Using energetic electrons to probe the topology of the October 18–20, 1995 magnetic cloud

Abstract

We present ∼0.1–10 2 keV electron observations from the 3-D Plasma and Energetic Particles experiment of a magnetic cloud which passed by the WIND spacecraft on October 18 – 20, 1995. Although the magnetic field exhibits the smooth, continuous rotation signature of a helical flux rope, the electron observations show numerous abrupt discontinuities in flux level and anisotropy within the cloud. In addition, five solar impulsive electron events, accompanied by solar type III radio bursts, were observed while the cloud was passing by the spacecraft. The electron/type III events showed that some of the cloud field lines were magnetically connected to solar active region 7912. Analysis of the velocity dispersion in the arrival times of the solar impulsive electrons provides the length of magnetic field lines. The field line length is found to be longest (∼4 AU) near the exterior with a minimum (∼1.5 AU) near the center of the cloud, consistent with a helical flux rope model. We interpret the discontinuities in electron fluxes as evidence of disconnection of magnetic field lines from the Sun.