On the interpretation of five-minute oscillations in solar spectrum line shifts

Abstract

It is argued that p modes in the Sun are excited on average to a surface amplitude which, except for modes of highest degree, is a function of frequency alone. This hypothesis appears to be consistent with almost all the observational data in the frequency range 2–4 mHz. The sharp-line component in the power spectra of whole-disc measurements first reported by Claverie et al. is due to a near coincidence of the eigenfrequencies of modes of low degree, the modes to which the whole-disc measurements are most sensitive. Previous similar observations by Fossat & Ricort, Grec & Fossat and Dittmer did not isolate the sharp-line component partly because the observing intervals were too short, though the amplitudes of the motion observed are consistent with the hypothesis stated above. The amplitudes of modes of higher degree, which are responsible for the five-minute oscillations reported originally by Leighton, Noyes & Simon, are also roughly in accord.