ON THE WEAKLY NONLINEAR KELVIN-HELMHOLTZ INSTABILITY OF TANGENTIAL DISCONTINUITIES IN MHD.

We derive a quadratically nonlinear equation that describes the motion of a tangential discontinuity in incompressible magnetohydrodynamics near the onset of a Kelvin-Helmholtz instability. We show that nonlinear effects enhance the instability and give a criterion for it to occur in terms of a longitudinal strain of the fluid motion along the discontinuity. [ABSTRACT FROM AUTHOR]