Contributions to the magnetospheric parallel electric field

Craig R. Stark, A. P. Cran-McGreehin, A. N. Wright

Research output: Contribution to journalArticle

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Abstract

[1] Upward field-aligned currents and their associated parallel electric fields couple the ionosphere to the magnetosphere. It is desirable to know how such a potential drop is distributed along the flux tube, what controls its variation, and how it is balanced by the plasma. By considering the motion of the ionospheric and magnetospheric electrons and ions, under the influence of electrostatic and magnetic mirror forces, a quasi steady state, quasi-neutral electric field distribution along the magnetic flux tube can be obtained. A feature of the potential profiles is the occurrence of a potential jump that splits the profile into three distinct regions: below the jump, within the jump, and above the jump. Within a kinetic framework, we analyze how the plasma velocity distributions evolve along the flux tube, taking into account ionospheric, magnetospheric, mirroring, and precipitating electron populations. By calculating the moments of the governing Vlasov equation, we ascertain what balances the parallel electric field (E∥) and how it is maintained, establishing a dynamical equilibrium. Our calculations show that (1) earthward of the jump E∥ ≈ −(p⊥/enB)∇∥B associated with the ionospheric electrons, except for at the base of the F region where p∥ contributions become more significant; (2) within the jump magnetosphere electrons dominate and E∥ ≈ −(1/en)∇∥p∥; and (3) above the jump mirroring magnetospheric electrons make a principal contribution of E∥ ≈ −(1/en)∇∥p∥, with a secondary contribution of −(p⊥ − p∥)∇∥B/(ne) becoming comparable beyond ≈3 RE. Additionally, we found that although the precipitating electrons carry the field-aligned current, it is the mirroring population that determines where E∥ is concentrated and hence where precipitating electrons are accelerated.
Original languageEnglish
Number of pages13
JournalJournal of Geophysical Research: Space Physics
Volume116
Issue numberA7
DOIs
Publication statusPublished - 20 Jul 2011

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electric fields
electrons
ionospherics
field aligned currents
tubes
magnetospheres
magnetic mirrors
vlasov equations
quasi-steady states
F region
profiles
ionospheres
magnetic flux
velocity distribution
occurrences
electrostatics
mirrors
moments
kinetics
ions

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title = "Contributions to the magnetospheric parallel electric field",
abstract = "[1] Upward field-aligned currents and their associated parallel electric fields couple the ionosphere to the magnetosphere. It is desirable to know how such a potential drop is distributed along the flux tube, what controls its variation, and how it is balanced by the plasma. By considering the motion of the ionospheric and magnetospheric electrons and ions, under the influence of electrostatic and magnetic mirror forces, a quasi steady state, quasi-neutral electric field distribution along the magnetic flux tube can be obtained. A feature of the potential profiles is the occurrence of a potential jump that splits the profile into three distinct regions: below the jump, within the jump, and above the jump. Within a kinetic framework, we analyze how the plasma velocity distributions evolve along the flux tube, taking into account ionospheric, magnetospheric, mirroring, and precipitating electron populations. By calculating the moments of the governing Vlasov equation, we ascertain what balances the parallel electric field (E∥) and how it is maintained, establishing a dynamical equilibrium. Our calculations show that (1) earthward of the jump E∥ ≈ −(p⊥/enB)∇∥B associated with the ionospheric electrons, except for at the base of the F region where p∥ contributions become more significant; (2) within the jump magnetosphere electrons dominate and E∥ ≈ −(1/en)∇∥p∥; and (3) above the jump mirroring magnetospheric electrons make a principal contribution of E∥ ≈ −(1/en)∇∥p∥, with a secondary contribution of −(p⊥ − p∥)∇∥B/(ne) becoming comparable beyond ≈3 RE. Additionally, we found that although the precipitating electrons carry the field-aligned current, it is the mirroring population that determines where E∥ is concentrated and hence where precipitating electrons are accelerated.",
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Contributions to the magnetospheric parallel electric field. / Stark, Craig R.; Cran-McGreehin, A. P.; Wright, A. N.

