Spiky electric fields in the magnetotail

Large‐amplitude spiky electric fields which have been proposed to provide energization and heating of particles have been observed in many regions of the magnetosphere, including the bow shock, auroral zone, and plasma sheet boundary. We extend previous statistical studies of such fields in the magnetotail (which were limited to ≲ 22 R E ) to cover the region explored by the Geotail satellite. Results are presented concerning the occurrence frequency, location, and association with density gradients of spiky electric fields in the magnetotail at radial distances of ∼ 10–200 R E . Spiky fields do not occur beyond ∼ 100 R E , and they predominantly occur at or near the plasma sheet boundary (as indicated by changes in the spacecraft potential) and are always associated with waves near the lower hybrid frequency. Spiky fields occur preferentially during periods of higher magnetic activity ( Kp > 3). Statistical analysis of the direction of the largest field amplitudes provides information on the polarization of the waves and the spikes and therefore provides constraints on the origin of the fields. Waves which accompany the spikes are primarily polarized perpendicular to the magnetic field and are consistent with lower hybrid waves, while the spikes are polarized obliquely to the magnetic field. The results are described and compared with various possible generation mechanisms, including lower hybrid wave collapse, a leading candidate for explaining these spikes.