Ionosphere and Ground-Based Response to Field-Aligned Current in the Magnetospheric Cusp Region

A special campaign was conducted at the Sondre Stromfjord incoherent scatter radar facility in October 1985 to study hydromagnetic and atmospheric gravity wave phenomena in the cusp region of the magnetosphere. During a day when the convection reversal boundary was measured just to the north of the radar, a field-aligned current filament of inferred amplitude is equivalent to 2x105 amps was measured at the boundary. Both ion and electron heating appeared to accompany the current filament. The convection velocity of the filament was found to be equivalent to 5 km/sec. Magnetic field data acquired in the southern conjugate hemisphere are used to conclude that the current filament occurred on closed field lines and, as such, was probably not indicative of a flux transfer event. The current filament may be evidence of the magnetosphere boundary layer on closed field lines, perhaps produced by the injection of magnetosheath plasmoids onto the field lines.