In: Journal of Geophysical Research: Space Physics, Vol. 116, No. A7, 20.07.2011.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Contributions to the magnetospheric parallel electric field

AU - Stark, Craig R.

AU - Cran-McGreehin, A. P.

AU - Wright, A. N.

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N2 - [1] Upward field-aligned currents and their associated parallel electric fields couple the ionosphere to the magnetosphere. It is desirable to know how such a potential drop is distributed along the flux tube, what controls its variation, and how it is balanced by the plasma. By considering the motion of the ionospheric and magnetospheric electrons and ions, under the influence of electrostatic and magnetic mirror forces, a quasi steady state, quasi-neutral electric field distribution along the magnetic flux tube can be obtained. A feature of the potential profiles is the occurrence of a potential jump that splits the profile into three distinct regions: below the jump, within the jump, and above the jump. Within a kinetic framework, we analyze how the plasma velocity distributions evolve along the flux tube, taking into account ionospheric, magnetospheric, mirroring, and precipitating electron populations. By calculating the moments of the governing Vlasov equation, we ascertain what balances the parallel electric field (E∥) and how it is maintained, establishing a dynamical equilibrium. Our calculations show that (1) earthward of the jump E∥ ≈ −(p⊥/enB)∇∥B associated with the ionospheric electrons, except for at the base of the F region where p∥ contributions become more significant; (2) within the jump magnetosphere electrons dominate and E∥ ≈ −(1/en)∇∥p∥; and (3) above the jump mirroring magnetospheric electrons make a principal contribution of E∥ ≈ −(1/en)∇∥p∥, with a secondary contribution of −(p⊥ − p∥)∇∥B/(ne) becoming comparable beyond ≈3 RE. Additionally, we found that although the precipitating electrons carry the field-aligned current, it is the mirroring population that determines where E∥ is concentrated and hence where precipitating electrons are accelerated.

AB - [1] Upward field-aligned currents and their associated parallel electric fields couple the ionosphere to the magnetosphere. It is desirable to know how such a potential drop is distributed along the flux tube, what controls its variation, and how it is balanced by the plasma. By considering the motion of the ionospheric and magnetospheric electrons and ions, under the influence of electrostatic and magnetic mirror forces, a quasi steady state, quasi-neutral electric field distribution along the magnetic flux tube can be obtained. A feature of the potential profiles is the occurrence of a potential jump that splits the profile into three distinct regions: below the jump, within the jump, and above the jump. Within a kinetic framework, we analyze how the plasma velocity distributions evolve along the flux tube, taking into account ionospheric, magnetospheric, mirroring, and precipitating electron populations. By calculating the moments of the governing Vlasov equation, we ascertain what balances the parallel electric field (E∥) and how it is maintained, establishing a dynamical equilibrium. Our calculations show that (1) earthward of the jump E∥ ≈ −(p⊥/enB)∇∥B associated with the ionospheric electrons, except for at the base of the F region where p∥ contributions become more significant; (2) within the jump magnetosphere electrons dominate and E∥ ≈ −(1/en)∇∥p∥; and (3) above the jump mirroring magnetospheric electrons make a principal contribution of E∥ ≈ −(1/en)∇∥p∥, with a secondary contribution of −(p⊥ − p∥)∇∥B/(ne) becoming comparable beyond ≈3 RE. Additionally, we found that although the precipitating electrons carry the field-aligned current, it is the mirroring population that determines where E∥ is concentrated and hence where precipitating electrons are accelerated.

U2 - 10.1029/2010JA016270

DO - 10.1029/2010JA016270

M3 - Article

VL - 116

JO - Journal of Geophysical Research: Space Physics

JF - Journal of Geophysical Research: Space Physics

SN - 2169-9402

IS - A7

ER -