Plasmaspheric material on high-latitude open field lines

During periods of increased geomagnetic activity, cold and dense plasmasphe ric material is observed to drain from the inner magnetosphere toward the d ayside magnetopause. Geosynchronous observations have shown that plasmasphe ric material may participate in the dayside reconnection. However, predicti ons of plasmaspheric material passing through the polar region on recently opened field lines have not yet been confirmed by observations. We present evidence for the existence of such plasmaspheric material on high-latitude open magnetic field lines based on our investigations of 20 months of Inter ball/Hyperboloid observations and 11 months of Polar/Thermal Ion Dynamics E xperiment (TIDE) observations. In order to distinguish plasmaspheric materi al from the low-energy portion of entering magnetosheath plasma from the so lar wind, observed phase-space densities are compared to modeled magnetoshe ath and plasmaspheric phase-space densities. The phase-space density distri bution function of magnetosheath ions is estimated from upstream solar wind parameters using the gasdynamic theory. Twenty-one events were found in wh ich Interball passed through open field lines on the dayside during periods of increased geomagnetic activity, two of which show evidence for the pres ence of plasmaspheric material. Additionally, six such events were identifi ed from the Polar/TIDE database. Although the occurrence frequency is low, evidence of cold plasmaspheric material being transported on high-latitude open field lines does exist.