Convective amplification of drift-acoustic waves in sheared flows

Abstract

The evolution of wave packets is investigated in a cold-ion plasma model with sheared magnetic and velocity fields. Wave packets may be amplified by the drift Kelvin–Helmholtz mechanism even when the velocity shear is such that normal modes are stable. It is shown that the logarithm of the convective amplification can be an order of magnitude greater than the logarithm of the steady-state amplification often taken as the measure of convective instability. For a given wave number, the maximum of either of these amplifications decreases only as the inverse of the perpendicular component of the velocity shear.