Polar cusp and vicinity under strongly northward interplanetary magnetic field on April 11, 1997: Observations and MHD simulations

We present a correlative case study of the solar wind interaction with the magnetosphere using in situ observations of the polar cusp and surrounding regions, ground-based and low-altitude spacecraft polar cap observations, and global MHD simulations during an extended period of strongly northward interplanetary magnetic field (IMF) on April 11, 1997. Within this extended period of strongly northward IMF, the Polar spacecraft entered a region with magnetosheath-like plasma and field lines above the polar cusp. Data from multiple instruments on Polar showed that the observed signatures can be interpreted as Polar entering the reconnection layer and crossing the current layer associated with it. The magnetosheath-like field lines encountered by Polar have just reconnected poleward of the polar cusp in the north. The reversed ionospheric convection patterns derived from the assimilative mapping of ionospheric electrodynamics (AMIE) technique show the reversed convection over the polar cap due to high-latitude reconnection throughout the whole interval. MHD simulations were performed using solar wind parameters observed by Wind, supporting the cusp reconnection interpretation.