Waves in the Solar Atmosphere. II. Large-Amplitude Acoustic Pulse Propagation

Numerical experiments are performed with vertically propagating acoustic pulses by solving the nonlinear equations of fluid motion using a finite-difference technique. The pulse energy, dissipation, wake, and atmospheric heating are investigated, and the results compared with weak- shock theory. The ratio of pulse frequency to the acoustic cutoff frequency, N = yg/2c, is found to be a crucial parameter. Weak-shock theory gives reasonable results for pulse widths less than 50 seconds (w > 2N ), but greatly overestimates the pulse energy and dissipation for longer pulses. Significant dissipation begins at the height where the crest of a simple wave overtakes its trough. For pulses with a) > 2 the minimum damping length is about 500 km and occurs at about 1000 km above T5000 = 1. For lower-frequency pulses the minimum damping length is about 1000 km and occurs higher up. Until hydrogen is nearly completely ionized, ionization and radiation keep the temperature rise small.