Abstract
Abstract. We recover two-dimensional (2-D) magnetic field and flow field configurations from three spacecraft encounters with a single large-scale reconnection exhaust structure in the solar wind, using a new reconstruction method (Sonnerup and Teh, 2008) based on the ideal single-fluid MHD equations in a steady-state, 2-D geometry. The reconstruction is performed in the rest frame of the X-line, where the flow into, and the plasma jetting within, the exhaust region are clearly visible. The event was first identified by Phan et al. (2006) in the ACE, Cluster, and Wind data sets; they argued that quasi-steady reconnection persisted for over 2 h at a long (390 RE) X-line. The reconnection exhaust is sandwiched between two discontinuities, both of which contain elements of intermediate- and slow-mode behavior; these elements are co-located rather than being spatially separated. These composite discontinuities do not satisfy the coplanarity condition or the standard MHD jump conditions. For all three spacecraft, the Walén regression line slope was positive (negative) for the leading (trailing) discontinuity. Our MHD reconstruction shows that: (1) the X-line orientation was close to the bisector of the overall magnetic shear angle and exhibited a slow rotating motion toward the Sun-Earth line; (2) the X-line moved earthward, dawnward, and southward; (3) the reconnection electric field was small (~0.02 mV/m on average) and gradually decreased from the first crossing (ACE) to the last (Wind). The magnetic field and flow field configurations recovered from ACE and Cluster are similar while those recovered from Wind also include a magnetic island and an associated vortex. Reconnection persisted for at least 2.4 h involving inflow into the exhaust region from its two sides. Time-dependence in the reconnection electric fields seen by ACE and Wind indicates local temporal variations in the field configuration. In addition to the reconstruction results, we provide a description and analysis of many details from the crossings by the spacecraft.
Highlights
Magnetic reconnection is an important and efficient process for converting magnetic field energy to plasma kinetic and thermal energy
The magnetic field topology is changed by breaking and reconnecting oppositely directed frozen-in field lines from different plasma regions and the plasma flow is accelerated to speeds comparable to the Alfven speed
The resulting global normal vector of the current sheet is n =[+0.745, +0.570, −0.347](GSE), chosen to point sunward. It forms an angle of only 3.6◦ with the normal estimated by Phan et al (2006) using minimum variance analysis of the magnetic field (MVAB) (Sonnerup and Cahill, 1967) from Wind
Summary
Magnetic reconnection is an important and efficient process for converting magnetic field energy to plasma kinetic and thermal energy. Magneto-hydrostatic Grad-Shafranov (GS) reconstruction was originally proposed by Sonnerup and Guo (1996) and further developed by Hau and Sonnerup (1999) and Hu and Sonnerup (2003) It is a method of solving the GS equation as a spatial initial-value problem to produce maps of 2D, time-independent field and plasma structures, from data taken by one or more spacecraft traversing the structures. We apply the method to an event, first identified by Phan et al (2006), that occurred in the solar wind on 2 February 2002 It was observed by widely separated spacecraft (ACE, Cluster, and Wind) in sequence, so as to establish its enormous size and long duration.
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