Global distribution and parameter dependences of gravity wave activity in the Martian upper thermosphere derived from MAVEN/NGIMS observations

Naoki Terada (1) , François Leblanc (2) , Hiromu Nakagawa (1) , Alexander S. Medvedev (3, 4) , Erdal Yiğit (5, 4) , Takeshi Kuroda (6, 1) , Takuya Hara (7) , Scott L. England (7) , Hitoshi Fujiwara (8) , Kaori Terada (1) , Kanako Seki (9, 10) , Paul R. Mahaffy (11) , Meredith Elrod (12, 11) , Mehdi Benna (11, 12) , Joseph Grebowsky (11) , Bruce M. Jakosky (13)

1 Graduate School of Information Sciences [Sendai]
2 HELIOS - LATMOS
3 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
4 Institut für Astrophysik [Göttingen]
5 Department of Physics and Astronomy [Fairfax]
6 NICT - National Institute of Information and Communications Technology [Tokyo]
7 SSL - Space Sciences Laboratory [Berkeley]
8 Faculty of Science and Technology [Tokyo]
9 Department of Earth and Planetary Science [Tokyo]
10 Graduate School of Science [Tokyo]
11 GSFC - NASA Goddard Space Flight Center
12 CRESST - Center for Research and Exploration in Space Science and Technology [GSFC]
13 LASP - Laboratory for Atmospheric and Space Physics [Boulder]

Wavelike perturbations in the Martian upper thermosphere observed by the Neutral Gas Ion Mass Spectrometer (NGIMS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have been analyzed. The amplitudes of small-scale perturbations with apparent wavelengths between ~100 and ~500 km in the Ar density around the exobase show a clear dependence on temperature (T0) of the upper thermosphere. The average amplitude of the perturbations is ~10% on the dayside and ~20% on the nightside, which is about 2 and 10 times larger than those observed in the Venusian upper thermosphere and in the low-latitude region of Earth's upper thermosphere, respectively. The amplitudes are inversely proportional to T0, suggesting saturation due to convective instability in the Martian upper thermosphere. After removing the dependence on T0, dependences of the average amplitude on the geographic latitude and longitude and solar wind parameters are found to be not larger than a few percent. These results suggest that the amplitudes of small-scale perturbations are mainly determined by convective breaking/saturation in the upper thermosphere on Mars, unlike those on Venus and Earth.

Mots clés: MAVEN; gravity waves; upper thermosphere; Mars

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]; Océan, Atmosphère

Naoki Terada, François Leblanc, Hiromu Nakagawa, Alexander S. Medvedev, Erdal Yiğit, et al.. Global distribution and parameter dependences of gravity wave activity in the Martian upper thermosphere derived from MAVEN/NGIMS observations. Journal of Geophysical Research Space Physics, 2017, 122 (2), pp.2374-2397. ⟨10.1002/2016JA023476⟩. ⟨insu-01492717⟩