Counterstreaming electrons in magnetic clouds near 5 AU

Abstract

Suprathermal electron pitch angle spectrograms were searched for counterstreaming signatures in 31 magnetic clouds identified in Ulysses data when the spacecraft was located ∼5 AU from the Sun. Under the assumption that counterstreaming indicates closed field lines, that is, field lines attached to the Sun at both ends, we find that the clouds range from 0 to 100% closed, with an average of 55% closed, and that the percentage of closed flux tends to increase with increasing cloud size. The results are similar to those found at 1 AU, implying that the rate at which a cloud opens, presumably by interchange reconnection back at the Sun, slows significantly as its leading edge moves further out into the heliosphere. Copyright 2004 by the American Geophysical Union.