Heating and cooling of protons by turbulence-driven ion cyclotron waves inthe fast solar wind

The effects of parallel propagating nondispersive ion cyclotron waves on th e solar wind plasma are investigated in an attempt to reproduce the observe d proton temperature anisotropy, namely, T-p perpendicular to >> T-p parall el to in the inner corona and T-p perpendicular to < T-p parallel to at 1 A U. Low-frequency Alfven waves are assumed to carry most of the energy neede d to accelerate and heat the fast solar wind. The model calculations presen ted here assume that nonlinear cascade processes, at the Kolmogorov and Kra ichnan dissipation rates, transport energy from low-frequency Alfven waves to the ion cyclotron resonant range. The energy is then picked up by the pl asma through the resonant cyclotron interaction. While the resonant interac tion determines how the heat is distributed between the parallel and perpen dicular degrees of freedom, the level of turbulence determines the net diss ipation. Ion cyclotron waves are found to produce a significant temperature anisotropy starting in the inner corona, and to limit the growth of the te mperature anisotropy in interplanetary space. In addition, this mechanism h eats or cools protons in the direction parallel to the magnetic field. Whil e cooling in the parallel direction is dominant, heating in the parallel di rection occurs when T-p perpendicular to >> T-p parallel to. The waves prov ide the mechanism for the extraction of energy from the parallel direction to feed into the perpendicular direction. In our models, both Kolmogorov an d Kraichnan dissipation rates yield T-p perpendicular to >> T-p parallel to in the corona, in agreement with inferences from recent ultraviolet corona l measurements, and predict temperatures at 1 AU which match in situ observ ations. The models also reproduce the inferred rapid acceleration of the fa st solar wind in the inner corona and flow speeds and particle fluxes measu red at 1 AU. Since this mechanism does not provide direct energy to the ele ctrons, and the electron-proton coupling is not sufficient to heat the elec trons to temperatures at or above 10(6) K, this model yields electron tempe ratures which are much cooler than those currently inferred fram observatio ns.