Numerical analysis of breather interactions

While the existence of breathers in the ocean is not clearly revealed, Rouvinskaya et al. (2015) suggested the possibility that breathers occurred in the Baltic Sea. In three-layer symmetric stratifications with the same density difference across each interface, the modified KdV equation (the Gardner equation with the quadratic nonlinear coefficient equal to zero) predicts that breathers exist. Therefore, the soliton-like characteristics of fully nonlinear breathers must be better understood. Thus, this study used fully nonlinear numerical simulations to investigate breather interactions by analysing overtaking collisions of two breathers in a three-layer fluid. As a result, an overtaking collision of two breathers is almost elastic when the ratio of the breather amplitude to the upper and lower layer thickness is smaller. Furthermore, the collision is found to remove the mode-2 structure, resulting in a significant role in forming breathers.