MAVEN Observations of the Effects of Crustal Magnetic Fields on Electron Density and Temperature in the Martian Dayside Ionosphere

Flynn, Casey L.; Vogt, Marissa F.; Withers, Paul; Andersson, L.; England, S.; Liu, Guiping

doi:10.1002/2017gl075367

Cited by 46 publications

(64 citation statements)

References 29 publications

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“…The observation of enhanced neutral temperature was reported by Cui et al (2018) with the aid of the NGIMS data acquired during several DD campaigns (see also Leblanc et al 2006), but these authors argued that photoelectron trapping was unlikely to be a viable mechanism since the difference in photoelectron impact heating between regions with and without strong crustal magnetic fields was far insufficient to account for the difference in neutral temperature. Meanwhile, Flynn et al (2017) showed that regions over magnetic anomalies featured low electron temperatures, in contrast to our ideal expectation. According to Xu et al (2017), the magnetic field configuration throughout the entire atmospheric regions of interest here is dominated by closed field lines (see their Figure 8), indicating that photoelectrons are always trapped at these altitudes irrespective of the magnetic field strength.…”

Section: Discussion and Concluding Remarkscontrasting

confidence: 77%

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Cui

et al. 2018

ApJL

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Combining the Mars Atmosphere and Volatile Evolution measurements of neutral atmospheric density, solar EUV/X-ray flux, and differential photoelectron intensity made during 240 nominal orbits, we calculate the ionization efficiency, defined as the ratio of the secondary (photoelectron impact) ionization rate to the primary (photon impact) ionization rate, in the dayside Martian upper atmosphere under a range of solar illumination conditions. Both the CO 2 and O ionization efficiencies tend to be constant from 160km up to 250km, with respective median values of 0.19±0.03 and 0.27±0.04. These values are useful for fast calculation of the ionization rate in the dayside Martian upper atmosphere, without the need to construct photoelectron transport models. No substantial diurnal and solar cycle variations can be identified, except for a marginal trend of reduced ionization efficiency approaching the terminator. These observations are favorably interpreted by a simple scenario with ionization efficiencies, as a first approximation, determined by a comparison between relevant cross sections. Our analysis further reveals a connection between regions with strong crustal magnetic fields and regions with high ionization efficiencies, which are likely indicative of more efficient vertical transport of photoelectrons near magnetic anomalies.

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Section: Discussion and Concluding Remarkscontrasting

confidence: 77%

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Cui

et al. 2018

ApJL

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“…In the current paper, based on MAVEN data analysis, we show that the reason why the current models cannot accurately predict electron temperature in the high altitude of crustal‐field region is the neglect of kinetic effects, such as the magnetic mirror force and ambipolar electric field, on electron heat transport in the presence of crustal fields. The current paper also confirms the Flynn et al () conclusion just stated.…”

Section: Introductionsupporting

confidence: 91%

“…In both cases the magnetic field provides good connectivity between high and low altitudes in the ionosphere, that is, between ~100‐ and 500‐km altitudes, in comparison with the largely horizontal fields, namely, the draped magnetic field of solar wind origin (Bertucci et al, ; Brain et al, ). Flynn et al () showed that the electron density is higher (e.g., Andrews et al, , ) and temperature is lower in the dayside ionosphere of the crustal‐field regions above 200 km. They qualitatively anticipated that processes associated with plasma transport lead to the observed anticorrelation of electron densities and temperature in the crustal‐field region at Mars (e.g., Schunk & Nagy, ).…”

Section: Introductionmentioning

confidence: 99%

Low Electron Temperatures Observed at Mars by MAVEN on Dayside Crustal Magnetic Field Lines

et al. 2019

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The ionospheric electron temperature is important for determining the neutral/photochemical escape rate from the Martian atmosphere via the dissociative recombination of O2+. The Langmuir Probe and Waves instrument onboard MAVEN (Mars Atmosphere and Volatile EvolutioN) measures electron temperatures in the ionosphere. The current paper studies electron temperatures in the dayside for two regions where (1) crustal magnetic fields are dominant and (2) draped magnetic fields are dominant. Overall, the electron temperature is lower in the crustal‐field regions, namely, the strong magnetic field region, which is due to a transport of cold electrons along magnetic field lines from the lower to upper atmosphere. The electron temperature is also greater for high solar extreme ultraviolet conditions, which is associated with the local extreme ultraviolet energy deposition. The current models underestimate the electron temperature above 250‐km altitude in the crustal‐field region. Electron heat conduction associated with a photoelectron transport in the crustal‐field regions is altered due to kinetic effects, such the magnetic mirror and/or ambipolar electric field because the electron mean free path exceeds the relevant length scale for electron temperature. The mirror force can affect the electron and heat transport between low altitudes, where the neutral density and related electron cooling rates are the greatest, and high altitudes, while the ambipolar electric field decelerates the electron's upward motion. These effects have not been included in current models of the electron energetics, and consideration of such effects on the electron temperature in the crustal‐field region should be considered for future numerical simulations.

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“…For this purpose, the data from the MAVEN nominal science orbits may not be very useful since the impact of magnetic field is likely manifest at altitudes below their periapses. This is in contrast to the recent finding that a similar impact on electron temperature is manifest above 200km (Flynn et al 2017). …”

Section: Discussioncontrasting

confidence: 99%

The Impact of Crustal Magnetic Fields on the Thermal Structure of the Martian Upper Atmosphere

Cui

Yelle

Zhao

et al. 2018

ApJL

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Using the Mars Atmosphere and Volatile Evolution Neutral Gas and Ion Mass Spectrometer data, we investigate the possible impact of crustal magnetic fields on the thermal structure of the Martian upper atmosphere. Our analysis reveals a clear enhancement in temperature over regions with strong crustal magnetic fields during two deep dip campaigns covering the periods of April 17-22 and September 2-8, both in 2015. Several controlling factors, such as solar EUV irradiance, relative atomic O abundance, and non-migrating tides, do not help to explain the observed temperature enhancement, and a magnetically driven scenario is favored. We evaluate the roles of several heating mechanisms that are likely modulated by the presence of crustal magnetic fields, including Joule heating, ion chemical heating, as well as electron impact heating via either precipitating solar wind electrons or locally produced photoelectrons. The respective heating rates of these mechanisms are substantially lower than the solar EUV heating rate, implying that none of them is able to interpret the observations.

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MAVEN Observations of the Effects of Crustal Magnetic Fields on Electron Density and Temperature in the Martian Dayside Ionosphere

Cited by 46 publications

References 29 publications

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Low Electron Temperatures Observed at Mars by MAVEN on Dayside Crustal Magnetic Field Lines

The Impact of Crustal Magnetic Fields on the Thermal Structure of the Martian Upper Atmosphere

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