Discrete exact and quasi-resonances of Rossby/drift waves on $\b$-plane with periodic boundary conditions

TL;DR

This paper clarifies the nature of resonance clustering in Rossby/drift waves on a $eta$-plane, showing the absence of isolated triads and highlighting the importance of quasi-resonances in energy transport.

Contribution

It resolves discrepancies between numerical and analytical results by identifying pitfalls in previous numerical studies and characterizes the unique resonance clustering structure in this wave system.

Findings

No isolated triads in resonance clustering

Smallest cluster contains 6 interconnected triads

Quasi-resonances significantly influence energy transport

Abstract

Analysis of resonance clustering in weakly nonlinear dispersive wave systems, also called discrete wave turbulent systems, is a new methodology successfully used in the last years for characterizing energy transport due to exact and quasi-resonances. Quite recently this methodology has been used in the paper by M. D. Bustamante, U. Hayat "Complete classification of discrete resonant Rossby/drift wave triads on periodic domains", \cite{BH13}, in order to show that resonance clustering is very sparse and quasi-resonances (that is, resonances with small enough detuning) play major role in the energy transport in this specific wave system. On the other hand, in the paper by M. Yamada, T. Yoneda "Resonant interaction of Rossby waves in two-dimensional flow on $\beta$-plane", \cite{YaYo13}, the same physical system is studied and a mathematically rigorous theorem is proven: at high $\b$, the flow dynamics is governed exclusively by resonant interactions. In our present paper we demonstrate that this seeming contradiction between numerical results \cite{BH13} and analytical results \cite{YaYo13} are due to some pitfalls in numerical studies of exact and quasi-resonances presented in \cite{BH13}. We also demonstrate that resonance clustering of drift waves on periodic $\b$-plane differs substantially from characteristic resonance clustering in other 3-wave systems: instead of a usual set of isolated triads and a few bigger clusters, there exists \emph{no isolated triads} in this case. Resonant triads are interconnected in a complicated way and the smallest cluster consists of 6 connected triads.