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Title: 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. Furthermore,more » 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.« less

Authors:
 [1];  [2];  [3];  [2];  [4];  [2];  [2];  [2];  [5];  [6];  [7];  [8]
  1. UCLA, Los Angeles, CA (United States); Univ. Corp. for Atmospheric Research, Boulder, CO (United States)
  2. UCLA, Los Angeles, CA (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); New Mexico Consortium, Los Alamos, NM (United States)
  4. Peking Univ., Beijing (China)
  5. Univ. of New Hampshire, Durham, NH (United States)
  6. Univ. of Iowa, Iowa City, IA (United States)
  7. Univ. of Minnesota, Minneapolis, MN (United States)
  8. SRI International, Menlo Park, CA (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
National Aeronautic and Space Administration (NASA); USDOE
OSTI Identifier:
1291234
Report Number(s):
LA-UR-16-23136
Journal ID: ISSN 2169-9380
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Name: Journal of Geophysical Research. Space Physics; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Heliospheric and Magnetospheric Physics

Citation Formats

Yue, Chao, Li, Wen, Reeves, Geoffrey D., Nishimura, Yukitoshi, Zong, Qiugang, Ma, Qianli, Bortnik, Jacob, Thorne, Richard M., Spence, Harlan E., Kletzing, Craig A., Wygant, John R., and Nicolls, Michael J.. 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. United States: N. p., 2016. Web. doi:10.1002/2016JA022808.
Yue, Chao, Li, Wen, Reeves, Geoffrey D., Nishimura, Yukitoshi, Zong, Qiugang, Ma, Qianli, Bortnik, Jacob, Thorne, Richard M., Spence, Harlan E., Kletzing, Craig A., Wygant, John R., & Nicolls, Michael J.. 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. United States. doi:10.1002/2016JA022808.
Yue, Chao, Li, Wen, Reeves, Geoffrey D., Nishimura, Yukitoshi, Zong, Qiugang, Ma, Qianli, Bortnik, Jacob, Thorne, Richard M., Spence, Harlan E., Kletzing, Craig A., Wygant, John R., and Nicolls, Michael J.. 2016. "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". United States. doi:10.1002/2016JA022808. https://www.osti.gov/servlets/purl/1291234.
@article{osti_1291234,
title = {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},
author = {Yue, Chao and Li, Wen and Reeves, Geoffrey D. and Nishimura, Yukitoshi and Zong, Qiugang and Ma, Qianli and Bortnik, Jacob and Thorne, Richard M. and Spence, Harlan E. and Kletzing, Craig A. and Wygant, John R. and Nicolls, Michael J.},
abstractNote = {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. Furthermore, 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.},
doi = {10.1002/2016JA022808},
journal = {Journal of Geophysical Research. Space Physics},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 7
}

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  • Enabled by the comprehensive measurements from the Magnetic Electron Ion Spectrometer (MagEIS), Helium Oxygen Proton Electron mass spectrometer (HOPE), and Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instruments onboard Van Allen Probes in the heart of the radiation belt, the relative contributions of ions with different energies and species to the ring current energy density and their dependence on the phases of geomagnetic storms are quantified. The results show that lower energy (<50 keV) protons enhance much more often and also decay much faster than higher-energy protons. During the storm main phase, ions with energies <50 keV contribute moremore » significantly to the ring current than those with higher energies; while the higher-energy protons dominate during the recovery phase and quiet times. The enhancements of higher-energy proton fluxes as well as energy content generally occur later than those of lower energy protons, which could be due to the inward radial diffusion. For the 29 March 2013 storm we investigated in detail that the contribution from O + is ~25% of the ring current energy content during the main phase and the majority of that comes from <50 keV O +. This indicates that even during moderate geomagnetic storms the ionosphere is still an important contributor to the ring current ions. Using the Dessler-Parker-Sckopke relation, the contributions of ring current particles to the magnetic field depression during this geomagnetic storm are also calculated. In conclusion, the results show that the measured ring current ions contribute about half of the Dst depression.« less
  • Understanding the dynamical behavior of ~1 eV to 50 keV ions and identifying the energies at which the morphologies transit are important in that they involve the relative intensities and distributions of the large-scale electric and magnetic fields, the outflow, and recombination rates. However, there have been only few direct observational investigations of the transition in drift behaviors of different energy ions before the Van Allen Probes era. In this paper, we statistically analyze ~1 eV to 50 keV hydrogen (H +) differential flux distributions near geomagnetic equator by using Van Allen Probes observations to investigate the H + dynamicsmore » under the regulation of large-scale electric and magnetic fields. Our survey clearly indicates three types of H + behaviors within different energy ranges, which is consistent with previous theory predictions. Finally, using simple electric and magnetic field models in UBK coordinates, we have further constrained the source regions of different energy ions and their drift directions.« less
  • On 23 November 2012, a sudden dropout of the relativistic electron flux was observed after an interplanetary shock arrival. The dropout peaks at ~1 MeV and more than 80% of the electrons disappeared from the drift shell. Van Allen twin Probes observed a sharp electron flux dropout with clear energy dispersion signals. The repeating flux dropout and recovery signatures, or “dropout echoes”, constitute a new phenomenon referred to as a “drifting electron dropout” with a limited initial spatial range. The azimuthal range of the dropout is estimated to be on the duskside, from ~1300 to 0100 LT. We then concludemore » that the shock-induced electron dropout is not caused by the magnetopause shadowing. Furthermore, the dropout and consequent echoes suggest that the radial migration of relativistic electrons is induced by the strong dusk-dawn asymmetric interplanetary shock compression on the magnetosphere.« less
  • To achieve a better understanding of the dominant loss mechanisms for the rapid dropouts of radiation belt electrons, three distinct radiation belt dropout events observed by Van Allen Probes are comprehensively investigated. For each event, observations of the pitch angle distribution of electron fluxes and electromagnetic ion cyclotron (EMIC) waves are analyzed to determine the effects of atmospheric precipitation loss due to pitch angle scattering induced by EMIC waves. Last closed drift shells (LCDS) and magnetopause standoff position are obtained to evaluate the effects of magnetopause shadowing loss. Evolution of electron phase space density (PSD) versus L* profiles and themore » μ and K (first and second adiabatic invariants) dependence of the electron PSD drops are calculated to further analyze the dominant loss mechanisms at different L*. Here, our findings suggest that these radiation belt dropouts can be classified into distinct classes in terms of dominant loss mechanisms: magnetopause shadowing dominant, EMIC wave scattering dominant, and combination of both mechanisms. Different from previous understanding, our results show that magnetopause shadowing can deplete electrons at L* < 4, while EMIC waves can efficiently scatter electrons at L* > 4. Compared to the magnetopause standoff position, it is more reliable to use LCDS to evaluate the impact of magnetopause shadowing. Finally, the evolution of electron PSD versus L* profile and the μ, K dependence of electron PSD drops can provide critical and credible clues regarding the mechanisms responsible for electron losses at different L* over the outer radiation belt.« less