Petschek‐type magnetic reconnection exhausts in the solar wind well inside 1 AU: Helios

Abstract

Petschek‐type reconnection exhausts can be recognized in solar wind plasma and magnetic field data as accelerated or decelerated plasma flows confined to magnetic field reversal regions. Using that characteristic signature, we have identified 28 reconnection exhausts in the Helios 1 and 2 data, thus extending observations of exhausts associated with local, quasi‐stationary reconnection in the solar wind inward to heliocentric distances of 0.31 AU. Most of the exhaust jets identified in the Helios data had the same general physical character as solar wind exhausts observed at greater heliocentric distances and latitudes by ACE, Wind, and Ulysses. The magnitude of the velocity changes from outside to inside the exhausts was generally comparable to, but somewhat less than (by a factor of 0.75 on average), the inflow Alfvén speeds. In a few of the Helios events, plasma number densities within the exhausts were intermediate to densities observed immediately outside, indicating that transitions from outside to inside the exhausts were not always slow‐mode‐like on both sides. We have identified pairs of closely spaced, but independent, reconnection exhausts bounding regions where the heliospheric magnetic field folded back toward the Sun. We find that plasma and magnetic field conditions in the high‐speed wind from coronal holes are not generally favorable for sustained magnetic reconnection and for the formation and propagation of Petschek‐type exhausts. Finally, we have not yet identified reconnection events common to both spacecraft, partially because of a relative lack of times when high data rate observations were available from both spacecraft.