Microbarom
[5][11] The reason for the discovery of this phenomenon was an accident: the aerologists working at the marine Hydrometeorology stations and watercraft drew attention to the strange pain that a person experiences when approaching the surface of a standard meteorological probe (a balloon filled with hydrogen).
This phenomenon drew genuine interest among scientists; in order to study it, special equipment was designed to record powerful but low-frequency vibrations that are not audible to human ears.
Microbaroms were first described in United States in 1939 by American seismologists Hugo Benioff and Beno Gutenberg at the California Institute of Technology at Pasadena, based on observations from an electromagnetic microbarograph,[11] consisting of a wooden box with a low-frequency loudspeaker mounted on top.
[12] They noted their similarity to microseisms observed on seismographs,[9] and correctly hypothesized that these signals were the result of low pressure systems in the Northeast Pacific Ocean.
[9] Following up on the theory of microseisms by M. S. Longuet-Higgins, Eric S. Posmentier proposed that the oscillations of the center of gravity of the air above the Ocean surface on which the standing waves appear were the source of microbaroms, explaining the doubling of the ocean wave frequency in the observed microbarom frequency.
The first quantitatively correct theory of microbarom generation is due to L. M. Brekhovskikh who showed that it is the source of microseisms in the ocean that couples to the atmosphere.
[18] Studies have shown that the coupling produces propagating atmospheric waves only when non-linear terms are considered.
[9] Microbaroms are a form of persistent low-level atmospheric infrasound,[22] generally between 0.1 and 0.5 Hz, that may be detected as coherent energy bursts or as a continuous oscillation.
Rays directed vertically toward the zenith are dissipated in the thermosphere, and are a significant source of heating in that layer of the upper atmosphere.
[26] At mid latitudes in typical summer conditions, rays between approximately 30 and 60 degrees from the vertical are reflected from altitudes above 125 km where the return signals are strongly attenuated first.
[8] Microbaroms are a significant noise source that can potentially interfere with the detection of infrasound from nuclear explosions.
Accurate detection of explosions is a goal of the International Monitoring System organized under the Comprehensive Nuclear-Test-Ban Treaty (which has not entered into force).
