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| Titel |
Effects on magnetic reconnection of a density asymmetry across the current sheet |
| VerfasserIn |
K. G. Tanaka, A. Retinò, Y. Asano, M. Fujimoto, I. Shinohara, A. Vaivads, Y. Khotyaintsev, M. André, M. B. Bavassano-Cattaneo, S. C. Buchert, C. J. Owen |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 26, no. 8 ; Nr. 26, no. 8 (2008-08-15), S.2471-2483 |
| Datensatznummer |
250016204
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| Publikation (Nr.) |
 copernicus.org/angeo-26-2471-2008.pdf |
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| Zusammenfassung |
| The magnetopause (MP) reconnection is characterized by a
density asymmetry across the current sheet. The asymmetry is expected to
produce characteristic features in the reconnection layer. Here we present a
comparison between the Cluster MP crossing reported by Retinò et al. (2006) and virtual
observations in two-dimensional particle-in-cell simulation results. The
simulation, which includes the density asymmetry but has zero guide field in
the initial condition, has reproduced well the observed features as follows:
(1) The prominent density dip region is detected at the separatrix region
(SR) on the magnetospheric (MSP) side of the MP. (2) The intense electric
field normal to the MP is pointing to the center of the MP at the location
where the density dip is detected. (3) The ion bulk outflow due to the
magnetic reconnection is seen to be biased towards the MSP side. (4) The
out-of-plane magnetic field (the Hall magnetic field) has bipolar rather
than quadrupolar structure, the latter of which is seen for a density
symmetric case. The simulation also showed rich electron dynamics (formation
of field-aligned beams) in the proximity of the separatrices, which was not
fully resolved in the observations. Stepping beyond the
simulation-observation comparison, we have also analyzed the electron
acceleration and the field line structure in the simulation results. It is
found that the bipolar Hall magnetic field structure is produced by the
substantial drift of the reconnected field lines at the MSP SR due to the
enhanced normal electric field. The field-aligned electrons at the same MSP
SR are identified as the gun smokes of the electron acceleration in the
close proximity of the X-line. We have also analyzed the X-line structure
obtained in the simulation to find that the density asymmetry leads to a
steep density gradient in the in-flow region, which may lead to a
non-stationary behavior of the X-line when three-dimensional freedom is
taken into account. |
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