The Influence of Solar Wind Pressure on Martian Crustal Magnetic Field Topology

Weber, Tristan; Brain, David; Mitchell, David; Xu, Shaosui; Espley, J. R.; Halekas, J. S.; Lillis, R. J.; Jakosky, B. M.

doi:10.1029/2019gl081913

Cited by 42 publications

(46 citation statements)

References 52 publications

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“…Thus, as solar wind pressure decreases, crustal field regions are more likely to have closed topology at the 400 km altitude of MGS. Similar trends have been noted by Weber et al (2019) based on MAVEN observations.…”

Section: Resultssupporting

confidence: 91%

Variations in Nightside Magnetic Field Topology at Mars

Brain

Weber

et al. 2020

Geophysical Research Letters

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The Martian plasma environment contains a complex magnetic topology, with contributions from the interplanetary magnetic field (IMF) and crustal magnetic fields. The topology can control how plasma is exchanged between the solar wind and the Martian ionosphere. Here we use 7 years of suprathermal electron pitch angle distributions recorded by the Mars Global Surveyor (MGS) spacecraft to determine the topology at 2 am and 400 km on the Martian nightside as a function of geographic location and external drivers. Observations show that topology statistically varies with IMF direction, solar wind pressure, solar extreme ultraviolet (EUV) flux, and season. Changes in topology with IMF direction and season are consistent with changes in the likelihood of magnetic reconnection between individual crustal fields and the draped IMF. Changes in topology at a given location with solar wind pressure and solar EUV flux are consistent with reconfiguration of topological structures in the plasma environment.

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Section: Resultssupporting

confidence: 91%

Variations in Nightside Magnetic Field Topology at Mars

Brain

Weber

et al. 2020

Geophysical Research Letters

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“…This issue is visited in the present study by focusing on a subset of the SWEA spectrum, that is, those presenting electron depletions, and using the occurrence rate of these depletions as a proxy of the magnetic connectivity on the nightside of Mars. Our analysis of the SWEA electron energy spectra, combined with the SWIA‐based estimates of the upstream SW condition, confirms the scenario proposed recently by Weber et al () that under high SW dynamic pressures, the compression of the Martian magnetosphere leads to a more open magnetic field topology, which allows easier SW access to the ionosphere (see Figures 7–10). Our results, while obtained from a large data set mostly under quiet SW conditions, are also consistent with the reported SW modulation of magnetic connectivity near Mars under extreme SW conditions such as during the passage of an ICME (e.g., Xu et al, , ).…”

Section: Discussionsupporting

confidence: 89%

“…The SW control of electron depletions is presented in Figure in terms of the distribution of depletions with respect to altitude and SW dynamic pressure, including all SWEA measurements made at SZA>120°. The figure reveals a systematic decrease in the probability of observing electron depletions with increasing SW dynamic pressure, which is an expected trend because under high SW dynamic pressures, the compression of the Martian magnetosphere leads to a more open magnetic field topology, which allows easier SW access to the ionosphere (e.g., Ma, Fang, Nagy, et al, ; Xu et al, ; Xu et al, ; Weber et al, ). Our result is also fully compatible with the observed SW control of the MGS‐based downward energetic electron flux (e.g., Lillis & Brain, ) and the MAVEN‐based electron impact ionization frequency (Lillis et al, ), both on the nightside of Mars.…”

Section: Variations Of Electron Depletionsmentioning

confidence: 82%

“…Near strong crustal magnetic anomalies, the preferred formation of closed magnetic loops effectively shields the atmosphere from direct access of SW electrons at all altitudes examined here (e.g., Ma et al, , ). Such a shielding should also be strongly modulated by the upstream SW condition in that under high SW dynamic pressures, the compression of the Martian magnetosphere leads to a more open magnetic field topology, which allows easier SW access to the ionosphere (e.g., Ma, Fang, Nagy, et al, ; Weber et al, ; Xu et al, , ). In weakly magnetized regions, it is likely that SW electrons are able to precipitate into the atmosphere unhindered, but their intensity is substantially reduced at low altitudes due to energy degradation via inelastic collisions with atmospheric neutrals.…”

