Articles | Volume 9, issue 2
Nonlin. Processes Geophys., 9, 75–78, 2002
https://doi.org/10.5194/npg-9-75-2002

Special issue: Theory and simulation of Solar System Plasmas, No. 3

Nonlin. Processes Geophys., 9, 75–78, 2002
https://doi.org/10.5194/npg-9-75-2002

  30 Apr 2002

30 Apr 2002

A universal mirror wave-mode threshold condition for non-thermal space plasma environments

M. P. Leubner and N. Schupfer M. P. Leubner and N. Schupfer
  • Institute for Theoretical Physics, University of Innsbruck, Austria

Abstract. Magnetic fluctuations are recognized in a large variety of space plasmas by increasingly high resolution, in situ observations as mirror wave mode structures. A typical requirement for the excitation of mirror modes is a dominant perpendicular pressure in a high-beta plasma environment. Contrary, we demonstrate from a realistic kinetic analysis how details of the velocity space distributions are of considerable significance for the instability threshold. Introducing the most common characteristics of observed ion and electron distributions by a mixed suprathermal-loss-cone, we derive a universal mirror instability criterion from an energy principle for collisionless plasmas. As a result, the transition from two temperature Maxwellians to realistic non-thermal features provides a strong source for the generation of mirror wave mode activity, reducing drastically the instability threshold. In particular, a number of space-related examples illuminate how the specific structure of the velocity space distribution dominates as a regulating excitation mechanism over the effects related to changes in the plasma parameters.