Ionization Efficiency in the Dayside Martian Upper Atmosphere

Cui, Jun; Wu, Xiaoshu; Xu, Shaosui; Wang, X.-D.; Wellbrock, A.; Nordheim, Tom; Cao, Y.; Wang, W.-R.; Sun, Wenyi; Wu, Su Jun; Wei, Yong

doi:10.3847/2041-8213/aabcc6

Cited by 26 publications

(26 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The available EUVM data reveal near identical median solar EUV/X‐ray spectra for the four different cases of geophysical condition (not shown), implying that the case‐to‐case variability in the photoionization rate is primarily contributed by the variability in the background neutral atmosphere. Analogous to Cui, Wu, et al (), we calculate the photoionization rate along each MAVEN orbit using both the NGIMS neutral density data (Mahaffy et al, ) and the EUVM solar spectral model (Thiemann et al, ). The spherical nature of the atmosphere is taken into full account (Smith & Smith, ).…”

Section: Implications On Plasma Sourcesmentioning

confidence: 99%

Structural Variability of the Nightside Martian Ionosphere Near the Terminator: Implications on Plasma Sources

Cao

Cui

et al. 2019

JGR Planets

Self Cite

View full text Add to dashboard Cite

With the aid of the Neutral Gas and Ion Mass Spectrometer measurements made onboard the Mars Atmosphere and Volatile Evolution, we examine the morphology of the nightside Martian ionosphere near the terminator at 150–250 km in terms of the extension into darkness for a selected set of ion species: O 2+, NO+, HNO+, N 2+/CO+, CO 2+, and HCO+. Our analysis reveals several interesting characteristics, including the presence of dawn‐dusk and north‐south asymmetries and the variability among different species. A full interpretation of the Neutral Gas and Ion Mass Spectrometer observations relies on the combination of impact ionization by precipitating electrons and day‐to‐night plasma transport, as two important sources of plasma in the nightside Martian ionosphere near the terminator. The former partially contributes to the north‐south asymmetry, whereas the latter favorably explains not only the dawn‐dusk asymmetry but also NO+ and HCO+ as two exceptions which are more extended into darkness as compared to the other species on the dusk side. A comparison between the two plasma sources further indicates that the effect of day‐to‐night transport tends to be suppressed over the southern hemisphere. The above results highlight the impacts of crustal magnetic fields on the structural variability of the nightside Martian ionosphere near the terminator, manifest as the shielding of precipitating electrons and the suppression of day‐to‐night transport, both by the presence of strong magnetic anomalies clustering over the southern hemisphere of the planet.

show abstract

Section: Implications On Plasma Sourcesmentioning

confidence: 99%

Structural Variability of the Nightside Martian Ionosphere Near the Terminator: Implications on Plasma Sources

Cao

Cui

et al. 2019

JGR Planets

Self Cite

View full text Add to dashboard Cite

show abstract

“…For a closer look, we compare in Figure the energy distributions of these rates at two representative altitudes: 160 km near the periapsis (panel a) and 200 km (panel b). Both panels suggest that the contribution of secondary ionization is of minor importance, consistent with the relatively small ionization efficiency reported by Cui J et al () also based on the MAVEN data. For the two photoelectron loss processes, the relative importance of Coulomb collisions clearly increases with decreasing photoelectron energy.…”

Section: Photoelectron Balance During Maven Orbit No 2909mentioning

confidence: 99%

Photoelectron balance in the dayside Martian upper atmosphere

Cui

et al. 2019

Earth and Planetary Physics

View full text Add to dashboard Cite

Photoelectrons are produced by solar Extreme Ultraviolet radiation and contribute significantly to the local ionization and heat balances in planetary upper atmospheres. When the effect of transport is negligible, the photoelectron energy distribution is controlled by a balance between local production and loss, a condition usually referred to as local energy degradation. In this study, we examine such a condition for photoelectrons near Mars, with the aid of a multi‐instrument Mars Atmosphere and Volatile Evolution data set gathered over the inbound portions of a representative dayside MAVEN orbit. Various photoelectron production and loss processes considered here include primary and secondary ionization, inelastic collisions with atmospheric neutrals associated with both excitation and ionization, as well as Coulomb collisions with ionospheric thermal electrons. Our calculations indicate that photoelectron production occurs mainly via primary ionization and degradation from higher energy states during inelastic collisions; photoelectron loss appears to occur almost exclusively via degradation towards lower energy states via inelastic collisions above 10 eV, but the effect of Coulomb collisions becomes important at lower energies. Over the energy range of 30–55 eV (chosen to reduce the influence of the uncertainty in spacecraft charging), we find that the condition of local energy degradation is very well satisfied for dayside photoelectrons from 160 to 250 km. No evidence of photoelectron transport is present over this energy range.

