Constraining the Location of the Outer Boundary of Earth's Outer Radiation Belt

Bloch, T., Watt, Clare, Owens, M. J., Thompson, R. L. and Agiwal, O. (2021) Constraining the Location of the Outer Boundary of Earth's Outer Radiation Belt. Earth and Space Science, 8 (6). e2020EA001610. ISSN 2333-5084

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Characterizing the location of the outer boundary of the outer radiation belt is a key aspect of improving radiation belt models and helps to constrain our understanding of the mechanisms by which the source and seed electron populations are transported into the radiation belts. In this paper, we hypothesize that there are statistical differences in the electron distribution function across the radiation belt outer boundary, and thus analyze electron flux data from the THEMIS (Time History of Events and Macroscale Interactions during Substorms) satellites to identify this location. We validate our hypothesis by using modeled electron L* values to approximately characterize the differences between electron distribution functions inside and outside of the radiation belts. Initially, we perform a simple statistical analysis by studying the radial evolution of the electron distribution functions. This approach does not yield a clear discontinuity, thus highlighting the need for more complex statistical treatment of the data. Subsequently, we employ machine learning (with no dependence on radial position or L*) to test a range of candidate outer boundary locations. By analyzing the performance of the models at each candidate location, we identify a statistical boundary at ≈8 RE, with results suggesting some variability. This statistical boundary is typically further out than those used in current radiation belt models.

Item Type: Article
Additional Information: Funding information: We acknowledge the NASA National Space Science Data Center and the Space Physics Data Facility for usage of THEMIS data. We acknowledge D. Boscher, S. Bourdarie, P. O'Brien and T. Guild for the IRBEM library V4.3, 2004–2008 ( and J. Koller and S. Morley for the python interface of IRBEM in SpacePy. Téo Bloch is funded by Science and Technology Facilities Council (STFC) training grant number ST/R505031/1. Clare Watt is part funded by STFC grant number ST/R000921/1 and Natural Environment Research Council (NERC) grant number NE/P017274/1. Mathew Owens is part-funded by STFC grant number ST/R000921/1 and NERC grant number NE/P016928/1. Rhys Thompson is funded by Engineering and Physical Sciences Research Council (EPSRC) grant number EP/L016613/1. Omakshi Agiwal is funded by Science and Technology Facilities Council (STFC) training grant number ST/R504816/1.
Uncontrolled Keywords: Radiation Belts, Machine Learning, THEMIS, Empirical Boundary, Outer Boundary
Subjects: F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: John Coen
Date Deposited: 01 Jun 2021 14:50
Last Modified: 31 Jul 2021 10:50

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