Two-spacecraft reconstruction of a magnetic cloud and comparison to its solar source

Abstract. This paper compares properties of the source region with those inferred from satellite observations near Earth of the magnetic cloud which reached 1 AU on 20 November 2003. We use observations from space missions SOHO and TRACE together with ground-based data to study the magnetic structure of the active region NOAA 10501 containing a highly curved filament, and determine the reconnection rates and fluxes in an M4 flare on 18 November 2003 which is associated with a fast halo CME. This event has been linked before to the magnetic cloud on 20 November 2003. We model the near-Earth observations with the Grad-Shafranov reconstruction technique using a novel approach in which we optimize the results with two-spacecraft measurements of the solar wind plasma and magnetic field made by ACE and WIND. The two probes were separated by hundreds of Earth radii. They pass through the axis of the cloud which is inclined −50 degree to the ecliptic. The magnetic cloud orientation at 1 AU is consistent with an encounter with the heliospheric current sheet. We estimate that 50% of its poloidal flux has been lost through reconnection in interplanetary space. By comparing the flare ribbon flux with the original cloud fluxes we infer a flux rope formation during the eruption, though uncertainties are still significant. The multi-spacecraft Grad-Shafranov method opens new vistas in probing of the spatial structure of magnetic clouds in STEREO-WIND/ACE coordinated studies.