Lower hybrid drift instability at a dipolarization front

Abstract

AbstractWe present observations of a reconnection jet front detected by the Cluster satellites in the magnetotail of Earth, which are commonly referred to as dipolarization fronts. We investigate in detail electric field structures observed at the front which have frequency in the lower hybrid range and amplitudes reaching 40 mV/m. We determine the frequency and phase velocity of these structures in the reference frame of the front and identify them as a manifestation of the lower hybrid drift instability (LHDI) excited at the sharp density gradient at the front. The LHDI is observed in the nonlinear stage of its evolution as the electrostatic potential of the structures is comparable to ∼ 10% of the electron temperature. The front appears to be a coherent structure on ion and MHD scales, suggesting existence of a dynamic equilibrium between excitation of the LHDI and recovery of the steep density gradient at the front.