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
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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jul 01, 2016
- Source ID
- 10.1002/2016ja022808
Entities
People
- Chao Yue
- Craig Kletzing
- Geoffrey D Reeves
- Harlan Spence
- Jacob Bortnik
- John R. Wygant
- Michael J. Nicolls
- Qianli Ma
- Qiugang Zong
- Richard M. Thorne
- Wen Li
- Yukitoshi Nishimura
Organizations
- Air Force Office of Scientific Research
- Los Alamos National Laboratory
- National Aeronautics and Space Administration
- National Science Foundation
- Peking University
- SRI International
- University Corporation for Atmospheric Research
- University of California, Los Angeles
- University of Iowa
- University of Minnesota
- University of New Hampshire