Properties of Open Fields in Magnetic Clouds at 1 AU and Implications for Patterns of Interchange Reconnection at the Sun

Most magnetic clouds encountered by spacecraft at 1 AU display a mix of unidirectional suprathermal electrons signaling open field lines and counterstreaming electrons signaling closed field lines (connected to the Sun at both ends). Assuming the open fields were originally closed loops that underwent interchange reconnection with open fields back at the Sun, we test for two properties of the open fields in clouds identified by the Wind spacecraft in order to gain information about the interchange reconnection process. The first test is for true polarity, determined from the direction of the suprathermal electrons relative to the magnetic field direction. Preliminary results indicate that the polarity of all open field lines within a given cloud is nearly always the same. This implies that interchange reconnection back at the Sun occurred systematically in only one leg of the flux rope loop as opposed to intermittently in both legs. This systematic interchange reconnection may play a role in the global circulation of open fields that reverses the polarity of the heliospheric field through the course of the solar cycle. The second test is for field inversion, determined from the direction of the true polarity relative to the local field direction. If the open fields are an integral part of the coils of a flux rope, as expected, then the spacecraft is as likely as not to intercept inverted fields, that is, fields locally turned back toward the Sun. Preliminary results indicate this to be true, with the caveat that often the fields point neither toward nor away from the Sun along the Parker spiral but rather orthogonal to it, as might be expected for flux ropes with axes tilted with respect to the ecliptic plane. These findings support the view that the large-scale field inversions identified earlier on open field lines at sector boundaries are quiet forms of loops or coils opened by interchange reconnection.