Anisotropic kinetic effects of photoelectrons on polar wind transport

Sunny Wing-Yee Tam, Fareed Yasseen, Tom Chang, Supriya B. Ganguli, John M. Retterer

Research output: Chapter in Book/Report/Conference proceedingChapter

4 Citations (Scopus)

Abstract

There is increasing observational evidence that photoelectrons may affect polar wind dynamics. For example, suprathermal electron pitch-angle distributions in the photoelectron energy range have been observed in the high-altitude polar wind. These distributions contribute little to the polar wind density, but carry an appreciable outward heat flux. Evidence of such reflected photoelectron distributions at low altitudes have been attributed to field-aligned potential drop. More recently, measurements of day-night asymmetries in electron temperature and ion outflow provide further indications of the photoelectrons’ impact on the polar wind. Such non-thermal fluxes can be explained by a mechanism relying on the earth’s decreasing magnetic field, the field-aligned potential drop, and the energy dependence of the Coulomb collisional cross-sections. The description of this mechanism requires a kinetic approach. Such an approach was used in a testparticle simulation of this mechanism, in agreement with the measured suprathermal fluxes. However, the effects of these fluxes on the polar wind itself require a self-consistent description. Unfortunately, a fully kinetic self-consistent description is at present not achievable. Instead, we suggest a hybrid approach, in which the background features of the polar wind are described by well-established fluid models, while the suprathermal features are described using a kinetic model. This approach retains the expediency of fluid theory while in effect extending its applicability. In this paper, we will review the physics underlying the mechanism mentioned earlier, discuss how the kinetic-fluid synthesis can best be achieved, and present our latest results. Our initial calculations show, for example, that the suprathermal electrons carry much of the polar wind heat flux, and may significantly increase the ambipolar electric field. This increase in the electric field can change the dynamics of the polar wind outflow.

Original languageEnglish
Title of host publicationCross-Scale Coupling in Space Plasmas, 1995
EditorsJames L. Horwitz, Nagendra Singh, James L. Burch
PublisherBlackwell Publishing Ltd
Pages133-139
Number of pages7
ISBN (Electronic)9781118664278
ISBN (Print)9780875900759
DOIs
Publication statusPublished - 1995 Jan 1

Publication series

NameGeophysical Monograph Series
Volume93
ISSN (Print)0065-8448
ISSN (Electronic)2328-8779

Fingerprint

photoelectrons
kinetics
potential field
electron
heat flux
fluid
electric field
fluids
outflow
electric fields
effect
low altitude
pitch (inclination)
high altitude
night
energy
asymmetry
indication
electrons
physics

All Science Journal Classification (ASJC) codes

  • Geophysics

Cite this

Tam, S. W-Y., Yasseen, F., Chang, T., Ganguli, S. B., & Retterer, J. M. (1995). Anisotropic kinetic effects of photoelectrons on polar wind transport. In J. L. Horwitz, N. Singh, & J. L. Burch (Eds.), Cross-Scale Coupling in Space Plasmas, 1995 (pp. 133-139). (Geophysical Monograph Series; Vol. 93). Blackwell Publishing Ltd. https://doi.org/10.1029/GM093p0133
Tam, Sunny Wing-Yee ; Yasseen, Fareed ; Chang, Tom ; Ganguli, Supriya B. ; Retterer, John M. / Anisotropic kinetic effects of photoelectrons on polar wind transport. Cross-Scale Coupling in Space Plasmas, 1995. editor / James L. Horwitz ; Nagendra Singh ; James L. Burch. Blackwell Publishing Ltd, 1995. pp. 133-139 (Geophysical Monograph Series).
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Tam, SW-Y, Yasseen, F, Chang, T, Ganguli, SB & Retterer, JM 1995, Anisotropic kinetic effects of photoelectrons on polar wind transport. in JL Horwitz, N Singh & JL Burch (eds), Cross-Scale Coupling in Space Plasmas, 1995. Geophysical Monograph Series, vol. 93, Blackwell Publishing Ltd, pp. 133-139. https://doi.org/10.1029/GM093p0133

Anisotropic kinetic effects of photoelectrons on polar wind transport. / Tam, Sunny Wing-Yee; Yasseen, Fareed; Chang, Tom; Ganguli, Supriya B.; Retterer, John M.

