Counterstreaming electrons in magnetic clouds
S. Shodhan, N. U. Crooker, R. J. Fitzenreiter, D. E. Larson, R. P. Lepping, S. W. Kahler, and J. T. Gosling
Space Sciences Laboratory, University of California, Berkeley, CA 94720
Two widely used signatures of interplanetary coronal mass ejections are counterstreaming suprathermal electrons, signaling magnetic structures connected to the Sun at both ends, and magnetic clouds, characterized by large-scale field rotations, low temperature, and high field strength. In order to determine to what extent these signatures coincide, electron heat flux data were examined for 14 magnetic clouds detected by ISEE 3/IMP 8 near solar maximum and 34 clouds detected by Wind near solar minimum. The percentage of time during each cloud passage that counterstreaming electrons were detected varied widely, from 6 clouds with essentially no counterstreaming to 10 clouds with nearly 100% counterstreaming. All of the former but only half of the latter occurred near solar minimum, suggesting a possible solar cycle dependence on the degree of openness. Overall the results are consistent with the view that magnetic field lines within a magnetic cloud can form a large-scale, coherent structure, usually interpreted as a flux rope, but that reconnection in remote regions of the structure, presumably near the Sun, can alter its topology from closed to open. In this view, magnetic field lines in magnetic clouds are in various stages of becoming ambient, open field lines.
J. Geophys. Res., submitted, 1999