The excitation of lower hybrid waves driven by the ∇B effect in the current sheet

Abstract

We have investigated the excitation of electrostatic and electromagnetic lower hybrid waves in the magnetic field reversal region of the plasma sheet using a two‐fluid approach. We consider a two‐dimensional tail configuration that includes the Bx and Bz magnetic field components and examine the nonlocal properties of lower hybrid modes near the weak field region, where the field Bx(z) reverses sign. We have shown that an electrostatic lower hybrid mode is excited by the magnetic field gradient while electromagnetic modes are driven unstable by the combined effects of the magnetic field gradient and the electron fluid drift across the Bx field. We have shown that the electrostatic and electromagnetic lower hybrid modes grow in a few milliseconds and a few tens of milliseconds, respectively, the former for wavelengths shorter than the current sheet width (that is, for kyλ ≥ 1, where λ is the current sheet width) and the latter for long wavelengths (kyλ ≪ 1).