Energetic Electron Probes of Magnetic Cloud Topology

Magnetic clouds (MCs) are large interplanetary coronal mass ejections (ICMEs) of enhanced fields with rotations indicative of magnetic flux ropes originally connected to the Sun. The MC models require field lines with larger pitch angles and longer lengths with increasing distance from the MC axis. While the models can provide good fits to the observations, the global magnetic field geometry has not been tested, particularly for the field-line lengths. Impulsive solar energetic (E > 30 keV) electron events occurring within MCs can be used to infer the propagation distance and magnetic field-line length from the Sun at the point in the MC where the electron onset occurs. We surveyed the 18 MCs listed on the Wind/MFI MC list in or near which solar electron events were observed by the SSL/Berkeley 3DP instrument on the Wind spacecraft. By plotting the electron onset times as functions of their speeds for each event and taking their solar injections to coincide with observed type III radio bursts in the Wind/WAVES detector, the travel distances of the electrons along the field lines of the MCs were computed. Those electron travel distances were compared with the field-line lengths computed from two different MC model fits to test the models.