Alfvén waves in the solar corona and solar wind

Abstract

Alfvén waves have long been known to be a major component of the turbulence measured in situ in the interplanetary medium. Until recently, however, observations had been limited to the ecliptic plane, where the solar wind structure is complicated by the interaction of fast and slow solar wind streams, the Alfvénic turbulence being essentially limited to high-speed streams in well defined magnetic sectors. The Ulysses spacecraft has shown how this structure disappears with increasing latitude, leading to a relatively constant high-speed stream originating from polar coronal holes. Within this region the radial magnetic field appears to be relatively constant with latitude, and the fluctuations are everywhere dominated by large-amplitude Alfvén waves propagating away from the sun, covering a broad band of wavelengths. Here we discuss the origin and evolution of solar wind Alfvén waves; the possible role played by such fluctuations in the heating of the corona and acceleration of the high-speed wind is explored in the light of both analytical models and numerical simulations.