Physics of Lower Hybrid Drift Waves and Anomalous Resistivity

Lower hybrid drift waves (LHDW) are frequently observed in the diffusion regions of magnetic reconnection. When there is enough free energy source, LHDW can be either quasi-electrostatic (ES-LHDW) or electromagnetic (EM-LHDW), depending on the plasma and field conditions. With a local, linear model [1,2], characteristics of LHDW and the transition from ES-LHDW to EM-LHDW are studied. Unlike the classical theory of ES-LHDW with kρ_e~1.2, our model shows that ES-LHDW has kρ_e~0.7. The difference is caused by the use of the Faraday induction equation rather than Poisson’s equation. When electromagnetic effects are included, the wavelength is expected to be larger. This difference is supported by space observations [1]. We also find that both electron beta and normalized drift velocity are important to determine whether LHDW is quasi-electrostatic or electromagnetic. Finally, we explain why ES-LHDW is capable of generating anomalous resistivity with an example observed in the Magnetic Reconnection Experiment (MRX). The fundamental reason is closely related to the free energy source of LHDW, the perpendicular current or relative drift between ions and electrons due to reconnecting current.