P. F. Moretti

Observational signatures of the interaction between acoustic waves and the solar magnetic canopy

Aims. We show that the spatial distribution (and its variation with frequency) of the power spectra of the velocity and intensity signals, in and around solar active regions, is a manifestation of the interaction of acoustic waves at the magnetic canopy. Methods. We analysed 6 h of simultaneous, full-disk, velocity and intensity images obtained using the MOTH instrument tuned in the Na D2 line at 589 nm and K D1 line at 770 nm, and full-disk velocity images from the SOHO/MDI experiment using the Ni line at 677 nm. Results. We propose that more than one type of magneto-acoustic-gravity wave is required to explain the well-known phenomena of p-mode absorption and power halos.

How Well Can We Infer the Properties of the Solar Acoustic Sources

Measurements of the p-mode line asymmetry in the solar oscillation velocity power spectrum have been used on several occasions to infer the properties of the acoustic sources. These inferences are based on the assumption that, unlike the observed intensity signal, the velocity signal does not contain a nonresonant (background) component that is correlated with the p-mode signal. Line asymmetry measurements have also been used to draw inferences on the nature of the correlated background signal that is present in intensity observations. By simultaneously modeling the observed velocity and intensity power spectra and the intensity-velocity cross spectrum, we enforce strict observational constraints on the properties of the fitting model. We find that in order to accurately describe the observed data, we have to include a correlated background component in both our models for the V and I signals at low frequencies. Our results also show that we cannot uniquely determine the acoustic source depth for low-frequency waves or the detailed properties of the correlated background signals. It appears that further physical and/or observational constraints are needed before we can obtain this information.