Atmospheric Acoustic Gravity Modes at Frequencies Near and Below Low Frequency Cutoff Imposed by Upper Boundary Conditions,

摘要

Perturbation techniques are described for the computation of the imaginary part of the horizontal wave number (k sub I) for modes of propagation. Numerical studies were carried out for a model atmosphere terminated by a constant sound speed (478m/sec) half space above an altitude of 125 km. The GR(0) and GR(1) modes have lower frequency cutoffs. It was found that for frequencies less than 0.0125 radian/sec, the GR(1) mode has complex phase velocity; K sub I varying from near zero up to a maximum of 0.0003 with analogous results for the GR(0) mode. There is an extremely small frequency gap for each mode for which no poles in the complex k plane corresponding to that mode exist. These mark the transition from undamped propagation to damped propagation. In the complete Fourier synthesis, branch line contributions compensate for the absence of poles in these gaps. Computational procedures are described which facilitate the inclusion of the low frequency portions of these modes in the waveform synthesis. (Author)