Statistical survey of pitch angle anisotropy of relativistic electrons in the outer radiation belt and its variation with solar wind/geomagnetic activity

Suman Chakraborty; Iain Jonathan Rae; Shannon Killey; Biswajit Ojha; Clare E. J. Watt; Charles Potts; Eleanor Irving; Gina Elliott; Katherine Johnson; Nathanial Mohammed; Tara Gupta; Thomas Slater; Xingyang Liu; Yike Cheng

doi:10.3389/fspas.2024.1474503

Statistical survey of pitch angle anisotropy of relativistic electrons in the outer radiation belt and its variation with solar wind/geomagnetic activity

Suman Chakraborty^*, Iain Jonathan Rae, Shannon Killey, Biswajit Ojha, Clare E. J. Watt, Charles Potts, Eleanor Irving, Gina Elliott, Katherine Johnson, Nathanial Mohammed, Tara Gupta, Thomas Slater, Xingyang Liu, Yike Cheng

^*Corresponding author for this work

Mathematics, Physics and Electrical Engineering

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Abstract

Introduction: In this study, we use 7 years (2012–2019) of pitch angle resolved electron flux measurements from Van Allen Probe-B spacecraft to study the variation of near-equatorial pitch angle distributions (PADs) of outer radiation belt (L <inline-formula id="inf1" style="-webkit-font-smoothing: antialiased;">≥≥</inline-formula> 3) relativistic electrons (E <inline-formula id="inf2" style="-webkit-font-smoothing: antialiased;">≥≥</inline-formula> 0.5 MeV) with different levels of geomagnetic activity.

Methods: We calculate a pitch angle anisotropy index (PAI) to categorize the PADs into three types: pancake, PAI <inline-formula id="inf3" style="-webkit-font-smoothing: antialiased;">≥≥</inline-formula> 1.05; butterfly, PAI <inline-formula id="inf4" style="-webkit-font-smoothing: antialiased;">≤≤</inline-formula> 0.95; and flattop, 0.95 <inline-formula id="inf5" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> PAI <inline-formula id="inf6" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> 1.05.

Results and Discussion: Our statistical results show that L shells <inline-formula id="inf7" style="-webkit-font-smoothing: antialiased;">≥≥</inline-formula> 5 are dominated by pancake PADs on the dayside (9 <inline-formula id="inf8" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> MLT <inline-formula id="inf9" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> 15), butterfly PADs on the nightside (21 <inline-formula id="inf10" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> MLT <inline-formula id="inf11" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> 3), and flattop PADs in the dawn (3 <inline-formula id="inf12" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> MLT <inline-formula id="inf13" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> 9) and dusk (15 <inline-formula id="inf14" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> MLT <inline-formula id="inf15" style="-webkit-font-smoothing: antialiased;"><<</inline-formula> 21) sectors, across almost all relativistic energies. In the inner L shells, the pancake and flattop PADs exhibit dependence on both L-shell and energy, with the occurrence rate increasing with decreasing L and increasing energy. For the butterfly PADs, we discovered a second population of low-L butterflies that are present at almost all local times. When the variation of electron PAI is compared with solar wind dynamic pressure <inline-formula id="inf16" style="-webkit-font-smoothing: antialiased;">PdynPdyn</inline-formula> and geomagnetic indices SYM-H and AL, <inline-formula id="inf17" style="-webkit-font-smoothing: antialiased;">PdynPdyn</inline-formula> is found to be the dominant parameter in driving the outer radiation belt pitch angle anisotropy. During periods of enhanced <inline-formula id="inf18" style="-webkit-font-smoothing: antialiased;">PdynPdyn</inline-formula>, pancake PADs on the dayside become more <inline-formula id="inf19" style="-webkit-font-smoothing: antialiased;">90°90°</inline-formula>-peaked, butterfly PADs on the nightside exhibit enhanced flux dips around <inline-formula id="inf20" style="-webkit-font-smoothing: antialiased;">90°90°</inline-formula> pitch angle along with an enhanced azimuthal and radial extent, and flattop PADs turn into either pancake or butterfly PADs.

