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

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 mag- netic 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 em- bedded in the magnetopause. The FTE flux rope had a signif- icant 3-D structure, because the 3-D field reconstructed from the data from TH-C and TH-D (separated by 390 km) bet- ter predicts magnetic field variations actually measured along the TH-E path than does the 2-D Grad-Shafranov reconstruc- tion 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 com- plicated 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.