Photoelectrons on closed crustal field lines at Mars

Trantham, Matthew; Liemohn, Michael W.; Mitchell, David; Frank, J.

doi:10.1029/2010ja016231

Cited by 14 publications

(35 citation statements)

References 37 publications

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“…The influence of the other parameters—EUV, SZAm and LT—is less clear and depends on the frame considered (for the LT influence in MSO versus MSE) or on cross‐correlations biases with the major drivers (for SZA near noon, as detailed above), even if the risks of artificial correlations as determined from Fisher's tests are always below 1%, except for the SZA influence (risk of ≈2%). Regarding the EUV influence, we point out that if EUV is a major driver for the photoelectron fluxes (Trantham et al, ; Xu et al, ) through the production mechanisms, its influence on the PEB should be less strong (e.g., the MGS data could not see any EUV influence on the ionopause, Mitchell et al, ). The EUV influence corresponds to an enhanced thermal pressure that will act against the solar wind confinement and thus push the draping of the IMF.…”

Section: The Parameters Of Influence For the Peb: Solar Wind Dynamic mentioning

confidence: 94%

The Martian Photoelectron Boundary as Seen by MAVEN

et al. 2017

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Photoelectron peaks in the 20–30 eV energy range are commonly observed in the planetary atmospheres, produced by the intense photoionization from solar 30.4 nm photons. At Mars, these photoelectrons are known to escape the planet down its tail, making them tracers for the atmospheric escape. Furthermore, their presence or absence allow to define the so‐called photoelectron boundary (PEB), which separates the photoelectron dominated ionosphere from the external environment. We provide here a detailed statistical analysis of the location and properties of the PEB based on the Mars Atmosphere and Volatile EvolutioN (MAVEN) electron and magnetic field data obtained from September 2014 to May 2016 (including 1696 PEB crossings). The PEB appears as mostly sensitive to the solar wind dynamic and crustal fields pressures. Its variable altitude thus leads to a variable wake cross section for escape (up to ∼+50%), which is important for deriving escape rates. The PEB is not always sharp and is characterized on average by the following: a magnetic field topology typical for the end of magnetic pileup region above it, more field‐aligned fluxes above than below, and a clear change of the altitude slopes of both electron fluxes and total density (that appears different from the ionopause). The PEB thus appears as a transition region between two plasma and fields configurations determined by the draping topology of the interplanetary magnetic field around Mars and much influenced by the crustal field sources below, whose dynamics also impacts the estimated escape rate of ionospheric plasma.

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Section: The Parameters Of Influence For the Peb: Solar Wind Dynamic mentioning

confidence: 94%

The Martian Photoelectron Boundary as Seen by MAVEN

et al. 2017

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“…The exclusion of these fluxes should barely affect the findings of this study. Figure e is the local EUV proxy, i.e., F 10.7 cm solar flux at Mars multiplying a solar zenith angle‐dependent Chapman function [ Trantham et al , ], against time. The very low values during southern summer [ Liemohn et al , , Figure 1c], when the crustal fields were at LT 2 A.M. but partially illuminated due to the tilt of the planet, are also excluded as the partially illuminated magnetic loops very likely straddle the terminator, and therefore, these fluxes may behave differently.…”

Section: Methodsmentioning

confidence: 99%

Mars photoelectron energy and pitch angle dependence on intense lower atmospheric dust storms

Liemohn

Mitchell

et al. 2014

J. Geophys. Res. Planets

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We have conducted a survey of the Mars Global Surveyor (MGS) electron data across all the pitch angles of 12 usable energy bins (11-746 eV) for dayside photoelectron observations over regions of strong crustal fields. Studies have shown that solar EUV flux is the main controlling factor, but dust storms play an important role as well. Our study of different energies and pitch angles has shown that the unusual bimodal solar flux dependence is not a common feature but mainly found in low energies and a few bins of higher-energy channels. By multiplying time-history dust opacity with a solar EUV proxy as a new controlling function, the statistically significant increase of the correlation of photoelectron flux against this function indicates that dust storms have a long-lasting influence on high-altitude photoelectron fluxes, especially at low energies and the pitch angle source regions of high-energy channels. The correlation increases experienced by the pitch angle source regions of all examined energy channels suggest that dust storms' influence most likely happens in the thermosphere-ionosphere source region of the photoelectrons, rather than at exospheric altitudes at or above MGS. Furthermore, by isolating the global-scale dust storm in Mars year 25 (2001) from the rest, the results suggest that this storm is entirely responsible for the second solar flux-dependent trend. While not excluding the possibility of this phenomenon being a one-time event, we hypothesize that there is a threshold of dust opacity at which the low-altitude dust's influence on high-altitude photoelectron fluxes begins to be significant.

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“…Radial B field of Mars [ Connerney et al , ], with the white box representing the geographic selection boundaries of this study, also Figure 1 of Trantham et al []. Copyright (2005) National Academy of Sciences, USA.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, any open magnetic field within the cusp region is more likely to be seen at large magnetic elevation angle at the MGS altitude. Another constraint, an absolute magnitude elevation angle observed by MGS MAG greater than 45°, is applied, because the chance to observe solar wind/magnetosheath electrons at smaller angles is very low [ Liemohn et al , ; Trantham et al , ]. A minimum magnetic field strength of 35 nT to ensure strong crustal fields and a maximum SZA of 90° to select dayside data are also applied.…”

Section: Methodsmentioning

confidence: 99%

Solar wind electron precipitation into the dayside Martian upper atmosphere through the cusps of strong crustal fields

Liemohn

Mitchell

2014

JGR Space Physics

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Measurements made by the magnetometer/electron reflectometer on board the Mars Global Surveyor spacecraft have shown spatially localized enhancements in electron fluxes over the strong crustal fields on both the dayside and night, which are used to identify the cusps in between the closed magnetic fields. This paper provides a comprehensive statistical study on the occurrence rate of dayside solar wind/magnetosheath precipitation over the strong crustal fields. Also, the occurrence rate's dependence on the magnetic elevation angles and the solar zenith angle is presented. A seasonal variation of the precipitation is also expected and found, due to both the tilt and the orbital eccentricity of Mars. The maximum occurrence rate is 40%, when the solar zenith angles are small and the magnetic fields are nearly vertical. Finally, the energy flux deposition of the solar wind electrons is calculated as well, which is 0.1%–2% of solar EUV flux input.

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Photoelectrons on closed crustal field lines at Mars

Cited by 14 publications

References 37 publications

The Martian Photoelectron Boundary as Seen by MAVEN

The Martian Photoelectron Boundary as Seen by MAVEN

Mars photoelectron energy and pitch angle dependence on intense lower atmospheric dust storms

Solar wind electron precipitation into the dayside Martian upper atmosphere through the cusps of strong crustal fields

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