Heating of the solar wind in the outer heliosphere

Abstract

Small-scale Alfvturbulence in the outer helio- sphere is mainly determined by a source which is connected with the instability of the initially highly anisotropic velocity distribution of interstellar pick-up protons. The main portion of the generated turbulent energy is subsequently absorbed by the pick-up protons themselves due to the cyclotron- resonant interaction between waves and particles. A small fraction of this energy can be transferred to solar wind pro- tons resulting in their heating. The heating is more efficient in the high-speed solar wind.