Articles | Volume 33, issue 2
Regular paper
03 Feb 2015
Regular paper |  | 03 Feb 2015

Dual-spacecraft reconstruction of a three-dimensional magnetic flux rope at the Earth's magnetopause

H. Hasegawa, B. U. Ö. Sonnerup, S. Eriksson, T. K. M. Nakamura, and H. Kawano

Abstract. We present the first results of a data analysis method, developed by Sonnerup and Hasegawa (2011), for reconstructing three-dimensional (3-D), magnetohydrostatic structures from data taken as two closely spaced satellites traverse the structures. The method is applied to a magnetic flux transfer event (FTE), which was encountered on 27 June 2007 by at least three (TH-C, TH-D, and TH-E) of the five THEMIS probes near the subsolar magnetopause. The FTE was sandwiched between two oppositely directed reconnection jets under a southward interplanetary magnetic field condition, consistent with its generation by multiple X-line reconnection. The recovered 3-D field indicates that a magnetic flux rope with a diameter of ~ 3000 km was embedded in the magnetopause. The FTE flux rope had a significant 3-D structure, because the 3-D field reconstructed from the data from TH-C and TH-D (separated by ~ 390 km) better predicts magnetic field variations actually measured along the TH-E path than does the 2-D Grad–Shafranov reconstruction using the data from TH-C (which was closer to TH-E than TH-D and was at ~ 1250 km from TH-E). Such a 3-D nature suggests that the field lines reconnected at the two X-lines on both sides of the flux rope are entangled in a complicated way through their interaction with each other. The generation process of the observed 3-D flux rope is discussed on the basis of the reconstruction results and the pitch-angle distribution of electrons observed in and around the FTE.

Short summary
A novel data analysis technique for recovering three-dimensional (3-D) magnetic field structures from in situ measurements by two satellites is applied for the first time to a magnetic flux rope observed by the THEMIS spacecraft near the Earth's subsolar magnetopause. We found that the flux rope resulting from multiple X-line reconnection was significantly 3-D and consisted of the field lines with different topologies, suggesting a complex interaction of the solar wind and the magnetosphere.