Dust-Storm-Driven Variability in the Martian Thermosphere and Ionosphere Observed by MAVEN/NGIMS

The Martian upper atmosphere exhibits strong variability driven by both external forcing from the Sun, like flares, interplanetary coronal Mass Ejection (iCME), and internal atmospheric processes ^[1]. Among the latter, regional and global dust storms modify the thermal structure and circulation of the lower atmosphere, with effects that can propagate upward into the thermosphere and exosphere ^[2]. It is important to understand how these processes alter the composition and structure of the upper atmosphere is essential for interpreting atmospheric escape and for future aeronomy investigations at Mars.

In this work, we investigate the response of the Martian thermosphere and ionosphere during the disturbed period of late March–early April 2015 using measurements from the Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard MAVEN. This interval coincided with both intense solar activity, including SEP/iCME events, and the development of a regional dust storm. To quantify the atmospheric response, quiet-time reference conditions were first established using MAVEN observations from 1–3 March 2015. Variations in neutral density profiles, scale heights, and composition were then examined for CO₂, O, N₂, and Ar in the 180–220 km altitude region.

The analysis reveals a clear thermospheric expansion in CO₂, N₂, and Ar densities during the disturbed period, while atomic oxygen exhibits a significant decrease above ~180 km. In addition, the O/CO₂ ratio decreases substantially, indicating a shift toward a more CO₂-dominated upper atmosphere. Density profiles also show signatures of wave-like structures, suggesting enhanced vertical coupling associated with dust-driven atmospheric dynamics. Dust maps constructed using Mars Climate Database simulations confirm the presence and growth of a regional dust storm during the same interval, supporting the interpretation that lower-atmosphere forcing played a major role in the observed thermospheric variability.

The ionospheric response derived from NGIMS ion measurements shows enhanced CO₂⁺ and O⁺ densities, whereas O₂⁺ remains comparatively stable. These variations appear closely linked to the changes in neutral composition and thermospheric structure. While simultaneous SEP/iCME activity may also have contributed to the observed perturbations, the results indicate that dust storm effects were likely the dominant driver of the large-scale neutral and ionospheric modifications during this period.

This study contributes to ongoing efforts to delineate the coupled influences of space weather and lower-atmospheric forcing on the Martian upper atmosphere and exosphere. The results are important in the context of the proposed M-MATISSE mission, particularly for the scientific definition of the M-INEA instrument, by helping identify the key neutral and ionized species, altitude regions, and variability signatures that future in situ investigations should target.

References

[1] Lee CO, Sánchez-Cano B, DiBraccio GA, Mayyasi M, Xu S, Chamberlin P, Davies E, Scolini C, Filwett RJ, Ramstad R, Palmerio E, Lynch BJ, Luhmann JG, Ehresmann B, Guo J, Allen RC, Vines S, Winslow R and Elliott H (2023), Heliophysics and space weather science at ∼1.5 AU: Knowledge gaps and need for space weather monitors at Mars.Front. Astron. Space Sci. 10:1064208. doi: 10.3389/fspas.2023.1064208

[2] Elrod, M. K., Bougher, S. W., Roeten, K., Sharrar, R., & Murphy, J. (2020). Structural and Compositional Changes in the Upper Atmosphere Related to the PEDE‐2018 Dust Event on Mars as Observed by MAVEN NGIMS. Geophysical Research Letters, 47, e2019GL084378. https://doi.org/10.1029/2019GL084378