Journal article
Rapid enhancement of low‐energy (<100 eV) ion flux in response to interplanetary shocks based on two Van Allen Probes case studies: Implications for source regions and heating mechanisms
Journal of geophysical research. Space physics, Vol.121(7), pp.6430-6443
07/2016
DOI: 10.1002/2016JA022808
Abstract
Interactions between interplanetary (IP) shocks and the Earth's magnetosphere manifest many important space physics phenomena including low‐energy ion flux enhancements and particle acceleration. In order to investigate the mechanisms driving shock‐induced enhancement of low‐energy ion flux, we have examined two IP shock events that occurred when the Van Allen Probes were located near the equator while ionospheric and ground observations were available around the spacecraft footprints. We have found that, associated with the shock arrival, electromagnetic fields intensified, and low‐energy ion fluxes, including H+, He+, and O+, were enhanced dramatically in both the parallel and perpendicular directions. During the 2 October 2013 shock event, both parallel and perpendicular flux enhancements lasted more than 20 min with larger fluxes observed in the perpendicular direction. In contrast, for the 15 March 2013 shock event, the low‐energy perpendicular ion fluxes increased only in the first 5 min during an impulse of electric field, while the parallel flux enhancement lasted more than 30 min. In addition, ionospheric outflows were observed after shock arrivals. From a simple particle motion calculation, we found that the rapid response of low‐energy ions is due to drifts of plasmaspheric population by the enhanced electric field. However, the fast acceleration in the perpendicular direction cannot solely be explained by E × B drift but betatron acceleration also plays a role. Adiabatic acceleration may also explain the fast response of the enhanced parallel ion fluxes, while ion outflows may contribute to the enhanced parallel fluxes that last longer than the perpendicular fluxes.
Key Points
The low‐energy ion fluxes were enhanced dramatically in both the parallel and perpendicular directions after the shock arrivals
The rapid response of low‐energy ions is due to drifts of plasmaspheric population by the enhanced electric field
Ion outflows contribute to the enhanced parallel population that last longer than the perpendicular population
Details
- Title: Subtitle
- Rapid enhancement of low‐energy (<100 eV) ion flux in response to interplanetary shocks based on two Van Allen Probes case studies: Implications for source regions and heating mechanisms
- Creators
- Chao Yue - University Corporation for Atmospheric ResearchWen Li - University of California, Los AngelesYukitoshi Nishimura - University of California, Los AngelesQiugang Zong - Peking UniversityQianli Ma - University of California, Los AngelesJacob Bortnik - University of California, Los AngelesRichard M Thorne - University of California, Los AngelesGeoffrey D Reeves - Los Alamos National LaboratoryHarlan E Spence - University of New HampshireCraig A Kletzing - University of IowaJohn R Wygant - University of MinnesotaMichael J Nicolls - SRI International
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.121(7), pp.6430-6443
- DOI
- 10.1002/2016JA022808
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 14
- Grant note
- NSF (PLR‐1341359; AGS‐1405054; 1564510) AFOSR (FA9550‐15‐1‐0179) NASA (NNX15AI62G; NNX13AI61G; NNX14AI18G)
- Language
- English
- Date published
- 07/2016
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984199711102771
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