Rossby wave radiation by an eddy on a beta-plane: Experiments with laboratory altimetry

TL;DR

This study investigates Rossby wave radiation from vortices in a laboratory beta-plane setup, combining experiments, simulations, and linear theory to understand wave patterns and vortex dynamics.

Contribution

It provides new experimental evidence and analysis of Rossby wave radiation by vortices, linking laboratory results with numerical simulations and theoretical predictions.

Findings

Vortices travel northwest and radiate Rossby waves.

Vortices develop a dipolar component enabling translation.

Wavenumber related to vortex speed matches Rhines scale.

Abstract

Results from the laboratory experiments on the evolution of vortices (eddies) generated in a rotating tank with topographic beta-effect are presented. The surface elevation and velocity fields are measured by the Altimetric Imaging Velocimetry. The experiments are supplemented by shallow water numerical simulations as well as a linear theory which describes the Rossby wave radiation by travelling vortices. The cyclonic vortices observed in the experiments travel to the northwest and continuously radiate Rossby waves. Measurements show that initially axisymmetric vortices develop a dipolar component which enables them to perform translational motion. A pattern of alternating zonal jets to the west of the vortex is created by Rossby waves with approximately zonal crests. Energy spectra of the flows in the wavenumber space indicate that a wavenumber similar to that introduced by Rhines for turbulent flows on the beta-plane can be introduced here. The wavenumber is based on the translational speed of a vortex rather than on the root-mean-square velocity of a turbulent flow. The comparison between the experiments and numerical simulations demonstrates that evolving vortices also emit inertial waves. While these essentially three-dimensional waves can be observed in the altimetric data they are not accounted for in the shallow water simulations.