Observations of the ion signatures of double merging and the formation of newly closed field lines

Abstract

Observations from the Thermal Ion Dynamics Experiment (TIDE) on the Polar spacecraft, taken during a period of northward interplanetary magnetic field (IMF) show magnetosheath ions within the magnetosphere with velocity distributions resulting from two widely separated (∼30 RE) merging sites along the same field lines. These results are consistent with the hypothesis that double merging can produce closed field lines populated by solar wind plasma under northward IMF. While the merging sites cannot be unambiguously located, the directions of the flowing magnetosheath populations and the convection of merged field lines are consistent with locations of two merging sites northward of the spacecraft and the analyses favor one site poleward of the northern cusp and a second site at lower latitudes equatorward of the northern cusp.