Observational Study of the Five-Minute Oscillations in the Solar Atmosphere. II: Coherence and Phase Spectra of Velocity and Intensity Fluctuations

Abstract

The coherence and phase spectra between velocity oscillations in different pairs of lines have been studied. The oscillation in the high level lines are found to lag behind those in the low level lines in general. There is high coherence between oscillations at the different levels. The phase differences between the velocities have insignificant values in the resonance range. This is taken to mean that they are standing waves. In the high-frequency range the phase difference observed is appropriate for the propagation of sound waves. The coherence and phase spectra of (i) the continuum brightness with the line wing and core brightness of Fe i 6358.695, and (ii) the continuum, line wing and core brightness of Fe i 6358.695 with the velocity fluctuations in the same line, have been studied. The core brightness leads the continuum by 57° in the resonance range. The intensity oscillations in the line core lead the velocity oscillations by 93°.5. This is taken as an additional evidence for the existence of standing waves.