ACOUSTIC-WAVE PROPAGATION IN THE SOLAR ATMOSPHERE .2. NONLINEAR RESPONSE TO ADIABATIC WAVE EXCITATION

We study the response of the solar atmosphere to excitations with adia batic large amplitude acoustic waves. Both monochromatic waves and aco ustic spectra are considered. For monochromatic excitation a critical frequency nu(cr) is found which separates different domains of resonan ce behaviour. Upon excitation with frequencies nu < nu(cr) the atmosph eric resonance decays rapidly with time as in the small amplitude wave case, while for nu > nu(cr), persistent resonance oscillations occur which are caused by shock overtakings. Excitation by acoustic spectra always leads to the nu > nu(cr) behaviour. Independent of the spectral shape and energy, acoustic spectra generate oscillations mainly at fr equencies nu = 6 - 7 mHz at the top of the chromosphere. The photosphe ric 5-min oscillation does not influence our chromospheric results. Sh ock heating by acoustic spectra is roughly similar to that of a monoch romatic wave of period 35 s. Irrespective of the initial spectral shap e and energy and even of the gravity and effective temperature of the star, a universal average shock strength M(S) = 1.5 is found. Due to o ur adiabatic treatment, the atmospheric slabs suffer extension which g rows with wave energy.