Mode coupling and sound field variability in near-coastal area in the presence of internal Kelwin waves

In this paper, propagation of the sound waves in near-coastal wedge-like area is studied in the presence of Internal Kelwin waves (IKW), which cause periodic changes of the thermocline level with daily period. These oscillations initiate variation of the sound field interference structure at the receiving system. In the paper theoretical analysis and numerical modeling of these fluctuations are carried out, it is shown that physical reason of variability of the sound field is specific mode coupling in area where time and range depending eigen values of adiabatic modes are closing to each other (quasi-crossection) in a wedge-like waveguide, periodical displacement of place of this quasi-crossection initiates fluctuations of the sound field. Calculations of modal amplitudes and in turn structure and spatio-temporal variability of the sound field in a waveguide was carried out within the framework of parabolic equation and solution of system of equations of mode coupling. Results are compared with experimental data. [Work was supported by RFBR, Grant 20-05-00119.]