Solitary kinetic Alfvacute en waves on the ion-acoustic velocity branch in a low-β plasma

Starting with an exact nonlinear equation governing solitary kinetic Alfvacute en waves (SKAWs), a new type of SKAW on the ion-acoustic velocity branch is obtained in a low-β plasma. It propagates in a direction oblique to the ambient magnetic field, has a dispersion originating from the finite perpendicular wavelength, and is accompanied by a density hump soliton similar to that of the SKAWs on the Alfvacute en velocity branch in the case of 1>β>me/mi. It has a perturbed electric field with the same order as that of the latter SKAWs, but its perturbed magnetic field is weaker by a factor of (β/2)1/2, and in the small amplitude limit, the analytical result also leads to the Korteweg endash de Vries soliton. copyright 1996 American Institute of Physics