone follows the abundance of water from ∼10 km altitude up to ∼50 km altitude, and other times when the two appear to be opposite in their variation with height. Our retrievals of ozone from NOMAD data provide the first coincident observations of ozone and water and provide previously unavailable information on the photochemistry of Mars. Key Points: The annual Martian O3 distribution has been measured at a vertical resolution up to 0.2 km and for the first time alongside H2 O profiles O3 and H2 O show strong vertical anti‐correlation around aphelion as expected, contrasted with vertical correlation toward perihelion O3 abundances between altitudes of 20–40 km are an order of magnitude higher at sunrise than at sunset between L S = 40°–50°