Variations in the Ionospheric Peak Altitude at Mars in Response to Dust Storms: 13 Years of Observations From the Mars Express Radar Sounder

Abstract

Previous observations have shown that, during Martian dust storms, the peak of the ionosphere rises in altitude. Observational studies of this type, however, have been extremely limited. Using 13 years of ionospheric peak altitude data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument on Mars Express, we study how the peak altitude responded to dust storms during six different Mars years (MY). The peak altitude increased ∼10-15 km during all six events, which include a local dust storm (MY 33), three regional dust storms (MYs 27, 29, and 32), and two global dust storms (MYs 28 and 34). The peak altitude's orbit-to-orbit variability was exceptionally large at the apexes of the MY 29 and MY 32 dust seasons and dramatically increased during the MY 28 and MY 34 global dust storms. We conclude that dust storms significantly increase upper atmospheric variability, which suggests that they enhance dynamical processes that couple the lower and upper atmospheres, such as upward propagating gravity waves or atmospheric tides. Plain Language SummaryLimited observations have shown that dust storms at Mars significantly affect the upper atmosphere and ionosphere. In particular, the expansion of the atmosphere in response to solar heating of dust causes fixed pressure levels in the upper atmosphere to rise in altitude. The peak of the ionosphere-where the maximum electron density occurs-can be used as a diagnostic of this expansion because it forms at a fixed pressure level in the upper atmosphere (120-150 km). In this work, we use 13 years of observations from the radar sounder on the Mars Express spacecraft to evaluate how the peak altitude of the ionosphere varied during six different dust storms. We found that the peak altitude increased by 10-15 km during each dust storm. Additionally, the orbit-to-orbit variability of the peak altitude increased significantly during the dust storms, which suggests that dynamical processes that couple the lower and upper atmospheres were enhanced.

Seasonal and Geographical Variability of the Martian Ionosphere From Mars Express Observations

“…We find that the peak densities, once corrected for the SZA, solar radiation output and seasonal variations, are larger over the crustal field regions, confirming previous results obtained with much smaller datasets (Nielsen et al, 2007) 6. The global dust storm in MY28 raised the altitude of the ionospheric peak by about 10-15 km, in agreement with a previous independent analysis of the MARSIS AIS data set (Girazian et al, 2020), with studies of the ionosphere during the MY34 dust storm (Felici et al, 2020), and with modeling results (Fang et al, 2020) Data Availability Statement MARSIS and MaRS data are available in the ESA PSA archive (ftp://psa.esac.esa.int/pub/mirror/MARS-EX-PRESS/MARSIS/ and ftp://psa.esac.esa.int/pub/mirror/MARS-EXPRESS/MRS/). All the data used in this study, including also derived magnitudes, have been made publicly available at Zenodo (https://doi.…”

“…While the data set used is the same in both studies, different methods are used to examine the effects of the storm. In particular, while we use the SZA-corrected peak altitudes, Girazian et al (2020) use the measured values without any further correction. The fact of obtaining similar results when using different methods gives confidence on the robustness of both analyses.…”

Martian Year 34 Column Dust Climatology from Mars Climate Sounder Observations: Reconstructed Maps and Model Simulations

“…Streeter et al, ); 2. a major component of the atmospheric interannual, seasonal, daily, and diurnal variability (see Kleinböhl et al, , for an example related to the diurnal variability); 3. a way to redistribute dust on the planet via long‐range particle transport (as inferred, for instance, using albedo changes: Szwast et al, ); 4. a means of producing perturbations of temperature and density, which propagate from the lower to the upper atmosphere, including the lower thermosphere, the ionosphere, and the magnetosphere (e.g. Girazian et al, ; Xiaohua et al, ); 5. a cause of increased loss of chemical species via escape (e.g. Fedorova et al, ; Heavens et al, ; Xiaohua et al, ); and 6. a source of hazards for spacecraft entry, descent, and landing maneuvers, for operations by solar‐powered surface assets, and for future robotic and human exploration (e.g.…”

Species‐dependent Response of the Martian Ionosphere to the 2018 Global Dust Event

“…Using 13 years’ observations made by the Mars Advanced Radar for Subsurface and Ionospheric Sounding onboard MEX, Girazian et al. (2020) also found that the peak altitude increased by 10 − 15 km during dust storms over six MYs. As demonstrated by the photochemical equilibrium model of Wang and Nielsen (2003), the elevation in peak ionospheric altitude is mainly attributed to the expansion of the neutral atmosphere during dust storms.…”