ULF Wave Driven Radial Diffusion During Geomagnetic Storms: A statistical analysis of Van Allen Probes observations

Sandhu, Jasmine, Rae, Jonathan, Wygant, J. R., Breneman, A. W., Tian, S., Watt, Clare, Horne, R. B., Ozeke, L. G., Georgiou, M. and Walach, M.‐T. (2021) ULF Wave Driven Radial Diffusion During Geomagnetic Storms: A statistical analysis of Van Allen Probes observations. Journal of Geophysical Research: Space Physics, 126 (4). e2020JA029024. ISSN 2169-9380

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Official URL: https://doi.org/10.1029/2020ja029024

Abstract

The impact of radial diffusion in storm time radiation belt dynamics is well‐debated. In this study we quantify the changes and variability in radial diffusion coefficients during geomagnetic storms. A statistical analysis of Van Allen Probes data (2012 − 2019) is conducted to obtain measurements of the magnetic and electric power spectral densities for Ultra Low Frequency (ULF) waves, and corresponding radial diffusion coefficients. The results show global wave power enhancements occur during the storm main phase, and continue into the recovery phase. Local time asymmetries show sources of wave power are both external solar wind driving and internal sources from coupling with ring current ions and substorms. Wave power enhancements are also observed at low L values (L < 4). The accessibility of wave power to low L is attributed to a depression of the Alfvén continuum. The increased wave power drives enhancements in both the magnetic and electric field diffusion coefficients by more than an order of magnitude. Significant variability in diffusion coefficients is observed, with values ranging over several orders of magnitude. A comparison to the Kp parameterised empirical model of Ozeke et al. (2014) is conducted and indicates important differences during storm times. Although the electric field diffusion coefficient is relatively well described by the empirical model, the magnetic field diffusion coefficient is approximately ∼ 10 times larger than predicted. We discuss how differences could be attributed to dataset limitations and assumptions. Alternative storm‐time radial diffusion coefficients are provided as a function of L* and storm phase.

Item Type: Article
Additional Information: Funding information: J. K. S. was supported by NERC Grants NE/P017185/1 and NE/V002554/1. I. J. R. was supported by NERC Grants NE/P017185/1 and NE/V002554/1. R. B. H. was supported by Highlight Topic Grant NE/P01738X/1 (Rad-Sat). M.-T. W was supported by Natural Environments Research Council grants NE/P001556/1 and NE/T000937/1. We thank the EMFISIS instrument team for data provision. We thank the EFW team for data provision and the work by the EFW team was conducted under JHU/APL contract 922613 (RBSP-EFW). The Van Allen Probes data is publicly available online (https://cdaweb.gsfc.nasa.gov/index.html/). The solar wind data and Sym-H index data are publicly available online (http://wdc.kugi.kyoto-u.ac.jp/index.html).
Uncontrolled Keywords: ULF waves, Radial Diffusion, Outer Radiation Belt, Van Allen Probes, Geomagnetic Storms
Subjects: F300 Physics
F500 Astronomy
F800 Physical and Terrestrial Geographical and Environmental Sciences
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Elena Carlaw
Date Deposited: 26 Mar 2021 10:42
Last Modified: 08 Apr 2021 12:24
URI: http://nrl.northumbria.ac.uk/id/eprint/45800

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