Proton temperature anisotropy in the fast solar wind: Turbulence-driven dispersive ion cyclotron waves

The effects of parallel propagating ion cyclotron waves on the solar wind plasma are investigated in an attempt to reproduce the observed proton temperature anisotropy. The model calculations presented here assume that a nonlinear cascade process, at the Kolmogorov rate, transports energy from low-frequency Alfven waves to the ion cyclotron resonant range. The energy is then picked up by the plasma through the resonant cyclotron interaction. Ion cyclotron waves are found to play an important role in shaping the proton temperature anisotropy starting in the inner corona and extending to interplanetary space. Dispersive ion cyclotron waves are able to cool protons more significantly than nondispersive ones.