Abstract (Invited)

Nonlinear Acoustic Phenomena in Atmosphere

S.N.Kulichkov (Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russia)

e-mail: snk@omega.ifaran.ru

The nonlinear acoustic phenomena in atmosphere are studied. Samples of evidence for nonlinear atmospheric effects in long-range infrasound propagation from explosions of different types and yields are presented. A short historical review and an analysis of the current status of both theoretical and experimental studies of long-range sound propagation in the atmosphere are given. The fact that the "acoustic pulse" I - the product of the wave profile area S in the coordinates p (pressure) and t (time) by the distance to the source r - is conserved during long-range infrasound propagation in the atmosphere is experimentally supported. The results of the experiments on recording infrasonic waves at long (up to 300 km) distances from different (underground, ground, and air) explosions equivalent to 100 kg - 2000 t of TNT and realized in different geographical regions in different seasons are analyzed. The obtained empirical ratio I0=0.616*I^0.988 allows one to estimate the initial value of the "acoustic pulse" I0 in the vicinity of its source from the data on infrasound arrivals recorded within the audibility zone at long distances from explosion. Within the audibility zone, the obtained expression can be used for the stratospheric, mesospheric, and thermospheric infrasound arrivals at any distances from explosions. The empirical ratio E0[kt]=1.38*10^(-10)*(I[kg/s])^1.482 is proposed to determine the energy E (in kt of TNT) of an equivalent explosion from the records of acoustic signals at long distances from sources without regard to the type of ray trajectories. On the basis of the phenomenon of acoustic pulse conservation during long-range infrasound propagation in the atmosphere, the ratio df/f ~ dp/p is proposed. This ratio allows one, for a given distance r, to estimate the error df in determining the frequency of the spectral maximum of signal f, which approximately corresponds to the error dp in determining the acoustic pressure in the infrasonic arrivals from explosions. [This work was supported in part by the RFBR, project 02-05-65112].

Section : 6