Seasonal Transport in Mars’ Mesosphere-Thermosphere revealed by Nitric Oxide nightglow

Arnaud Stiepen (1) , Emilie M. Royer (2) , Nicholas Mccord Schneider (2) , Sonal Jain (2) , Zachariah Milby (2) , Justin Deighan (2) , Francisco Gonzalez-Galindo (3) , Stephen W. Bougher (4) , Jean-Claude Gérard (1) , Michael H. Stevens (5) , J. Scott Evans (6) , Ian F. Stewart (2) , Michael Chaffin (2) , Bill Mcclintock (2) , John T. Clarke (7) , Franck Montmessin (8) , Greg Holsclaw (2) , Franck Lefèvre (8) , François Forget (9) , Daniel Lo (10) , Benoit A. Hubert (1) , Bruce Martin Jakosky (2)

1 LPAP - Laboratoire de Physique Atmosphérique et Planétaire
2 LASP - Laboratory for Atmospheric and Space Physics [Boulder]
3 IAA - Instituto de Astrofísica de Andalucía
4 CLaSP - Department of Climate and Space Sciences and Engineering
5 NRL - Naval Research Laboratory
6 Computational Physics, Inc.
7 CSP - Center for Space Physics [Boston]
8 PLANETO - LATMOS
9 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
10 University of Arizona

We analyze the ultraviolet nightglow in the atmosphere of Mars through the Nitric Oxide (NO) δ and γ band emissions observed by the Imaging Ultraviolet Spectrograph (IUVS, McClintock et al., 2015) when the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft is at apoapsis and periapsis. On the dayside thermosphere of Mars, solar extreme ultraviolet radiation dissociates CO₂ and N₂ molecules. O(³P) and N(⁴S) atoms are carried by the day-to-night hemispheric transport. They descend in the nightside mesosphere, where they can radiatively recombine to form NO(C²Π). The excited molecules rapidly relax by emitting UV photons in the δ and γ bands. These emissions are thus indicators of the N and O atom fluxes transported from the dayside to Mars’ nightside and the descending circulation pattern from the nightside thermosphere to the mesosphere (e.g. Bertaux et al., 2005 ; Bougher et al., 1990 ; Cox et al., 2008 ; Gagné et al., 2013 ; Gérard et al., 2008 ; Stiepen et al., 2015, 2017). A large dataset of nightside disk images and vertical limb scans during southern winter, fall equinox and southern summer conditions have been accumulated since the beginning of the mission. We will present a discussion regarding the variability of the brightness and altitude of the emission with season, geographical position (longitude) and local time and possible interpretation for local and global changes in the mesosphere dynamics. We show the possible impact of atmospheric waves structuring the emission longitudinally and indicating a wave-3 structure in Mars’ nightside mesosphere. Quantitative comparison with calculations from the LMD-MGCM (Laboratoire de Météorologie Dynamique-Mars Global Climate Model) show that the model globally reproduces the trends of the NO nightglow emission and its seasonal variation but also indicates large discrepancies (up to a factor 50 fainter in the model) suggesting that the predicted transport is too efficient toward the night winter pole in the thermosphere by ∼20° latitude north. These questions are now addressed with an extensive dataset of disk images, complemented with improved simulations from the LMD-MGCM and new M-GITM (Mars Global Ionosphere-Thermosphere Model) simulations of emissions for selected sampling periods.

Domaines: Planète et Univers [physics]

Arnaud Stiepen, Emilie M. Royer, Nicholas Mccord Schneider, Sonal Jain, Zachariah Milby, et al.. Seasonal Transport in Mars’ Mesosphere-Thermosphere revealed by Nitric Oxide nightglow. AGU 2017 Fall MeetingU, Dec 2017, New Orleans, United States. ⟨insu-01683182⟩