Magnetic impulse event: A detailed case study of extended ground and space observations

Abstract

Analysis of conjugate data from extended magnetometer networks in northern and southern high latitudes is used to elucidate the initiation and the evolution of a magnetic impulse event (MIE) on June 6, 1997. In addition, data from all‐sky imagers, imaging riometers, and Super Dual Auroral Radar Network radars in Antarctica are investigated to confirm the energy content, motion, and electrical current structure of the MIE. The MIE was accompanied by traveling convection vortices (TCVs) that began at ∼10 MLT and moved eastward (toward dusk) and slightly equatorward at 1–3 km/s across the noon meridian with north‐south conjugacy. The MIE had upward field‐aligned currents with soft electron precipitation that was located near the trailing edge of the Hall current loop. During the MIE interval the interplanetary magnetic field (IMF) was directed strongly outward from the Sun (Bx = −5 nT), with a slightly positive (1–2 nT) Bz, and a nearly zero By. Since abrupt solar wind pressure changes are unlikely under this IMF orientation (and none was, in fact, observed), classical mechanisms for MIE generation, such as a pressure pulse or dayside reconnection, are excluded. It is speculated that an abrupt IMF cone angle change from 60° to 20°, ∼30 min prior to the MIE onset, may have been an indirect trigger of this event via the interaction between the solar wind and the bow shock.