Filamentary structures in the magnetotail lobes

Filamentary structures consisting of energetic plasma have been observed in the magnetotail lobes. Using plasma, energetic particle, composition, and magnetic field data from the ISEE 1 and 2 spacecraft, we have established that these structures may be related to polar cap auroras. The filaments consist of energetic (several keV) plasma with a quasi‐isotropic or field‐aligned velocity distribution similar to that in the plasma sheet boundary layer. Composition analysis reveals that the origin of the plasma is the plasma sheet or plasma sheet boundary layer. The gradients in the energetic particle fluxes show that the structures are approximately aligned in the XZ plane, so that the possibility of simple plasma sheet flapping can be ruled out. Field‐aligned currents are associated with the filamentary structures. The current densities when mapped along the magnetic field lines are comparable with low‐altitude measurements over the polar cap. While the occurrence of the filaments is not correlated with interplanetary conditions, the convection pattern within the filaments appears to be related to the interplanetary magnetic field direction. When the IMF B Z is positive, the E × B convection is in the sense of a dusk‐to‐dawn electric field. Our observations of field‐aligned currents and plasma convection are consistent with those made by polar‐orbiting satellites.