Radiation belt electron acceleration during the 17 March 2015 geomagnetic storm: Observations and simulations

• Published in: Journal of geophysical research. Space physics 2016-06, Vol.121 (6), p.5520-5536
• Main Authors: Li, W., Ma, Q., Thorne, R. M., Bortnik, J., Zhang, X.‐J., Li, J., Baker, D. N., Reeves, G. D., Spence, H. E., Kletzing, C. A., Kurth, W. S., Hospodarsky, G. B., Blake, J. B., Fennell, J. F., Kanekal, S. G., Angelopoulos, V., Green, J. C., Goldstein, J.
• Format: Article
• Language: English
• Subjects: Acceleration; Belt conveyors; Chorus; chorus-driven local acceleration; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Diffusion; Diffusion theory; Dynamic tests; Electron acceleration; Electron density; Electron flux; Electrons; Evolution; Geomagnetic storms; Geomagnetism; Geophysics; GEOSCIENCES; Heliospheric and Magnetospheric Physics; Hiss; Magnetic storms; Pitch (inclination); Pitch angle; radial diffusion; Radiation; Radiation belts; Scattering; Simulation; Storms
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2016JA022400

Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3‐D diffusion simulation. By quantitatively comparing the observed and simulated electron evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak location and produces characteristic flat‐top pitch angle distributions. By only including radial diffusion, the simulation underestimates the observed electron acceleration, while radial diffusion plays an important role in redistributing electrons and potentially accelerates them to even higher energies. Moreover, plasmaspheric hiss is found to provide efficient pitch angle scattering losses for hundreds of keV electrons, while its scattering effect on > 1 MeV electrons is relatively slow. Although an additional loss process is required to fully explain the overestimated electron fluxes at multi‐MeV, the combined physical processes of radial diffusion and pitch angle and energy diffusion by chorus and hiss reproduce the observed electron dynamics remarkably well, suggesting that quasi‐linear diffusion theory is reasonable to evaluate radiation belt electron dynamics during this big storm. Key Points Radiation belt electrons experienced rapid acceleration up to multi‐MeV during 17 March 2015 storm Chorus plays an important role in accelerating electrons to multi‐MeV near PSD peak location Radial diffusion is critical in redistributing electrons and could provide further acceleration