Do First Results from [ITAL]SOHO[/ITAL] UVCS Indicate that the Solar Wind is Accelerated by Solitary Waves?

Abstract

The Ultraviolet Coronagraph Spectrometer (UVCS) on board the recently launched US-European Solar and Heliospheric Observatory (SOHO) satellite has found O VI and H I emission lines with a broad component that corresponds to ~300 km s-1 unresolved motions at about 0.7 solar radii above the photosphere. These motions appear to be independent of ion mass. We suggest that the large Doppler broadening of the ion emission lines observed by the UVCS are signatures of solitary waves in the solar wind plasma. According to our recent 2.5-dimensional (i.e., three-dimensional with azimuthal symmetry) MHD simulations, these waves may contribute significantly to the solar wind acceleration and may generate velocity fluctuations with a magnitude that agrees with the above observations.