Cyclone interacts with maritime storm

by Martha W. Burke

Infrasonics involves the study of acoustic radiation at frequencies below the range of human hearing. Acoustic energy refers to the presence of elastic longitudinal waves in a uid. Displacement of a boundary surface or localized compression or rarefaction causes a disturbance of the particle locations within the uid. Such displacement results in a restoring force on the particles which can produce traveling waves in an unbounded uid or standing waves in a contained uid. The human ear can detect sound with frequencies as low as 20 Hz, and the human body can sense vibrations at even lower frequencies. This 20 Hz threshold denes the upper limit of infrasonic frequencies. Infrasound can be generated by both natural and anthropomorphic sources. Severe weather, surf, avalanches, earthquakes, bolides, aurorae, and lightning are known to produce natural infra sound. Sonic booms, chemical and nuclear explosions, and large machinery are known sources of man-madem infra sound.