DISSIPATION OF PICKUP-INDUCED WAVES - A SOLAR-WIND TEMPERATURE INCREASE IN THE OUTER HELIOSPHERE

The deposition of energy into the solar wind by the pickup of interstellar neutrals is due to both the creation of hot, nonthermal ions and the associated generation of low frequency magnetohydrodynamic (MHD) waves. Dissipation of some fraction of the free wave energy released by ion pickup and isotropization is possible through nonlinear turbulent processes which may lead to heating of the core thermal solar wind proton distribution. Simple energy budget arguments are utilized to show that pickup ion generated wave dissipation may play a significant role in determining the solar wind radial temperature profile in the outer heliosphere. In particular, depending on the density of interstellar hydrogen in the heliosphere, there will be some radial distance beyond which the thermal solar wind core temperature increases steadily until the termination shock. Existing Pioneer and Voyager temperature profiles are consistent with this interpretation.