Section: Discussionmentioning

confidence: 99%

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Energetic Electron Depletions in the Nightside Martian Upper Atmosphere Revisited

Niu

Cui

et al. 2020

JGR Space Physics

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Energetic electron depletions are a notable feature of the nightside Martian upper atmosphere. In this study, we investigate systematically the variations of the occurrence of depletions with both internal and external conditions, using the extensive Solar Wind Electron Analyzer measurements made on board the Mars Atmosphere and Volatile Evolution. In addition to the known trends of increasing occurrence with decreasing altitude and increasing magnetic field intensity, our analysis reveals that depletions are more easily observed in regions with near horizontal magnetic fields and under low solar wind (SW) dynamic pressures. We also find that below 160 km, the occurrence increases with increasing CO 2 density, a trend mostly visible in weakly magnetized regions. These observations have important implications on the formation of electron depletions: (1) Near strong magnetic anomalies, closed magnetic loops preferentially form and shield the atmosphere from direct access of SW electrons, a process that is modulated by the upstream SW condition; and (2) in weakly magnetized regions, SW electrons precipitate into the atmosphere unhindered, but at sufficiently low altitudes, they are either "absorbed" due to inelastic collisions with ambient neutrals or shielded again in response to a change in magnetic connectivity from open to closed. Our analysis further reveals that both the ionospheric plasma content and thermal electron temperature are reduced in regions with depletions compared to regions without, supporting SW electron precipitation as an important source of external energy driving the variability in the deep nightside Martian upper atmosphere and ionosphere. the Solar Wind Electron Analyzer (SWEA) on board the recent Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft (Jakosky et al., 2015). Steckiewicz et al. (2017) performed a comprehensive analysis of nightside energetic electron precipitation near Mars combining the measurements made by the Mars Global Surveyor (MGS), the Mars Express (MEx), and MAVEN, identifying more than 134,500 depletions between 125 and 900 km in altitude. The fractional

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“…Numerous instabilities can affect the structure and dynamics of the boundaries, including magnetic reconnection (Eastwood et al, 2008;, shear-related instabilities (Gunell et al, 2008;Gurnett et al, 2010;Penz et al, 2004;Ruhunusiri et al, 2016), and bi-ion instabilities (Dubinin et al, 2011;Dubinin & Sauer, 1999;Sauer et al, 1998). Crustal magnetic fields also play a role, altering the local pressure balance and constraining the transport of particles between different regions (Brain et al, 2005(Brain et al, , 2007Edberg et al, 2008;Fang et al, 2017;Garnier et al, 2017;Weber et al, 2019;Xu et al, 2016Xu et al, , 2017.…”

Section: Introductionmentioning

confidence: 99%

Ion Composition Boundary Layer Instabilities at Mars

Halekas

Ruhunusiri

McFadden

et al. 2019

Geophysical Research Letters

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The ion composition boundary layer that separates solar wind from ionospheric plasma at Mars typically contains a smooth compositional transition. However, ~10% of boundary crossings display large nonmonotonic variations in density, indicating an instability. We find that most of these instabilities occur on the flanks or downstream of the planet, and many fall into two distinct classes, which occur in different locations, under different preferred conditions. Plume events, which occur where the solar wind electric field points outward, likely represent the motion of the escaping ion plume across the spacecraft. Snowplow events, which occur where the electric field points inward, likely represent the escape of discrete parcels of plasma, which could account for ~10% of the total ion loss from Mars. Snowplow events occur under conditions that favor the development of ionospheric irregularities, which could form a seed for the snowplow mechanism that detaches and accelerates ionospheric plasma downstream.

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The Influence of Solar Wind Pressure on Martian Crustal Magnetic Field Topology

Cited by 42 publications

References 52 publications

Variations in Nightside Magnetic Field Topology at Mars

Variations in Nightside Magnetic Field Topology at Mars

Energetic Electron Depletions in the Nightside Martian Upper Atmosphere Revisited

Ion Composition Boundary Layer Instabilities at Mars

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