Cusp observations of high‐ and low‐latitude reconnection for northward interplanetary magnetic field

Abstract

Polar/Toroidal Imaging Mass Angle Spectrograph (TIMAS) observations in the cusp reveal evidence of both high‐ and low‐latitude reconnection during high solar wind dynamic pressure, northward interplanetary magnetic field (IMF) intervals. Under these restrictive conditions, the magnetic field observed by the Polar/Magnetic Fields Investigation in the northern cusp often rotates from lobe‐like orientations (BZ<0, Bx>0) to dayside magnetospheric‐like orientations (Bz>0, Bx<0). Proton distributions observed when the magnetic field has a magnetospheric‐like orientation are consistent with either reconnection poleward of the cusp at high‐latitudes or reconnection equatorward of the cusp at lower latitudes. Transitions from one type of proton distribution to another as the field rotates from lobe‐like to dayside magnetospheric‐like orientations indicate sunward (poleward) convection of the reconnected magnetic field for reconnection poleward (equatorward) of the cusp. A survey of 17 intervals of high solar wind dynamic pressure and northward IMF indicates that these two reconnection topologies occur with approximately equal probability and that reconnection equatorward of the cusp favors small angles between the magnetosheath and dayside magnetospheric magnetic fields.