First Ionospheric Results From the MAVEN Radio Occultation Science Experiment (ROSE)

Withers, Paul; Felici, M.; Mendillo, M.; Moore, Luke; Narvaez, C.; Vogt, Marissa F.; Jakosky, B. M.

doi:10.1029/2018ja025182

Cited by 41 publications

(46 citation statements)

References 35 publications

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“…During MY 33, the peak altitude increased by 10–15 km at L s 305° and at southern latitudes between −20° and −40°. Withers et al () reported MAVEN ROSE observations showing a similar increase in the peak altitude at the same time, but at northern latitudes near +50°. They attributed the elevated peak altitude to a small, localized dust storm near the south pole.…”

Section: Discussionmentioning

confidence: 71%

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

et al. 2020

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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.

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Section: Discussionmentioning

confidence: 71%

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

et al. 2020

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“…On 10 October 2017, the MAVEN Radio Occultation Science Experiment (ROSE; Withers et al, ) observed a transient layer near 60 km, whose peak electron concentration was 2.5 × 10 5 electrons/cm 3 (Figure ). Transient layers were not observed in any previous observations reported in the ROSE first results paper of Withers et al (). This layer is among the lowest altitude reported in the literature, with a concentration at the peak slightly above the average for this type of event.…”

Section: Previous Interpretation Of Transient Layersmentioning

confidence: 99%

Localized Ionization Hypothesis for Transient Ionospheric Layers

et al. 2019

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The persistent two-peaked vertical structure of the Martian ionosphere is created by extreme and far ultraviolet radiation whose energies, respectively, determine their ionization altitude. A third low-altitude transient layer (previously referred to as M3 or M m) has been observed by radio occultation techniques and attributed to meteor ablation. However, recent remote sensing and in situ observations disfavor a meteoric origin. Here we propose an alternative hypothesis for these apparent layers associated with impact ionization from penetrating solar wind ions, previously observed as proton aurora. Localized ionization, occurring nonglobally at a given altitude range, breaks the symmetry assumed by the radio occultation technique, and creates electron layers apparently lower in the ionosphere than their true altitude. This may occur when the upstream bow shock is altered by a radial interplanetary magnetic field configuration, which allows the solar wind to penetrate directly into the thermosphere. This localized ionization hypothesis provides an explanation for apparent layers' wide variation in heights and their transient behavior. Moreover, this hypothesis is testable with new observations by the Mars Atmospheric and Volatile EvolutioN Radio Occultation Science Experiment in future Mars years. This hypothesis has implications for the ionospheres of Venus and Titan, where similar transient layers have been observed. Plain Language Summary The ionosphere of a planet couples the neutral atmosphere to the exosphere and solar wind. Created by solar ionizing radiation, the ionosphere on the dayside of planet is expected to be hemispherically symmetric. When Mars Express discovered transient low-altitude ionospheric layers in 2005, they were initially predicted to be due to meteor ablation. However, recent observations indicate that they are due to a geometric observational effect related to local, not hemispheric, ionization. Observations from three instruments on Mars Atmospheric and Volatile EvolutioN are used concurrently to understand this phenomenon. These transient layers have been observed at Venus and Titan as well, and this hypothesis indicates novel physics for those ionospheric systems.

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“…First, radio occultation experiments can be used to derive electron density profiles, that is, electron densities as a function of the altitude, spanning the altitudes both below and above the peak altitude. These were performed using the Mariner 9 spacecraft (Kliore et al, , ; Withers, Weiner, et al, ), Mars Global Surveyor spacecraft (Hinson et al, ), Mars Express spacecraft (Grandin et al, ; Pätzold et al, ), and recently using the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft (Withers et al, ). The main disadvantage of these profiles is that their spatial coverage is restricted by geometric constraints imposed by the orbits of Earth and Mars (Tyler et al, ; Withers et al, ).…”

Section: Introductionmentioning

confidence: 99%

Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere

et al. 2019

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We use more than 10 years of the Martian topside ionospheric data measured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft to derive an empirical model of electron densities from the peak altitude up to 325 km. Altogether, 16,044 electron density profiles obtained at spacecraft altitudes lower than 425 km and at solar zenith angles lower than 80° are included in the analysis. Each of the measured electron density profiles is accurately characterized by the peak electron density, peak altitude, and three additional parameters describing the profile shape above the peak: (i) steepness at high altitudes, (ii) main layer thickness, and (iii) transition altitude. The dependence of these parameters on relevant controlling factors (solar zenith angle, solar irradiance, crustal magnetic field magnitude, and Sun‐Mars distance) is evaluated, allowing for a formulation of a simple empirical model. Mars Atmosphere and Volatile EvolutioN Extreme Ultraviolet monitor data are used to show that the solar ionizing flux can be accurately approximated by the F10.7 index when taking into account the solar rotation. Electron densities predicted by the resulting empirical model are compared with electron densities locally evaluated based on the Mars Advanced Radar for Subsurface and Ionosphere Sounding measurements, with the Langmuir Probe and Waves electron density measurements on board the Mars Atmosphere and Volatile EvolutioN spacecraft, and with electron densities obtained by radio occultation measurements. Although the electron densities measured by the Langmuir Probe and Waves instrument are systematically somewhat lower than the model electron densities, consistent with former findings, the model performs reasonably well.

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First Ionospheric Results From the MAVEN Radio Occultation Science Experiment (ROSE)

Cited by 41 publications

References 35 publications

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

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

Localized Ionization Hypothesis for Transient Ionospheric Layers

Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere

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