Sound fluctuations resulting from mode coupling in shallow-water internal waves

We conduct a theoretical analysis and numerical simulation of fluctuations of low-frequency signals propagating in shallow water in the presence of nonlinear internal waves moving approximately along the acoustic track. It is believed that mode coupling causes the fluctuations. We show that in the fluctuation spectra there are characteristic frequencies that are proportional to the motion velocity of solitons along the track. We calculate the sound field using single- and multimode sources and analyze the frequency-mode composition of the field responsible for the maximum and minimum fluctuations. We analyze the so-called dominant fluctuation frequency introduced previously by the authors, which corresponds to fluctuations with the maximum amplitude in the given frequency range and for the given set of modes. We compare the calculation results with estimates obtained previously by the authors within the framework of ray theory.