Bubble‐induced turbulence suppression in Langmuir circulation

Abstract

Dissipation rates ϵof turbulent kinetic energy and air bubble characteristics were observed within the wave‐enhanced near‐surface layer in the open ocean. During a period of well developed Langmuir circulation, short periods of increased air fraction and peak bubble radii <150μm at 2.5m, indicative of the instrumentation package drifting through convergence zones, coincide with significantly reduced dissipation rates. The rate of turbulence suppression correlates well with the buoyancy frequency inferred from the vertical gradient of air fraction. The Ozmidov scale and turbulent time scales associated with the bubble induced stratification are of O(0.5m) and O(20–60s), respectively. These stratification characteristics are consistent with the suppression of energy containing eddies close to the surface, which in turn results in reduced turbulent dissipation rates. Dissipation rates are observed to decay with depth following a power law ϵ ∝ zn, and n = −1, consistent with the theoretical value for constant stress layer scaling, is found within convergence zones, but n ≈ −3 outside.