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ORIGINAL RESEARCH article

Front. Astron. Space Sci.
Sec. Space Physics
Volume 11 - 2024 | doi: 10.3389/fspas.2024.1474503
This article is part of the Research Topic The Loss and Acceleration Mechanisms of Energetic Electrons in the Earth’s Outer Radiation Belt View all 9 articles

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

Provisionally accepted
Suman Chakraborty Suman Chakraborty *Jonathan Rae Jonathan Rae Shannon Killey Shannon Killey Biswajit Ojha Biswajit Ojha Clare E J Watt Clare E J Watt
  • Northumbria University, Newcastle upon Tyne, United Kingdom

The final, formatted version of the article will be published soon.

    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. 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. 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 P dyn and geomagnetic indices SYM-H and AL, P dyn is found to be the dominant parameter in driving the outer radiation belt pitch angle anisotropy. During periods of enhanced P dyn , pancake PADs on the dayside become more 90 • -peaked, butterfly PADs on the nightside exhibit enhanced flux dips around 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

    Received: 01 Aug 2024; Accepted: 21 Nov 2024.

    Copyright: © 2024 Chakraborty, Rae, Killey, Ojha and Watt. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Suman Chakraborty, Northumbria University, Newcastle upon Tyne, United Kingdom

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