Z.E.Musielak, J.Staiger, M.Roth

Direct evidence for the existence of an acoustic cuto frequency in the solar atmosphere is given by observations performed by using the HELioseismological Large Regions Interferometric DEvice operating on the Vacuum Tower Telescope located on Tenerife. The observational results demonstrate variations of the cuto  with atmospheric heights. The observed variations of the cuto are compared to theoretical predictions made by using ve acoustic cuto frequencies that have been commonly used in helioseismology and asteroseismology. The comparison shows that none of the theoretical predictions is fully consistent with the observational data. The implication of this nding is far reaching as it urgently requires either major revisions of the existing methods of nding acoustic cuto frequencies or developing new methods that would account much better account for the physical picture underlying the concept of cuto frequencies in inhomogeneous media.

K.Murawski, P.Konkol, Z.E.Musielak

Recently Wiśniewska et al. demonstrated observationally how the acoustic cutoff frequency varies with height in the solar atmosphere including the upper photosphere and the lower and middle chromosphere, and showed that the observational results cannot be accounted for by the existing theoretical formulas for the acoustic cutoff. In order to reproduce the observed variation of the cutoff with atmospheric height, numerical simulations of impulsively generated acoustic waves in the solar atmosphere are performed, and the spectral analysis of temporal wave profiles is used to compute numerically changes of the acoustic cutoff with height. Comparison of the numerical results with the observational data shows good agreement, which clearly indicates that the obtained results may be used to determine the structure of the background solar atmosphere.