Generation of the fast solar wind: A review with emphasis on the resonant cyclotron interaction

[1] In situ measurements of the solar wind and remote observations of coronal holes have strongly implicated the resonant interaction with ion cyclotron waves as the responsible mechanism for heating and accelerating coronal hole ions to generate the fast solar wind. We review the current observational and theoretical knowledge of this mechanism and the progress that has been made in modeling the solar wind properties that result from this interaction. We begin by examining the observational and theoretical motivations for the continued study of this mechanism, including a brief historical review of these ideas. We then discuss the interplay of the resonance condition and the wave dispersion relation, which determines which ions can exchange energy with the waves. The physical basis for the interaction is then described, and we derive simple expressions for the ion response to the resonant wave dissipation. The complicated topic of oblique propagation is dealt with next, including how the resonant interaction operates for obliquely propagating waves. The plasma response to the resonant dissipation is often approximated by treating the ion populations as fluids, and we examine the solar wind models which incorporate various versions of this interaction. We then present a sample model that illustrates many of the properties and shortcomings of the current fluid results in this area. However, the resonant interaction is most accurately treated with a kinetic description of the ions and the recent attempts to construct kinetic models are explored. We close with a discussion of the many observational and theoretical gaps in our understanding that remain, including a presentation of alternative mechanisms and some speculations on future developments in this field.