Ion Signatures of Reconnection

Magnetic reconnection during periods of northward interplanetary magnetic field results in complex field line behavior. It has been shown that the velocity distribution of ions can be used as a diagnostic to determine the location of the reconnection site as well as the resulting field line topology. Ion observations in the high altitude (6-9Re) cusp region from Polar/TIDE reveal a mix of distinct ion populations (including cold ionospheric ions and magnetosheath ions) which can be attributed to different sources. In addition, the phase-space distributions of these ions reveal features which are attributed to reconnection and interactions with the magnetopause current layer (e.g. acceleration, counterstreaming, mixing of magnetosheath and ionospheric ions, and "D"-shaped distributions). These signatures has been used in several cases to infer the location of the reconnection site, the topology of the resulting field lines, and the location of the observation point relative to the magnetopause.