Global Oscillations of the Sun

Abstract

The topic of this Joint Discussion has received enormously increased interest in the last couple of years, owing to its potential for the investigation of the structure of the interior of the sun, including related topics like the structure of the convection zone, solar metal abundance, and the still unsettled neutrino problem.The first stimuli came from the startling observations of Hill et al. (1976) in Arizona, Severny et al. (1976) on Crimea, and Brookes et al. (1976) in Birmingham, accompanied by a large volume of theoretical papers, the details of analysis of which soon went beyond the actual status of the observational facts.We then witnessed, however, the success of considerable refinements of the techniques of observation, together with an obvious widespread temptation to push the interpretation of many of the new results to the limits of optimism. Yet, despite of the still increasing body of data suggesting the reality of the solar origin of the observed phenomena, much scepticism was prompted by the complicated statistics and the intricate numerical procedures involved in the data analysis, as well as by the great uncertainty about the significance and the amounts of “noise” contributed to the signal by electronics, changes of the conditions of the ray path within the telescope, terrestrial atmospheric inhomogeneities and solar quasi-stationary motions.

Variability in the power spectrum of solar five-minute oscillations

“…The fundamental, or Po, ridge possesses substantially less power than the other ridges, in keeping with previous observational results (e.g. Deubner et al, 1979;Rhodes et al, 1981). There is also considerable variation in power along any given ridge, with the power often appearing to be distributed in a succession of peaks and troughs.…”

“…In support of this conjecture, we note that our method of probing responds best to subphotospheric velocity and temperature structures which have a spatial scale that is a significant fraction of the ~ 700 Mm length of our observing window. There are ample theoretical reasons for expecting large-scale convection cells to be present that would possess such dimensions (e.g., Gilman, 1980;Toomre, 1980;Latour et aI. 1981Latour et aI.…”

“…Ridge structures are evident in spatial and temporal (k, co) power spectra of the observed five-minute oscillations of the Sun (e.g., Deubner et al, 1979). Such ridges in power arise because acoustic waves trapped in the thermal structure below the solar surface possess a fairly specific relationship between their frequency co and horizontal wavenumber k. Since the character of the oscillations is determined largely by the vertical stratification of temperature below the solar surface, the observed positions of the ridges could be compared with theory to determine at least the adiabat in the isentropic part of the convection zone (e.g., Berthomieu etal., 1980;Lubow etaL, 1980).…”