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| Titel |
A route to explosive large-scale magnetic reconnection in a super-ion-scale current sheet |
| VerfasserIn |
K. G. Tanaka, K. Haijima, M. Fujimoto, I. Shinohara |
| 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 ; 27, no. 1 ; Nr. 27, no. 1 (2009-01-23), S.395-405 |
| Datensatznummer |
250016380
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| Publikation (Nr.) |
 copernicus.org/angeo-27-395-2009.pdf |
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| Zusammenfassung |
| How to trigger magnetic reconnection is one of the most
interesting and important problems in space plasma physics. Recently,
electron temperature anisotropy (αeo=Te⊥/Te||) at the center of a current sheet and non-local effect of the
lower-hybrid drift instability (LHDI) that develops at the current sheet
edges have attracted attention in this context. In addition to these
effects, here we also study the effects of ion temperature anisotropy
(αio=Ti⊥/Ti||). Electron anisotropy
effects are known to be helpless in a current sheet whose thickness is of
ion-scale. In this range of current sheet thickness, the LHDI effects are
shown to weaken substantially with a small increase in thickness and the
obtained saturation level is too low for a large-scale reconnection to be
achieved. Then we investigate whether introduction of electron and ion
temperature anisotropies in the initial stage would couple with the LHDI
effects to revive quick triggering of large-scale reconnection in a
super-ion-scale current sheet. The results are as follows. (1) The initial
electron temperature anisotropy is consumed very quickly when a number of
minuscule magnetic islands (each lateral length is 1.5~3 times the
ion inertial length) form. These minuscule islands do not coalesce into a
large-scale island to enable large-scale reconnection. (2) The subsequent
LHDI effects disturb the current sheet filled with the small islands. This
makes the triggering time scale to be accelerated substantially but does not
enhance the saturation level of reconnected flux. (3) When the ion
temperature anisotropy is added, it survives through the small island
formation stage and makes even quicker triggering to happen when the LHDI
effects set-in. Furthermore the saturation level is seen to be elevated by a
factor of ~2 and large-scale reconnection is achieved only in this
case. Comparison with two-dimensional simulations that exclude the LHDI
effects confirms that the saturation level enhancement is due to the ion
anisotropy effects, while the LHDI effects shorten the overall time scale
significantly. The results imply that the ion temperature anisotropy is one
of the key properties that enable large-scale magnetic reconnection to
develop in a super-ion-scale current sheet. |
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