Grad‐Shafranov reconstruction with field‐aligned flow: First results

Abstract

Grad‐Shafranov (GS) reconstruction is a novel tool for recovering steady two‐dimensional (2‐D) coherent magnetic field structures from data taken by a single spacecraft. We present first results from a recently developed version of GS reconstruction that incorporates the effects of dynamically significant field‐aligned plasma flow. A new GS solver for this case has been developed and is benchmarked with an exact analytical solution. It is then applied to a magnetopause encounter by Cluster 1 (C1) and Cluster 3 (C3) on July 5, 2001. In the C1 crossing, a field‐aligned plasma flow, in the frame co‐moving with the local magnetopause structures, is present at approximately 57% of the Alfvén speed; in the C3 event the local flow is nearly Alfvénic. We find the following: (1) The recovered field maps are qualitatively similar to those obtained from magneto‐hydrostatic GS reconstruction, indicating that the latter can be fairly robust. (2) Our code provides new information about plasma structure and supersonic field‐aligned flow effects during reconnection. (3) We confirm results from the previous GS studies of the event, which indicated that significant time evolution occurred in the 30 s time lapse between the two crossings, owing to developing reconnection at a site close to the spacecraft. We provide an estimate of 0.47 mV/m for the reconnection electric field.