Excitation of acoustic-gravity waves In an isothermal atmosphere

The excitation of acoustic-gravity waves in an isothermal atmosphere is considered in this paper. It is shown that the excitation due to mass production, momentum production and heat production can be discussed by examining the same differential equation. The sources are assumed to be extended and vary both in time and in space. Asymptotic methods are used to obtain analytic expressions for the radiation field for all times, from the arrival of precursors to any time thereafter. It is found that the transient response results from contributions from one, two or all three modes depending on the times from the arrival of precursors. The three modes are the high frequency acoustic mode, the intermediate frequency buoyancy mode and the low frequency gravity mode. Additional features of the transient behavior depend on the temporal as well as spatial variation of the sources. An example is given for which numerical computations are made. Possible applications of the results to geophysical problems are duscussed and certain extensions of the results are proposed.