THE DETECTION OF WAVE ACTIVITY IN THE SOLAR CORONA USING UV LINE SPECTRA

The SUMER and CDS instruments on the Solar and Heliopheric Observatory spacecraft (SOHO), due to be launched in 1995, may enable us to identify the dominant mechanism responsible for solar coronal heating. In this paper we examine, in particular, the possibility that Alfve'n or acoustic waves, propagating through the corona and heating the ambient plasma, could be detected through the measurement of ultra-violet line widths. The contribution of wave broadening to the total line width depends on the orientation of the magnetic field with respect to the line of sight. CDS may be used to identify the magnetic field geometry in a particular region. The spatial resolution provided by SUMER, superior to that of previous instruments, should then make it possible to discriminate between different broadening mechanisms. In the case of lines produced by heavy ions in the low corona, we find that the line width produced by an Alfve'n wave flux sufficiently high to heat the active corona corresponds to a Doppler temperature of up to twenty times the kinetic temperature.