Overlapping ion populations in the cusp: polar/TIMAS results

The 90 degree inclined orbit of the Polar satellite crosses the cusp at intermediate altitudes (4 R E –6 R E ). The Toroidal Imaging Mass‐Angle Spectrograph (TIMAS) on the Polar spacecraft can obtain full energy/pitch angle distributions for four masses simultaneously. Many examples of magnetosheath particle injections with velocity dispersion, sometimes overlapping, have been observed. We report on two crossings of the cusp where TIMAS observed several overlapping cusp ion injections. These injections showed simultaneous onset of cusp ion precipitation at two different energies as well as the brief occurrence of ion precipitation above and below the energy of a preexisting population. Existing models of cusp precipitation do not provide an adequate explanation of these observations.