Cylindrical lower-hybrid electron holes at the Earth's dayside magnetopause

摘要

The analytic model of lower-hybrid electron holes (Jovanovi? and Shukla, 2004) is applied to analyze the strong coherent unipolar electric field signals perpendicular to the ambient magnetic field with a characteristic frequency in the lower-hybrid frequency range, recorded at the dayside magnetopause by the Polar mission (Mozer et al., 2004). On the basis of a good agreement with theoretical predictions, these structures are identified as the oblique cylindrical electron holes. Their localization results from the balance of nonlinearity associated with the electrons that are trapped along the magnetic field direction and undergo the × drift in the perpendicular direction and the dispersion provided by the electron polarization drift. It is suggested that electron holes can be related to the nonlinear evolution of the Buneman instability of lower-hybrid waves, driven by the parallel electric field that develops in the course of collisionless reconnection.