Constraining Suprathermal Electron Evolution in a Parker Spiral Field with Cassini Observations
G. A. Graham*, M. R. Bakrania, I. J. Rae, C. J. Owen, A. P. Walsh, M. J. Owens
Mathematics, Physics and Electrical Engineering
Suprathermal electrons in the solar wind consist of the "halo," present at all pitch angles, and the "strahl" which is a field-aligned, beam-like population. Examining the heliospheric evolution of strahl beams is key to understanding the in-transit processing of solar wind suprathermal electrons, in particular, to identify electron scattering mechanisms and to establish the origin of the halo population. Not only does this have significant implications with regard to the kinetic processes occurring within the solar wind but also its thermodynamic evolution, as the suprathermal electrons carry the majority of the solar wind heat flux. In this investigation, an established model for suprathermal electron evolution in a Parker spiral interplanetary magnetic field is adapted from its original use. The model is constrained using solar wind strahl observed by the Cassini mission on its interplanetary journey to Saturn. The effects of large scale IMF geometry due to different solar wind velocities and application of different electron scattering factors are examined. It is found that slow solar wind speeds provide the closest match to the strahl width observations, both in terms of radial distance and electron energy trends, and that predominantly slower solar wind speeds were therefore likely observed by the Cassini mission en-route to Saturn. It is necessary to include a strahl scattering factor which increases with electron energy in order to match observations, indicating that the strahl scattering mechanism must have an inherent energy dependence.
e2020JA028669
Journal of Geophysical Research: Space Physics
https://doi.org/10.1029/2020ja028669
10.1029/2020ja028669Licence: CC BY
2020JA028669Final published version, 867 KBLicence: CC BY
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solar wind Earth & Environmental Sciences 100%
electron Earth & Environmental Sciences 68%
Cassini mission Physics & Astronomy 46%
electrons Physics & Astronomy 41%
scattering Earth & Environmental Sciences 38%
Saturn Physics & Astronomy 33%
wind velocity Earth & Environmental Sciences 28%
halos Physics & Astronomy 25%
Graham, G. A., Bakrania, M. R., Rae, I. J., Owen, C. J., Walsh, A. P., & Owens, M. J. (2021). Constraining Suprathermal Electron Evolution in a Parker Spiral Field with Cassini Observations. Journal of Geophysical Research: Space Physics, 126(6), 1-15. [e2020JA028669]. https://doi.org/10.1029/2020ja028669
Graham, G. A. ; Bakrania, M. R. ; Rae, I. J. ; Owen, C. J. ; Walsh, A. P. ; Owens, M. J. / Constraining Suprathermal Electron Evolution in a Parker Spiral Field with Cassini Observations. In: Journal of Geophysical Research: Space Physics. 2021 ; Vol. 126, No. 6. pp. 1-15.
@article{14a8fcfa72734d14b76851a898ef0339,
title = "Constraining Suprathermal Electron Evolution in a Parker Spiral Field with Cassini Observations",
abstract = "Suprathermal electrons in the solar wind consist of the "halo," present at all pitch angles, and the "strahl" which is a field-aligned, beam-like population. Examining the heliospheric evolution of strahl beams is key to understanding the in-transit processing of solar wind suprathermal electrons, in particular, to identify electron scattering mechanisms and to establish the origin of the halo population. Not only does this have significant implications with regard to the kinetic processes occurring within the solar wind but also its thermodynamic evolution, as the suprathermal electrons carry the majority of the solar wind heat flux. In this investigation, an established model for suprathermal electron evolution in a Parker spiral interplanetary magnetic field is adapted from its original use. The model is constrained using solar wind strahl observed by the Cassini mission on its interplanetary journey to Saturn. The effects of large scale IMF geometry due to different solar wind velocities and application of different electron scattering factors are examined. It is found that slow solar wind speeds provide the closest match to the strahl width observations, both in terms of radial distance and electron energy trends, and that predominantly slower solar wind speeds were therefore likely observed by the Cassini mission en-route to Saturn. It is necessary to include a strahl scattering factor which increases with electron energy in order to match observations, indicating that the strahl scattering mechanism must have an inherent energy dependence.",
keywords = "Cassini, electrons, empirical modeling, interplanetary magnetic field, solar wind",
author = "Graham, {G. A.} and Bakrania, {M. R.} and Rae, {I. J.} and Owen, {C. J.} and Walsh, {A. P.} and Owens, {M. J.}",
note = "Funding information: G. A. Graham is supported by an ESA Research Fellowship. M. R. Bakrania was supported by the Royal Astronomical Society. I. J. Rae and C. J. Owen were supported by the STFC consolidated grant to MSSL. We thank the Cassini instrument teams, in particular the CAPS, MAG, and MIMI team members.",
doi = "10.1029/2020ja028669",
journal = "Journal of Geophysical Research - Space Physics",
Graham, GA, Bakrania, MR, Rae, IJ, Owen, CJ, Walsh, AP & Owens, MJ 2021, 'Constraining Suprathermal Electron Evolution in a Parker Spiral Field with Cassini Observations', Journal of Geophysical Research: Space Physics, vol. 126, no. 6, e2020JA028669, pp. 1-15. https://doi.org/10.1029/2020ja028669
Constraining Suprathermal Electron Evolution in a Parker Spiral Field with Cassini Observations. / Graham, G. A.; Bakrania, M. R.; Rae, I. J.; Owen, C. J.; Walsh, A. P.; Owens, M. J.
