Solar wind magnetic holes: Signatures of slow-mode type MHD solitons?

Abstract

Magnetic holes in the solar wind, first described by Turner (1977) and, more recently, in a comprehensive study on the basis of Ulysses field and plasma observations, by Winterhalter et al. (1994), are commonly believed to result from the mirror mode instability. Their origin, however, is still under debate. This paper introduces an alternative mechanism into the discussion that is not related to the mirror mode. We suggest an explanation of magnetic holes in terms of MHD solitons of mixed slow-mode/intermediate mode type which propagate with small velocity at large angles to the magnetic field. These structures can evolve as stable flow features in the sense of inverse scattering theory, from certain initial conditions in the solar wind plasma, without the need for a temperature anisotropy.