Suprathermal Populations and Their Effects in Space Plasmas: Kappa vs. Maxwellian

Abstract

Understanding the origin and implications of the suprathermal particle populations present in space plasmas is facilitated by the observations and theoretical interpretations using Kappa distribution models. Characteristic to collision-poor plasmas, such as the solar wind and planetary environments, suprathermal populations may significantly contribute to the energy budget of electrons and ions, with consequences on their temperature, bulk velocities, and the heat flux. Moreover, if present at low altitudes in the solar atmosphere, suprathermal particles can trigger the process of velocity filtration to explain coronal overheating, while the exospheric solar wind models of Kappa distributed populations are also able to predict the acceleration of fast streams (even originating in coronal holes). The present chapter reviews these concepts and physical properties on the basis of recent interpretations using comparisons between models based on Maxwellian and on Kappa distributions which bring improved and realistic perceptions of suprathermal plasma particles.