Instability of inertial Alfvén waves in transverse sheared flow

Abstract

We study the stability of dispersive Alfvénic structures with transverse scales near the electron inertial length c/ωpe. As demonstrated by Seyler and Wu [2001], inertial Alfvén waves can be driven unstable by the parallel current sheets associated with the Alfvénic structures. In this paper we extend that study by including the effect of the transverse sheared flow due to the E × B drift. We show that the sheared flow decreases the growth rate of the instability, but the instability still exists even in the presence of the shear. In addition, we show that the sheared flow itself can drive the plasma unstable. Owing to a resonance between the sheared flow velocity and the phase velocity of the Alfvén wave, energy can be transferred from the sheared flow to the wave, driving the plasma unstable. We present an extensive analytical study of the linear stability. The result of this paper shows how inertial Alfvén waves can be generated in the auroral region and may explain the origin of broadband extremely low frequency (BBELF) waves associated with Alfvénic structures.