The existence and properties of the distant magnetotail during 32 hours of strongly northward interplanetary magnetic field

摘要

We report observations made by the Wind spacecraft in the distant magnetotail on 22–24 October 2003 when the interplanetary magnetic field (IMF) was strongly northward for more than 32 h. A well-defined magnetotail was observed down to at least X GSM = ?125 R E even after 32 h of strongly northward IMF conditions. However, the observed tail properties were strikingly different from the typical magnetotail. Although the closed field line plasma sheet was observed throughout the northward IMF interval, the usual mantle/lobe disappeared one hour after the northward IMF front reached the frontside magnetopause. Instead, open field lines were observed populated by field-aligned solar wind strahl electrons as well as plasma sheet electrons predominantly at 90° pitch angle. In essence, these observations provide evidence for reconnection between the IMF and a previously closed nightside cold dense plasma sheet during long periods of northward IMF, after poleward-of-the-cusp reconnection has depleted all open lobe field lines.