Properties of lower hybrid solitary structures: A comparison between space observations, a laboratory experiment, and the cold homogeneous plasma dispersion relation

Abstract

Lower hybrid solitary structures have been observed by sounding rockets in the auroral ionosphere for over a decade and a half. Surprisingly, few laboratory experiments have attempted to reproduce this interesting phenomena. Recently, Rosenberg and Gekelman [2001] investigated the interaction between fluctuations near the lower hybrid resonance and field‐aligned density striations using the Large Plasma Device at the University of California, Los Angeles. The laboratory measurements of electromagnetic fluctuations localized in a plasma density gradient are new and interesting. This experiment represents another in a series of laboratory investigations that use predictions of the cold homogeneous plasma dispersion to interpret observations of lower hybrid fluctuations interacting with a zero‐order plasma density gradient [Bamber et al., 1994, 1995; Rosenberg and Gekelman, 1998]. This experiment is also the first attempt to directly compare laboratory phase velocity estimates with interferometric electric field measurements of lower hybrid solitary structures by the AMICIST, TOPAZ III and PHAZE II sounding rockets [Pinçon et al., 1997; Schuck et al., 1998; Bonnell et al., 1998]. This paper compares the laboratory and space measurements and concludes that they represent completely different phenomena. Furthermore, significant discrepancies between the predictions of the cold homogeneous plasma dispersion relation and the laboratory observations are presented. We speculate that these discrepancies arise because plasma density gradients, essential to description of the laboratory experiment, are neglected in the cold homogeneous plasma dispersion relation.