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Observations and simulations of non-local acceleration of electrons in magnetotail magnetic reconnection events

Nature Physics volume 7, pages 360–365 (2011)Cite this article

Abstract

Magnetic reconnection in magnetized plasmas represents a change in magnetic field topology and is associated with a concomitant energization of charged particles that results from a conversion of magnetic energy into particle energy. In Earth’s magnetosphere this process is associated with the entry of the solar wind into the magnetosphere and with the initiation of auroral substorms. Using data from the THEMIS mission, together with global and test particle simulations, we demonstrate that electrons are energized in two distinct regions: a low-energy population (less than or equal to a few kiloelectronvolts) that arises in a diffusion region where particles are demagnetized and the magnetic topology changes, and a high-energy component (approaching 100 keV) that results from betatron acceleration within dipolarization fronts that sweep towards the inner magnetosphere far from the diffusion region. Thus, the observed particle energization is associated with both magnetic reconnection and with betatron acceleration associated with macroscopic flows.

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Figure 1: Observations from THEMIS P4 on 15 February 2008.
Figure 2: Bz component of the magnetic field and flows in the maximum pressure surface.
Figure 3: Simulated energy fluxes and observed energy fluxes from THEMIS P4 observations.
Figure 4: Plots of differential energy flux on the maximum pressure surface for two different energy channels.
Figure 5: Estimated change in the perpendicular energy flux from betatron acceleration in the simulation.

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Acknowledgements

We thank H. Kohne for help with programming and display of the data and simulation results. Research at UCLA was supported by NASA grant NNX08AO48G. We acknowledge NASA contract NAS5-02099 and V. Angelopoulos for use of data from the THEMIS Mission, specifically, C. W. Carlson and J. P. McFadden for the use of ESA data, D. Larson and R. P. Lin for the use of SST data, K. H. Glassmeier, U. Auster and W. Baumjohann for the use of FGM data, J. W. Bonnell and F. S. Mozer for the use of EFI data, and A. Roux and O. LeContel for the use of SCM data. K-J.H. and M.L.G. were supported, in part, by NASA’s Magnetospheric Multiscale and Cluster missions at the Goddard Space Flight Center. M.G.K. was supported, in part, by NASA Grant UCB NAS 5-02099. The computing was carried out on NASA’s Columbia Supercomputer.

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Authors and Affiliations

  1. Institute for Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California 90095-1567, USA

    Maha Ashour-Abdalla, Mostafa El-Alaoui, David Schriver, Robert Richard, Raymond Walker & Margaret G. Kivelson

  2. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, Code 673, USA

    Melvyn L. Goldstein & Kyoung-Joo Hwang

  3. Institute of Space Science and Technology, Nanchang University, 330031, China

    Meng Zhou

  4. Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA

    Margaret G. Kivelson

  5. University of Maryland, Baltimore County, Maryland 21250, USA

    Kyoung-Joo Hwang

Authors
  1. Maha Ashour-Abdalla
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Contributions

M.A-A. initiated the electron acceleration study using observations and simulations. She led the research project, participated in the analysis of all of the simulation and observation results. M.E-A. carried out the MHD simulations and identified the dipolarization fronts in the Global model. He also participated in the analysis. M.G. was the first to realize the importance of this study. From his experience of Cluster data, he realized the wide applicability of these results. M.Z. carried out the particle simulations and participated in the analysis of the particle results. D.S. participated in the analysis of the particle results. R.R. developed the algorithm for converting simulation counting rates into differential energy flux and carried out the betatron acceleration analysis. R.W. participated in the analysis of the simulation results with emphasis on the MHD results. M.G.K. helped with theoretical issues; in particular she suggested analysis to quantify the betatron acceleration. K-J.H. applied experience she gained from studying electron acceleration during other dipolarization events seen by Cluster.

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Correspondence to Maha Ashour-Abdalla.

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Ashour-Abdalla, M., El-Alaoui, M., Goldstein, M. et al. Observations and simulations of non-local acceleration of electrons in magnetotail magnetic reconnection events. Nature Phys 7, 360–365 (2011). https://doi.org/10.1038/nphys1903

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