HR: 1340h
AN: SM23A-1195    [Abstracts]
TI: Reconstruction of a bipolar magnetic signature in an earthward jet in the tail: Flux rope or 3D guide-field reconnection?
AU: * Hasegawa, H
EM: hase@stp.isas.jaxa.jp
AF: ISAS/JAXA, 3-1-1 Yoshinodai, Sagamihara, 229-8510, Japan
AU: Nakamura, R
EM: rumi@oeaw.ac.at
AF: Space Research Institute Austrian Academy of Sciences, Schmiedlstr. 6, Graz, A-8042, Austria
AU: Fujimoto, M
EM: fujimoto@stp.isas.jaxa.jp
AF: ISAS/JAXA, 3-1-1 Yoshinodai, Sagamihara, 229-8510, Japan
AU: Sergeev, V A
EM: victor@geo.phys.spbu.ru
AF: Institute of Physics, St. Petersburg State University, St. Petersburg, 198504, Russian Federation
AU: Lucek, E A
EM: e.lucek@imperial.ac.uk
AF: Blackett Laboratory Imperial College London, Prince Consort Road, London, SW7 2BW, United Kingdom
AU: Reme, H
EM: Henri.Reme@cesr.fr
AF: CESR, 9 Ave. du Colonel Roche, B.P. 4346, Toulouse, 31028, France
AU: Khotyaintsev, Y
EM: yuri@irfu.se
AF: Swedish Institute of Space Physics, Box 537, Uppsala, SE-75121, Sweden
AB: Southward-then-northward magnetic perturbations are often seen in the tail plasma sheet, along with earthward jets, but the generation mechanism of such bipolar Bz (magnetic flux rope created through multiple X-line reconnection, transient reconnection, or else) has been controversial. At ~23:13 UT on 13 August 2002, Cluster encountered a bipolar Bz at the leading edge of an earthward jet, with one of the four spacecraft in the middle of the current sheet. Application to this bipolar signature of Grad-Shafranov (GS) reconstruction, the technique for recovery of two-dimensional (2D) magnetohydrostatic structures, suggests that a flux rope with diameter of ~2 RE was embedded in the jet. To investigate the validity of the GS results, the technique is applied to synthetic data from a 3D MHD simulation, in which a bipolar Bz can be produced through localized (3D) reconnection in the presence of guide field By [Shirataka et al., JGR, 2006] without invoking multiple X-lines. A flux rope-type structure, which does not in fact exist in the simulation, is reconstructed but with a shape elongated in the jet direction. Unambiguous identification of a mechanism that leads to an observed bipolar Bz thus seems difficult based on the topological property in the GS maps. We however infer that a flux rope was responsible for the bipolar pulse in this particular Cluster event, because the recovered magnetic structure is roughly circular, suggesting a relaxed and minimum energy state. Our results also indicate that one has to be cautious about interpretation of some (e.g., force-free, or magnetohydrostatic) model-based results.
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2744 Magnetotail
DE: 2764 Plasma sheet
DE: 7833 Mathematical and numerical techniques (0500, 3200)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting