Spectroscopic Observation of Coronal Waves

Abstract

A time sequence over 80 min of coronal green-line spectra was obtained with a corona- graph at the Norikura Solar Observatory. Doppler velocities, line intensities, and line widths were derived through fitting a single Gaussian to the observed line profiles. Coronal waves have been clearly detected in the Doppler velocity data. The Fourier analysis shows powers in a 1–3 mHz range, and in higher frequencies (5–7 mHz) at localized regions. The propagation speed of the waves was estimated by correlation analysis. The line intensity and line width did not show clear oscillations, but their phase relationship with the Doppler velocity indicates propagating waves rather than standing waves. The existence of Alfvén waves whose speed is 500 km s–1 or faster is possible but inconclusive, while the existence of slower waves (of the order of 100 km s–1, possibly sound waves) is evident. The energy carried by the detected sound waves is far smaller than the required heat input rate to the quiet corona.