Parametric interaction and intensification of nonlinear Kelvin waves

TL;DR

This paper presents observational evidence of nonlinear interactions between mesoscale Kelvin waves and synoptic oscillations in the Japan/East Sea, suggesting energy transfer mechanisms that may influence larger climate phenomena like El Niño.

Contribution

It introduces a new observational analysis of nonlinear Kelvin wave interactions with synoptic oscillations, and develops a theoretical model for their parametric interaction.

Findings

Enhanced coastal currents at sum and difference frequencies exhibit Kelvin wave properties.

Nonlinear interactions may cause intensification and breaking of Kelvin waves.

Potential implications for understanding El Niño dynamics.

Abstract

Observational evidence is presented for nonlinear interaction between mesoscale internal Kelvin waves at the tidal -- $\omega_t$ or the inertial -- $\omega_i$ frequency and oscillations of synoptic -- $\Omega $ frequency of the background coastal current of Japan/East Sea. Enhanced coastal currents at the sum -- $\omega_+ $ and dif -- $\omega_-$ frequencies: $\omega_\pm =\omega_{t,i}\pm \Omega$ have properties of propagating Kelvin waves suggesting permanent energy exchange from the synoptic band to the mesoscale $\omega_\pm $ band. The interaction may be responsible for the greater than predicted intensification, steepen and break of boundary trapped and equatorially trapped Kelvin waves, which can affect El Ni\~{n}o. The problem on the parametric interaction of the nonlinear Kelvin wave at the frequency $\omega $ and the low-frequency narrow-band nose with representative frequency $\Omega\ll\omega $ is investigated with the theory of nonlinear week dispersion waves.