11.3.4. Isotropic instability rates

Present article of book is devoted to isotropic instability rates. The expressions for maximum rate of the instability have been defined. The considered theory of modulational interactions of broad wave packets allows to make the following conclusions: a) the instability is described by integral equations for perturbations of wave field correlation functions. These equations play the same role as the set of coupled equations for the fields of modulational perturbations in the case of a single monochromatic pump wave (or an infinite set of equations describing the modulational interactions of two modes). b) The instability of the broad wave spectrum is significantly suppressed compared with that of monochromatic pump wave of the same energy. c) The presence of the threshold of the modulational instability is possible only for sufficiently broad spectra, when the width of the spectra δω exceeds the maximum rate of the modulational instability.