Infrasound

A new global network of microbarometers is breathing life into a once dormant branch of acoustics: the study of infrasound. The nascent study of sub‐audible sounds is shedding new light on a great variety of man‐made and natural phenomena in the atmosphere, including Mount Saint Helens, pictured on the front cover of this issue. The re‐emergence of this field is due largely to the Comprehensive Nuclear‐Test‐Ban Treaty (CTBT), which was opened for signatures in New York City in September of 1996. The CTBT held the promise of limiting the spread of nuclear weapons. In the process, the treaty created the International Monitoring System (IMS). The International Monitoring System consists of seismic, hydroacoustic, radionuclide, and sixty infrasound stations spread over the globe to provide almost uniform coverage (Fig. 1).