Waves and instabilities in the solar wind

We present a review of waves and instabilities in the solar wind, concentrating on those aspects that are likely to play important roles in influencing the dynamic and thermodynamic states of the general solar wind expansion. We consider in particular the roles played by various waves and instabilities in influencing the heating and expansion of the solar wind, the angular momentum of the solar wind, the solar wind thermal anisotropy, the heating and flow of alpha particles in the solar wind, the interstellar neutral particles that become ionized in the solar wind, and the ''fluidlike behavior'' of the solar wind. We include a brief review of the properties of the hydromagnetic wave modes, concentrating particularly on the Alfven mode, which has been observed to contribute significantly to the microscale fluctuations of the solar wind. But we also present a summary of observational evidence pertaining to the presence and action in the solar wind of waves and instabilities that are not among the hydromagnetic modes. (auth)