 |
| Titel |
Electron Acceleration in the Earth's Magnetotail Using Multi-Scale Simulations |
| VerfasserIn |
Maha Ashour-Abdalla, Giovanni Lapenta, Mostafa El-Alaoui, Raymond Walker |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090347
|
| Publikation (Nr.) |
 EGU/EGU2014-4577.pdf |
|
|
|
|
|
| Zusammenfassung |
| Magnetic reconnection in magnetized plasma represents a change in the topology of magnetic
fields and is associated with a concomitant energization of charged particles that results from
a conversion of magnetic energy into particle energy.
Using data from the THEMIS and Cluster missions together with global and test particle
simulations, we demonstrate that during a substorm on February 15, 2008 electrons
are energized in two distinct regions: A low-energy population (up to a few keV)
appears to arise in the diffusion region where particles are demagnetized and the
magnetic topology changes. In addition a high-energy component that is energized by
betatron acceleration arises within dipolarization fronts as they sweep toward the inner
magnetosphere far from the diffusion region. This study concluded that particle energization
is not associated solely with the conversion of magnetic to kinetic energy but, at
least in the magnetosphere, also arises in conjunction with macroscopic flows. In a
second substorm study, on March 11, 2008 we found that the test particle results
compared favorably with observations only when we added a high-energy tail to
the distribution function near the reconnection site. This implies that acceleration
near the X-line was substantial and needs to be included. THEMIS and Cluster
observations indicate that plasma waves are associated with the dipolarization fronts
[1]. The test particle calculations are not self-consistent and do not include plasma
waves. Therefore, to fully understand the processes that lead to electron acceleration
throughout the near-Earth tail, we need to utilize a self-consistent kinetic approach that
includes waves and electron acceleration near the neutral line along with large-scale
dynamics.
We present results from a model which couples the large scale magnetospheric processes
and kinetic processes by developing a simulation approach in which a global MHD
simulation is coupled with a particle in cell simulation. In this approach we couple the UCLA
global MHD code [2] with the iPIC3D implicit particle in cell code [3]. We use a two
dimensional version of iPIC3D to investigate the multi-scale nature of the electron
energization during the February 15, 2008 substorm. In this multi-scale simulation the
electric and magnetic fields show the quadrupolar signature of Hall-MHD which is absent in
the resistive MHD simulation. Moreover the electrons move much faster than the ions
especially at the separatrices and the inflow boundary. We note that during this
event, just like in the case of the MHD, dipolarization fronts are formed mainly
earthward of the neutral line. Finally, we find that electrons are energized near
both the x-line and dipolarization fronts, but the energization is greater at the latter
location.
[1] Zhou, M., M. Ashour-Abdalla, X. Deng, D. Schriver, M. El-Alaoui, and Y.
Pang (2009), THEMIS observation of multiple dipolarization fronts and associated
wave characteristics in the near-Earth magnetotail, Geophys. Res. Lett., 36(20),
L20107.
[2] El-Alaoui, M. (2001), Current disruption during November 24, 1996, substorm, J.
Geophys. Res., 106(A4), 6229–6245.
[3] Markidis, S., G. Lapenta, and Rizwan-uddin (2010), Multi-scale simulations of
plasma with iPIC3D, Math. Comput. Simulation, 80(7), 1509–1519. |
|
|
|
|
|
|