Magneto-hydrodynamic shocks.

Abstract

This paper is a description of the alterations produced in, the physical properties of a magnetohydrodynamic fluid with infinite conductivity by the passage of a shock front. The two-dimensional case is considered, according to the equations of de Hoffman & Teller.' The shock is described in terms of three parameters measuring the shock strength, the relative importance of the magnetic field, and the obliqueness of the shock front. Expressions for various quantities of interest, such as the velocities and the ratio of the densities on either side of the shock front, are obtained. The essentially complicated nature of the problem is mauifested in an equation relating the relative importance of the magnetic field with the amount of bending the lines of force suffer upon passing through the shock front. A preliminary investigation of possible solutions of this equation indicates that very weak magnetic fields may be substantially amplified by the passage of such shock fronts. It is tentatively proposed, pending further numerical investigation of the solutions, that in a magneto-hydrodynamic fluid in which shock waves are not infrequent a possible mechanism may exist for the amplification of weak magnetic fields until the magnetic energy per unit volume obtained is within an order of magnitude or so of the pressure. I. Phys. Rev. 8o, 692, 1950. Yerkes Observatory, Williams Bay, Wis.