Propagation of Waves in the Solar Atmosphere.

The frequencies and horizontal wavenumbers at which the normal modes (large amplitude quasi-standing waves) of the solar atmosphere occur were calcu- lated for a semi empirical model of the region around the temperature minimum. At high frequencies the waves are compressional, modified by gravity, and can propagate into the upper atmosphere; at low frequencies the waves are gravitational, modified by compressibility, and can also propagate into the upper atmosphere. Between these two passhands is a trap baud where the waves are completely reflected. Three types of fundamental modes were found. The fundamental acoustic mode has ~~8x 10~ ku sec-1 for horizontal wavelengths smaller than 1000 km and goes to a constant frequency with a width 0.05> >0.032 sec-' for horizontal wavelengths greater than 2000 km. The fundamental acoustic-gravity mode be- haves like an acoustic mode for horizontal wavelengths greater than 6000 km, where it is composed of many narrow resonances of nearly constant frequency in the range 0.032>~~>0.009 sec-1. At smaller horizontal wavelengths it narrows and changes its behavior to that of a gravity mode with a frequency c~~0.03 sec-1. The fundamental gravity mode has o~~7.5 x 10 k11 sec-' at horizontal wavelengths greater than 3000 km and approaches a constant frequency ~~0.028 sec-' at small horizontal wavelengths. The calculated fundamental acoustic-gravity mode covers the range of frequencies and horizontal wavelengths (0.03>~~>0.015 sec-', AH>SOOO km) where the spectral density of the observed solar oscillations, as calculated by Pierre Mein (Compt. Rend. 260, 1867, 1965), is large. It was also found that the height of the maximum vertical velocity shifts to greater altitudes as the frequency increases through the wide acoustic-gravity fundamental mode. This might explain the observed increase in the frequency of the oscillations with height.