In: Journal of Geophysical Research: Space Physics, Vol. 126, No. 6, e2020JA028669, 06.2021, p. 1-15.
T1 - Constraining Suprathermal Electron Evolution in a Parker Spiral Field with Cassini Observations
AU - Graham, G. A.
AU - Bakrania, M. R.
AU - Rae, I. J.
AU - Owen, C. J.
AU - Walsh, A. P.
AU - Owens, M. J.
N1 - Funding information: G. A. Graham is supported by an ESA Research Fellowship. M. R. Bakrania was supported by the Royal Astronomical Society. I. J. Rae and C. J. Owen were supported by the STFC consolidated grant to MSSL. We thank the Cassini instrument teams, in particular the CAPS, MAG, and MIMI team members.
N2 - Suprathermal electrons in the solar wind consist of the "halo," present at all pitch angles, and the "strahl" which is a field-aligned, beam-like population. Examining the heliospheric evolution of strahl beams is key to understanding the in-transit processing of solar wind suprathermal electrons, in particular, to identify electron scattering mechanisms and to establish the origin of the halo population. Not only does this have significant implications with regard to the kinetic processes occurring within the solar wind but also its thermodynamic evolution, as the suprathermal electrons carry the majority of the solar wind heat flux. In this investigation, an established model for suprathermal electron evolution in a Parker spiral interplanetary magnetic field is adapted from its original use. The model is constrained using solar wind strahl observed by the Cassini mission on its interplanetary journey to Saturn. The effects of large scale IMF geometry due to different solar wind velocities and application of different electron scattering factors are examined. It is found that slow solar wind speeds provide the closest match to the strahl width observations, both in terms of radial distance and electron energy trends, and that predominantly slower solar wind speeds were therefore likely observed by the Cassini mission en-route to Saturn. It is necessary to include a strahl scattering factor which increases with electron energy in order to match observations, indicating that the strahl scattering mechanism must have an inherent energy dependence.
AB - Suprathermal electrons in the solar wind consist of the "halo," present at all pitch angles, and the "strahl" which is a field-aligned, beam-like population. Examining the heliospheric evolution of strahl beams is key to understanding the in-transit processing of solar wind suprathermal electrons, in particular, to identify electron scattering mechanisms and to establish the origin of the halo population. Not only does this have significant implications with regard to the kinetic processes occurring within the solar wind but also its thermodynamic evolution, as the suprathermal electrons carry the majority of the solar wind heat flux. In this investigation, an established model for suprathermal electron evolution in a Parker spiral interplanetary magnetic field is adapted from its original use. The model is constrained using solar wind strahl observed by the Cassini mission on its interplanetary journey to Saturn. The effects of large scale IMF geometry due to different solar wind velocities and application of different electron scattering factors are examined. It is found that slow solar wind speeds provide the closest match to the strahl width observations, both in terms of radial distance and electron energy trends, and that predominantly slower solar wind speeds were therefore likely observed by the Cassini mission en-route to Saturn. It is necessary to include a strahl scattering factor which increases with electron energy in order to match observations, indicating that the strahl scattering mechanism must have an inherent energy dependence.
KW - Cassini
KW - electrons
KW - empirical modeling
KW - interplanetary magnetic field
KW - solar wind
U2 - 10.1029/2020ja028669
DO - 10.1029/2020ja028669
JO - Journal of Geophysical Research - Space Physics
JF - Journal of Geophysical Research - Space Physics
M1 - e2020JA028669
Graham GA, Bakrania MR, Rae IJ, Owen CJ, Walsh AP, Owens MJ. Constraining Suprathermal Electron Evolution in a Parker Spiral Field with Cassini Observations. Journal of Geophysical Research: Space Physics. 2021 Jun;126(6):1-15. e2020JA028669. https://doi.org/10.1029/2020ja028669