Cross-Scale Coupling in Space Plasmas, 1995. ed. / James L. Horwitz; Nagendra Singh; James L. Burch. Blackwell Publishing Ltd, 1995. p. 133-139 (Geophysical Monograph Series; Vol. 93).

Research output: Chapter in Book/Report/Conference proceedingChapter

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AU - Tam, Sunny Wing-Yee

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PY - 1995/1/1

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N2 - There is increasing observational evidence that photoelectrons may affect polar wind dynamics. For example, suprathermal electron pitch-angle distributions in the photoelectron energy range have been observed in the high-altitude polar wind. These distributions contribute little to the polar wind density, but carry an appreciable outward heat flux. Evidence of such reflected photoelectron distributions at low altitudes have been attributed to field-aligned potential drop. More recently, measurements of day-night asymmetries in electron temperature and ion outflow provide further indications of the photoelectrons’ impact on the polar wind. Such non-thermal fluxes can be explained by a mechanism relying on the earth’s decreasing magnetic field, the field-aligned potential drop, and the energy dependence of the Coulomb collisional cross-sections. The description of this mechanism requires a kinetic approach. Such an approach was used in a testparticle simulation of this mechanism, in agreement with the measured suprathermal fluxes. However, the effects of these fluxes on the polar wind itself require a self-consistent description. Unfortunately, a fully kinetic self-consistent description is at present not achievable. Instead, we suggest a hybrid approach, in which the background features of the polar wind are described by well-established fluid models, while the suprathermal features are described using a kinetic model. This approach retains the expediency of fluid theory while in effect extending its applicability. In this paper, we will review the physics underlying the mechanism mentioned earlier, discuss how the kinetic-fluid synthesis can best be achieved, and present our latest results. Our initial calculations show, for example, that the suprathermal electrons carry much of the polar wind heat flux, and may significantly increase the ambipolar electric field. This increase in the electric field can change the dynamics of the polar wind outflow.

AB - There is increasing observational evidence that photoelectrons may affect polar wind dynamics. For example, suprathermal electron pitch-angle distributions in the photoelectron energy range have been observed in the high-altitude polar wind. These distributions contribute little to the polar wind density, but carry an appreciable outward heat flux. Evidence of such reflected photoelectron distributions at low altitudes have been attributed to field-aligned potential drop. More recently, measurements of day-night asymmetries in electron temperature and ion outflow provide further indications of the photoelectrons’ impact on the polar wind. Such non-thermal fluxes can be explained by a mechanism relying on the earth’s decreasing magnetic field, the field-aligned potential drop, and the energy dependence of the Coulomb collisional cross-sections. The description of this mechanism requires a kinetic approach. Such an approach was used in a testparticle simulation of this mechanism, in agreement with the measured suprathermal fluxes. However, the effects of these fluxes on the polar wind itself require a self-consistent description. Unfortunately, a fully kinetic self-consistent description is at present not achievable. Instead, we suggest a hybrid approach, in which the background features of the polar wind are described by well-established fluid models, while the suprathermal features are described using a kinetic model. This approach retains the expediency of fluid theory while in effect extending its applicability. In this paper, we will review the physics underlying the mechanism mentioned earlier, discuss how the kinetic-fluid synthesis can best be achieved, and present our latest results. Our initial calculations show, for example, that the suprathermal electrons carry much of the polar wind heat flux, and may significantly increase the ambipolar electric field. This increase in the electric field can change the dynamics of the polar wind outflow.

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Tam SW-Y, Yasseen F, Chang T, Ganguli SB, Retterer JM. Anisotropic kinetic effects of photoelectrons on polar wind transport. In Horwitz JL, Singh N, Burch JL, editors, Cross-Scale Coupling in Space Plasmas, 1995. Blackwell Publishing Ltd. 1995. p. 133-139. (Geophysical Monograph Series). https://doi.org/10.1029/GM093p0133