Original language	English
Article number	1474503
Pages (from-to)	1-16
Number of pages	16
Journal	Frontiers in Astronomy and Space Sciences
Volume	11
DOIs	https://doi.org/10.3389/fspas.2024.1474503
Publication status	Published - 19 Dec 2024

Keywords

outer radiation belt
Relativistic Electrons
pitch angle distribution
Pitch angle anisotropy
Anisotropy index
Solar wind parameters
Geomagnetic indices
Van Allen Probes

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10.3389/fspas.2024.1474503Licence: CC BY

fspas-1-1474503Final published version, 72.3 MBLicence: CC BY

STFC Consolidated Grant for the Solar and Space Physics Group at Northumbria University
McLaughlin, J. (PI), Bentley, S. (CoI), Rae, J. (CoI), Jeffrey, N. (CoI), Coxon, J. (CoI) & Watt, C. (CoI)
Science and Technologies Facilities Council
1/04/23 → 31/03/26
Project: Research

Cite this

Chakraborty, S., Rae, I. J., Killey, S., Ojha, B., Watt, C. E. J., Potts, C., Irving, E., Elliott, G., Johnson, K., Mohammed, N., Gupta, T., Slater, T., Liu, X., & Cheng, Y. (2024). Statistical survey of pitch angle anisotropy of relativistic electrons in the outer radiation belt and its variation with solar wind/geomagnetic activity. Frontiers in Astronomy and Space Sciences, 11, 1-16. Article 1474503. https://doi.org/10.3389/fspas.2024.1474503

@article{1138a4184b564c54a2988ba34660cc11,

title = "Statistical survey of pitch angle anisotropy of relativistic electrons in the outer radiation belt and its variation with solar wind/geomagnetic activity",

abstract = "Introduction: In this study, we use 7 years (2012–2019) of pitch angle resolved electron flux measurements from Van Allen Probe-B spacecraft to study the variation of near-equatorial pitch angle distributions (PADs) of outer radiation belt (L ≥≥ 3) relativistic electrons (E ≥≥ 0.5 MeV) with different levels of geomagnetic activity.Methods: We calculate a pitch angle anisotropy index (PAI) to categorize the PADs into three types: pancake, PAI ≥≥ 1.05; butterfly, PAI ≤≤ 0.95; and flattop, 0.95 << PAI << 1.05.Results and Discussion: Our statistical results show that L shells ≥≥ 5 are dominated by pancake PADs on the dayside (9 << MLT << 15), butterfly PADs on the nightside (21 << MLT << 3), and flattop PADs in the dawn (3 << MLT << 9) and dusk (15 << MLT << 21) sectors, across almost all relativistic energies. In the inner L shells, the pancake and flattop PADs exhibit dependence on both L-shell and energy, with the occurrence rate increasing with decreasing L and increasing energy. For the butterfly PADs, we discovered a second population of low-L butterflies that are present at almost all local times. When the variation of electron PAI is compared with solar wind dynamic pressure PdynPdyn and geomagnetic indices SYM-H and AL, PdynPdyn is found to be the dominant parameter in driving the outer radiation belt pitch angle anisotropy. During periods of enhanced PdynPdyn, pancake PADs on the dayside become more 90°90°-peaked, butterfly PADs on the nightside exhibit enhanced flux dips around 90°90° pitch angle along with an enhanced azimuthal and radial extent, and flattop PADs turn into either pancake or butterfly PADs.",

keywords = "outer radiation belt, Relativistic Electrons, pitch angle distribution, Pitch angle anisotropy, Anisotropy index, Solar wind parameters, Geomagnetic indices, Van Allen Probes",

author = "Suman Chakraborty and Rae, {Iain Jonathan} and Shannon Killey and Biswajit Ojha and Watt, {Clare E. J.} and Charles Potts and Eleanor Irving and Gina Elliott and Katherine Johnson and Nathanial Mohammed and Tara Gupta and Thomas Slater and Xingyang Liu and Yike Cheng",

year = "2024",

month = dec,

day = "19",

doi = "10.3389/fspas.2024.1474503",

language = "English",

volume = "11",

pages = "1--16",

journal = "Frontiers in Astronomy and Space Sciences",

issn = "2296-987X",

publisher = "Frontiers Media SA",

}

Chakraborty, S , Rae, IJ , Killey, S , Ojha, B , Watt, CEJ, Potts, C, Irving, E, Elliott, G, Johnson, K, Mohammed, N, Gupta, T, Slater, T, Liu, X & Cheng, Y 2024, 'Statistical survey of pitch angle anisotropy of relativistic electrons in the outer radiation belt and its variation with solar wind/geomagnetic activity', Frontiers in Astronomy and Space Sciences, vol. 11, 1474503, pp. 1-16. https://doi.org/10.3389/fspas.2024.1474503

Statistical survey of pitch angle anisotropy of relativistic electrons in the outer radiation belt and its variation with solar wind/geomagnetic activity. / Chakraborty, Suman ; Rae, Iain Jonathan ; Killey, Shannon et al.
In: Frontiers in Astronomy and Space Sciences, Vol. 11, 1474503, 19.12.2024, p. 1-16.

Research output: Contribution to journal › Article › peer-review

TY - JOUR

T1 - Statistical survey of pitch angle anisotropy of relativistic electrons in the outer radiation belt and its variation with solar wind/geomagnetic activity

AU - Chakraborty, Suman

AU - Rae, Iain Jonathan

AU - Killey, Shannon

AU - Ojha, Biswajit

AU - Watt, Clare E. J.

