A possible generation mechanism for internal waves near the edge of a submesoscale eddy

Abstract

Recently, it has been shown for the first time by observations that an anticyclonic mesoscale eddy can generate internal waves (wavelengths of 0.4 to 1 km) that carry energy away from the eddy. In the present study, we investigate a possible mechanism for generating internal waves near the edge of a submesoscale eddy. The study was motivated by airborne infrared imagery that shows curved thermal bands (wavelengths ∼70 m) near the edge of a 1-km-diameter cyclonic eddy. We hypothesize that these bands represent internal wave wakes generated by turbulent perturbations having scales of a few tens of meters that are advected along the eddy’s thermal perimeter. An analytical theory is developed to investigate this for an idealized perturbation advected by a circular current. Calculations show that, for a reasonable choice of parameter values, an internal wave wake develops around the eddy that has spiral-like phase lines resembling the orientations and wavelengths of the field observations. The general validity of our proposed mechanism should be verified with further studies.

Keywords

• submesoscale eddy
• internal waves
• thermal bands
• spiral-like phase lines