Observation of a retreating x line and magnetic islands poleward of the cusp during northward interplanetary magnetic field conditions

Autor: Frederick Wilder, Paul Cassak, Stephen A. Fuselier, Bjørn Lybekk, K. J. Trattner, Stefan Eriksson
Rok vydání: 2014
Předmět:
Zdroj: Journal of Geophysical Research: Space Physics. 119:9643-9657
ISSN: 2169-9402
2169-9380
Popis: When the interplanetary magnetic field is northward, reconnection occurs in each hemisphere on lobe field lines, poleward of the cusp. We have identified a case where the Cluster spacecraft crossed the magnetopause and encountered a tailward retreating x line. The x line is identified by the encounter of both a tailward and sunward jet, as well as Hall magnetic field signatures in the out-of-plane direction. Additionally, we find no signatures of electron heating and hypothesize that the spacecraft is too close to the x line to observe the accelerated electrons. Using two spacecraft, we are able to resolve the velocity of the structure, which moves near the magnetosheath speed. The speed of the x line is also consistent with the asymmetric reconnection theory. To our knowledge, this is the first time the speed of a retreating x line has been measured directly. Additionally, we observe ion distribution functions with counterstreaming populations, suggesting that a second x line formed sunward of the original one, leading to a magnetic island.
Databáze: OpenAIRE
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