show abstract

“…First, as electrons and low‐energy ions are magnetized above the collisional atmosphere, magnetic topology is important for characterizing energetic electron precipitation and low‐energy ion escape. More specifically, solar wind electrons and solar energetic particle electrons can precipitate along open field lines (e.g., Dubinin, Fraenz, Woch, Winnigham, et al, ; Dubinin, Fraenz, Woch, Roussos, et al, ; Lillis & Brain, ; Lillis et al, , , ; Xu et al, ), and ionospheric photoelectrons can precipitate onto the nightside atmosphere along cross‐terminator closed field lines (e.g., Liemohn et al, ; Ulusen et al, ; Xu, Mitchell, et al, ; Xu, Mitchell, Liemohn, et al, ), causing heating (e.g., Fox & Dalgarno, ; Sakai et al, ), ionization (e.g., Adams et al, ; Cui et al, ; Fillingim et al, , ; Xu, Mitchell, et al, ), and auroral emission (e.g., Bertaux et al, ; Brain et al, ; Haider et al, ; Leblanc et al, , ; Schneider et al, , ; Seth et al, ; Shane et al, ). At the same time, low‐energy ions can escape along open field lines (e.g., Ergun et al, ; Jakosky et al, ), accelerated partly by ambipolar electric fields (e.g., Collinson et al, ; Xu, Mitchell, et al, ), and on draped field lines through the J × B force and/or the convection electric field (e.g., Cravens et al, ; Fang et al, ; Halekas, Brain, et al, ).…”

Section: Introductionmentioning

confidence: 99%

A Technique to Infer Magnetic Topology at Mars and Its Application to the Terminator Region

et al. 2019

View full text Add to dashboard Cite

Magnetic topology is important for understanding the Martian plasma environment, including particle precipitation, energy transport, cold ion escape, and wave-particle interaction. In this study, we combine two independent but complementary methods in order to determine magnetic topology based on superthermal electron energy and pitch angle distributions. This approach removes ambiguities that result from using either energy or pitch angle alone, providing a more accurate and comprehensive determination of magnetic topology than previous studies. By applying this combined technique, we are able to identify seven magnetic topologies, including four types of closed field lines, two types of open field lines, and draped. All seven topologies are present in the Mars environment and are mapped in longitude, latitude, solar zenith angle, and altitude with the combined technique near the terminator. We find that closed field lines with double-sided loss cones are frequently present over stronger crustal field regions at higher altitudes. We also show that the cross-terminator closed field lines are more spatially confined over strong crustal regions, likely connecting nearby magnetic crustal patches. In contrast, cross-terminator closed loops over weak crustal regions have more distantly separated foot points, most likely connecting distant crustal patches. Key Points:• A technique combining e-pitch angle and energy distribution is developed to most accurately infer up to seven magnetic topologies at Mars • Closed magnetic loops with trapped electrons occur frequently over stronger crustal field regions at higher altitudes • Cross-terminator closed loops are more spatially confined over strong crustal regions and distantly separated over weak crustal regions Supporting Information:• Supporting Information S1

show abstract

Ionization Efficiency in the Dayside Martian Upper Atmosphere

Cited by 26 publications

References 43 publications

Structural Variability of the Nightside Martian Ionosphere Near the Terminator: Implications on Plasma Sources

Structural Variability of the Nightside Martian Ionosphere Near the Terminator: Implications on Plasma Sources

Photoelectron balance in the dayside Martian upper atmosphere

A Technique to Infer Magnetic Topology at Mars and Its Application to the Terminator Region

Contact Info

Product

Resources

About