AU - Potts, Charles

AU - Irving, Eleanor

AU - Elliott, Gina

AU - Johnson, Katherine

AU - Mohammed, Nathanial

AU - Gupta, Tara

AU - Slater, Thomas

AU - Liu, Xingyang

AU - Cheng, Yike

PY - 2024/12/19

Y1 - 2024/12/19

N2 - Introduction: In this study, we use 7 years (2012–2019) of pitch angle resolved electron flux measurements from Van Allen Probe-B spacecraft to study the variation of near-equatorial pitch angle distributions (PADs) of outer radiation belt (L ≥≥ 3) relativistic electrons (E ≥≥ 0.5 MeV) with different levels of geomagnetic activity.Methods: We calculate a pitch angle anisotropy index (PAI) to categorize the PADs into three types: pancake, PAI ≥≥ 1.05; butterfly, PAI ≤≤ 0.95; and flattop, 0.95 << PAI << 1.05.Results and Discussion: Our statistical results show that L shells ≥≥ 5 are dominated by pancake PADs on the dayside (9 << MLT << 15), butterfly PADs on the nightside (21 << MLT << 3), and flattop PADs in the dawn (3 << MLT << 9) and dusk (15 << MLT << 21) sectors, across almost all relativistic energies. In the inner L shells, the pancake and flattop PADs exhibit dependence on both L-shell and energy, with the occurrence rate increasing with decreasing L and increasing energy. For the butterfly PADs, we discovered a second population of low-L butterflies that are present at almost all local times. When the variation of electron PAI is compared with solar wind dynamic pressure PdynPdyn and geomagnetic indices SYM-H and AL, PdynPdyn is found to be the dominant parameter in driving the outer radiation belt pitch angle anisotropy. During periods of enhanced PdynPdyn, pancake PADs on the dayside become more 90°90°-peaked, butterfly PADs on the nightside exhibit enhanced flux dips around 90°90° pitch angle along with an enhanced azimuthal and radial extent, and flattop PADs turn into either pancake or butterfly PADs.

AB - Introduction: In this study, we use 7 years (2012–2019) of pitch angle resolved electron flux measurements from Van Allen Probe-B spacecraft to study the variation of near-equatorial pitch angle distributions (PADs) of outer radiation belt (L ≥≥ 3) relativistic electrons (E ≥≥ 0.5 MeV) with different levels of geomagnetic activity.Methods: We calculate a pitch angle anisotropy index (PAI) to categorize the PADs into three types: pancake, PAI ≥≥ 1.05; butterfly, PAI ≤≤ 0.95; and flattop, 0.95 << PAI << 1.05.Results and Discussion: Our statistical results show that L shells ≥≥ 5 are dominated by pancake PADs on the dayside (9 << MLT << 15), butterfly PADs on the nightside (21 << MLT << 3), and flattop PADs in the dawn (3 << MLT << 9) and dusk (15 << MLT << 21) sectors, across almost all relativistic energies. In the inner L shells, the pancake and flattop PADs exhibit dependence on both L-shell and energy, with the occurrence rate increasing with decreasing L and increasing energy. For the butterfly PADs, we discovered a second population of low-L butterflies that are present at almost all local times. When the variation of electron PAI is compared with solar wind dynamic pressure PdynPdyn and geomagnetic indices SYM-H and AL, PdynPdyn is found to be the dominant parameter in driving the outer radiation belt pitch angle anisotropy. During periods of enhanced PdynPdyn, pancake PADs on the dayside become more 90°90°-peaked, butterfly PADs on the nightside exhibit enhanced flux dips around 90°90° pitch angle along with an enhanced azimuthal and radial extent, and flattop PADs turn into either pancake or butterfly PADs.

KW - outer radiation belt

KW - Relativistic Electrons

KW - pitch angle distribution

KW - Pitch angle anisotropy

KW - Anisotropy index

KW - Solar wind parameters

KW - Geomagnetic indices

KW - Van Allen Probes

U2 - 10.3389/fspas.2024.1474503

DO - 10.3389/fspas.2024.1474503

M3 - Article

SN - 2296-987X

VL - 11

SP - 1

EP - 16

JO - Frontiers in Astronomy and Space Sciences

JF - Frontiers in Astronomy and Space Sciences

M1 - 1474503

ER -

Statistical survey of pitch angle anisotropy of relativistic electrons in the outer radiation belt and its variation with solar wind/geomagnetic activity

Abstract

Keywords

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Projects

STFC Consolidated Grant for the Solar and Space Physics Group at Northumbria University

Cite this