DYNAMICS OF THE SOLAR ATMOSPHERE .6. RESONANT OSCILLATIONS OF AN ATMOSPHERIC CAVITY - OBSERVATIONS

We have evaluated new, spatially one- and two-dimensional time series of photospheric and chromospheric Fraunhofer lines at a large number o f positions in the line profile, with the 'lambdameter' method. As a r esult we have obtained the velocity and brightness fluctuations corres ponding to many closely staggered height levels in the atmosphere, and their respective phase spectra as a diagnostic of the wave fields inv olved. This material has not only served to define more accurately and specifically the character of the 180 degrees phase jump observed bef ore in V-I spectra of the NaD2 line in internetwork regions, and to re veal the narrow height interval that gives rise to this discontinuity in the phase spectra. We have also discovered another discontinuity in V-V spectra of the same Fraunhofer line at nearly the same frequency (7.0 mHz). Since neither running nor standing waves alone can explain the observed solitary phase discontinuities, our results provide stron g evidence in favour of an atmosphere that supports (at least, and pro bably more than) one eigenmode as a component of the wave field.