Statistical investigation on equatorial pitch angle distribution of energetic electrons in Earth’s outer radiation belt during CME- and CIR-driven storms

Chakraborty, Suman, Chakrabarty, Dibyendu, Reeves, Geoffrey D., Baker, Daniel N. and Rae, Jonathan (2022) Statistical investigation on equatorial pitch angle distribution of energetic electrons in Earth’s outer radiation belt during CME- and CIR-driven storms. Frontiers in Astronomy and Space Sciences, 9. p. 986061. ISSN 2296-987X

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Official URL: https://doi.org/10.3389/fspas.2022.986061

Abstract

We present a statistical investigation (September 2012 - September 2017) of pitch angle distribution (PAD) of energetic electrons (~30 keV - 1 MeV) in the outer radiation belt (L > 3) during CME- and CIR-driven geomagnetic storms using Van Allen Probe measurements. We selected geomagnetic storms based on minimum of SYM-H being less than -50 nT and classified the storms according to their drivers. Thus, we obtained 23 CME- and 24 CIR-driven storms. During the storm intervals, pitch angle resolved electron flux measurements are obtained from the MagEIS instrument on-board Van Allen Probe-A spacecraft. We assume symmetric pitch angle distributions around 90 degree pitch angle and fit the observed PADs with Legendre polynomials after propagating them to the magnetic equator. Legendre coefficients c2 and c4, and the ratio R = |c2/c4| are used to categorize the different PAD types. To resolve the spatio-temporal distribution of PADs, these coefficients are binned in 6 L-shell bins, 13 MLT bins for 7 energy channels and 4 storm phases. We found that several hundreds of keV electrons exhibit clear dependence on local time, storm phases and storm drivers, with increased anisotropy for CME-driven storms during main and early recovery phases. On the contrary, we found that tens of keV electrons do not exhibit significant dependence on these parameters. We have discussed the different physical mechanisms responsible for the observed MLT dependent PADs and found drift-shell splitting to be the major contributor.

Item Type: Article
Additional Information: Funding information: SC is supported in part by STFC Grant ST/V006320/1 and NERC Grants NE/V002554/2 and NE/P017185/2, and in part by the Department of Space, Government of India. DC is supported by the Department of Space, Government of India. IJR is supported in part by STFC Grant ST/V006320/1 and NERC Grants NE/V002554/2 and NE/P017185/2.
Uncontrolled Keywords: pitch angle distribution, outer radiation belt, energetic electrons, van allen probes, geomagnetic storms, CME, CIR
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Elena Carlaw
Date Deposited: 08 Aug 2022 12:34
Last Modified: 30 Aug 2022 08:15
URI: https://nrl.northumbria.ac.uk/id/eprint/49766

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