The Solar Source of the October 18-20, 1995 Magnetic Cloud inferred from WIND Electron Observations at 1 AU
While the WIND spacecraft at 1 AU was inside the magnetic cloud of October 18-20, 1995, five solar impulsive ~ 1-10(2) keV electron events were observed by the 3-D Plasma and Energetic particles experiment. The solar type III radio bursts produced by these electrons can be directly traced from ~ 1 AU back to x-ray flares at the Sun, providing the first direct identification of the footpoints of the cloud magnetic fields. One leg of this cloud clearly connects to a solar active region, AR 7912. The total magnetic flux within the cloud is estimated to be 10(13) Webers, implying that about 25% of the active region magnetic flux ( 4 x 10(13) Webers) is ejected in the cloud. Analysis of the arrival times of the electrons show that the lengths of the magnetic field lines in that leg vary from ~ 4 AU near the cloud exterior to ~ 1.5 AU near the cloud center, consistent with a force-free helical flux rope with ~ 8 turns total on the outside. The length of smooth Archimedean spiral ( ~ 1.15 AU) predicted for the observed solar wind speed of ~ 420 km/s, suggesting that the cloud may have expanded sideways (non-radially). Both the ~ 0.1 - 1 keV solar wind heat flux electrons and ~ 1-10(2) keV energetic electrons show numerous simultaneous abrupt changes in flux level and anisotropy, from bidirectional streaming to unidirectional streaming to complete dropouts within the cloud. We interpret these as evidence for patchy disconnection of one end or both ends of cloud magnetic field lines from the Sun, most likely due to magnetic reconnection occurring after the cloud was ejected.
AAS/Solar Physics Division Meeting #28
- Pub Date:
- May 1997