The generation of a difference harmonic attending the vertical propagation in the atmosphere of two acoustic waves of close frequency is considered. Pumping of energy from the difference to the primary harmonic is possible at a certain distance from the source. The energy of the difference harmonic, after formation of a discontinuity in the primary radiat ion, tends to some constant value, determined by the ratio of the difference and fundamental frequencies. It is found that nonlinear effects manifest themselves in acoustic waves only at Mach numbers higher than some constant quantity, which depends on the values of the Knudsen number for the atmosphere.
Faculty of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia