Geophysical Research Letters (2022)

The Nadir and Occultation for MArs Discovery (NOMAD)/UV-visible (UVIS) spectrometer on the ExoMars Trace Gas Orbiter provided observations of ozone (O3) and water vapor in the global dust storm of 2018. Here we show in detail, using advanced data filtering and chemical modeling, how Martian O3 in the middle atmosphere was destroyed during the dust storm. In data taken exactly 1 year later when no dust storm occurred, the normal situation had been reestablished. The model simulates how water vapor is transported to high altitudes and latitudes in the storm, where it photolyzes to form odd hydrogen species that catalyze O3. O3 destruction is simulated at all latitudes and up to 100 km, except near the surface where it increases. The simulations also predict a strong increase in the photochemical production of atomic hydrogen in the middle atmosphere, consistent with the enhanced hydrogen escape observed in the upper atmosphere during global dust storms.

JGR Planets (2022)

F. Daerden, L. Neary, G. Villanueva, G. Liuzzi, S. Aoki, R. T. Clancy, J. A. Whiteway, B. J. Sandor, M. D. Smith, M. J. Wolff, A. Pankine, A. Khayat, R. Novak, B. Cantor, M. Crismani, M. J. Mumma, S. Viscardy, J. Erwin, C. Depiesse, A. Mahieux, A. Piccialli, S. Robert, L. Trompet, Y. Willame, E. Neefs, I. R. Thomas, B. Ristic, A. C. Vandaele

The vertical profiles of water vapor and its semi-heavy hydrogen isotope HDO provided by instruments on ExoMars Trace Gas Orbiter constitute a unique new data set to understand the Martian water cycle including its isotopic composition. As water vapor undergoes hydrogen isotopic fractionation upon deposition (but not sublimation), the D/H isotopic ratio in water is a tracer of phase transitions, and a key quantity to understand the long-term history of water on Mars. Here, we present 3D global simulations of D/H in water vapor and compare them to the vertically resolved observations of D/H and water ice clouds taken by NOMAD during the second half of Mars year 34. D/H is predicted to be constant with height up to the main cloud level, above which it drops because of strong fractionation, explaining the upper cut-off in the NOMAD observations when HDO drops below detectability. During the global and regional dust storms of 2018/2019, we find that HDO ascends with H2O, and that the D/H ratio is constant and detectable up to larger heights. The simulations are within the provided observational uncertainties over wide ranges in season, latitude and height. Our work provides evidence that the variability of the D/H ratio in the lower and middle atmosphere of Mars is controlled by fractionation on water ice clouds, and thus modulated by diurnally and seasonally varying cloud formation. We find no evidence of other processes or reservoirs that would have a significant impact on the D/H ratio in water vapor.

Space Science Reviews (2021)

C.E. Newman, M. de la Torre, J. Pla-Garcia, T. Bertrand, M. A. Kahre, R. J. Wilson, F. Daerden, L. Neary, S. R. Lewis, F. Forget, A. Spiga, R. Sullivan, M.I. Richardson, A. Sanchez-Lavega, D. Viudez-Moreiras, B. Chide, and J.A. Rodriguez-Manfredi

Nine simulations are used to predict the meteorology and aeolian activity of the Mars 2020 landing site region. Predicted seasonal variations of pressure and surface and atmospheric temperature generally agree. Minimum and maximum pressure is predicted at Ls∼145◦and 250◦, respectively. Maximum and minimum surface and atmospheric temperature are predicted at Ls∼180◦and 270◦, respectively; i.e., are warmest at northern fall equinox not summer solstice. Daily pressure cycles vary more between simulations, possibly due to differences in atmospheric dust distributions. Jezero crater sits inside and close to the NW rim of the huge Isidis basin, whose daytime upslope (∼east-southeasterly) and night-time downslope (∼northwesterly) winds are predicted to dominate except around summer solstice, when the global circulation produces more southerly wind directions. Wind predictions vary hugely, with annual maximum speeds varying from 11 to 19 ms−1 and daily meanwind speeds peaking in the first half of summer for most simulations but in the second half of the year for two. Most simulations predict net annual sand transport toward the WNW, which is generally consistent with aeolian observations, and peak sand fluxes in the first half of summer, with the weakest fluxes around winter solstice due to opposition between the global circulation and daytime upslope winds. However, one simulation predicts transport toward the NW, while another predicts fluxes peaking later and transport toward the WSW. Vortex activity is predicted to peak in summer and dip around winter solstice, and to be greater than at InSight and much greater than in Gale crater.

Icarus (2021)

Michael D. Smith, Frank Daerden, Lori Neary, Alain S.J. Khayat, James A. Holmes, Manish R. Patel, Geronimo Villanueva, Giuliano Liuzzi, Ian R. Thomas, Bojan Ristic, Giancarlo Bellucci, Jose Juan Lopez-Moreno, Ann Carine Vandaele

More than a full Martian year of observations have now been made by the Nadir Occultation for MArs Discovery (NOMAD) instrument suite on-board the ExoMars Trace Gas Orbiter. Radiative transfer modeling of NOMAD observations taken in the nadir geometry enable the seasonal and global-scale variations of carbon monoxide gas in the Martian atmosphere to be characterized. These retrievals show the column-averaged volume mixing ratio of carbon monoxide to be about 800 ppmv, with significant variations at high latitudes caused by the condensation and sublimation of the background CO2 gas. Near summer solstice in each hemisphere, the CO volume mixing ratio falls to 400 ppmv in the south and 600 ppmv in the north. At low latitudes, carbon monoxide volume mixing ratio inversely follows the annual cycle of surface pressure. Comparison of our retrieved CO volume mixing ratio against that computed by the GEM-Mars general circulation model reveals a good match in their respective seasonal and spatial trends, and can provide insight into the physical processes that control the distribution of CO gas in the current Martian atmosphere.

Journal of Geophysical Research: Planets (2021) https://

Alain S. J. Khayat, Michael D. Smith, Michael Wolff, Frank Daerden, Lori Neary, Manish R. Patel, Arianna Piccialli, Ann C. Vandaele, Ian Thomas, Bojan Ristic, Jon Mason, Yannick Willame, Cedric Depiesse, Giancarlo Bellucci, and José Juan López-Moreno

Solar occultations performed by the Nadir and Occultation for MArs Discovery (NOMAD) ultraviolet and visible spectrometer (UVIS) onboard the ExoMars Trace Gas Orbiter (TGO) have provided a comprehensive mapping of atmospheric ozone density. The observations here extend over a full Mars year (MY) between April 21, 2018 at the beginning of the TGO science operations during late northern summer on Mars (MY 34, Ls = 163°) and March 9, 2020 (MY 35). UVIS provided transmittance spectra of the Martian atmosphere allowing measurements of the vertical distribution of ozone density using its Hartley absorption band (200–300 nm). The overall comparison to water vapor is found in the companion paper to this work (Patel et al., 2021, ). Our findings indicate the presence of (a) a high-altitude peak of ozone between 40 and 60 km in altitude over the north polar latitudes for at least 45% of the Martian year during midnorthern spring, late northern summer-early southern spring, and late southern summer, and (b) a second, but more prominent, high-altitude ozone peak in the south polar latitudes, lasting for at least 60% of the year including the southern autumn and winter seasons. When present, both high-altitude peaks are observed in the sunrise and sunset occultations, suggesting that the layers could persist during the day. Results from the Mars general circulation models predict the general behavior of these peaks of ozone and are used in an attempt to further our understanding of the chemical processes controlling high-altitude ozone on Mars.