The term infrasound is applied to low frequency sound in the atmosphere, generally below the limit of human hearing. The frequencies of interest in our research range from 10 Hz down to as low as 0.001 Hz, corresponding to periods of 0.1 to 1000 seconds. Such signals tend to be geophysical in nature, propagating globally and generated by large, violent events such as hurricanes, tornadoes, earthquakes and nuclear weapon detonation. Their propagation depends critically on large scale temperature and wind velocity gradients. These produce a variety of acoustic ducts in the atmosphere. These are asymmetric with respect to azimuth and interact with each other. They are also spatially and temporally varying, with small scale fluctuations on top of diurnal and seasonal cycles. An overview of sources, generation and propagation of infrasound in the atmosphere will be presented.

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