The Origin of Large-Scale Magnetic Flux Dropouts

T. H. Zurbuchen, S. Hefto, L. A. Fisk, G. Gloeckler, N. A. Schwadron, C. W. Smith, N. F. Ness, R. M. Skoug, D. J. McComas, and L. F. Burlaga

Journal of Geophysical Research, submitted 2000.

Abstract:

Magnetic holes are sudden changes in the magnetic field intensity |B| from typical interplanetary values (about 10 nT) to less than 1 nT in a matter of seconds. The intensity then recovers seconds up to 30 minutes later. These |B| dropouts can be seen daily; less often observed, but even more dramatic, are magnetic field depletions that least for up to 1 hour. We use selected periods of magnetic flux drop-outs observed with various sensors of the Advanced Composition Explorer (ACE) with a unique combination of magnetic field, plasma and composition experiments to establish the origin of these peculiar objects. Based on this combination of plasma, field and composition data we conclude that these magnetic flux drop-outs very likely are born in the heliosphere and are not of direct solar origin. We also suggest a possible formation mechanism which is associated with magnetic reconnection close to the Sun.