Bubbles in the Near-Surface Ocean: Their Various Structures

Jin Wu Air-Sea Interaction Laboratory, Graduate College of Marine Studies, University of Delaware, Lewes, Delaware

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Abstract

Air is entrained by breaking waves to produce bubbles. A highly transient macrobubble cloud is first generated under the breaker, with larger bubbles returning sooner to the sea surface. Those remaining smaller bubbles are then dispersed by near-surface turbulent shear flows in a shallow layer immediately below the undulating sea surface. Bubbles in this layer are shown to be nearly suspended; moreover, vertical distributions of current velocity and bubble concentration within this layer are found to be similar. Both of these features are used to demonstrate that the observed bubble layer, being on the order of 1 m thick, is formed through the longitudinal dispersion process. In addition, isolated microbubble plumes that penetrate several times deeper than the bubble layer appear to be produced also by breaking waves; however, in this case breaking waves temporarily deflect the bubble layer.

Abstract

Air is entrained by breaking waves to produce bubbles. A highly transient macrobubble cloud is first generated under the breaker, with larger bubbles returning sooner to the sea surface. Those remaining smaller bubbles are then dispersed by near-surface turbulent shear flows in a shallow layer immediately below the undulating sea surface. Bubbles in this layer are shown to be nearly suspended; moreover, vertical distributions of current velocity and bubble concentration within this layer are found to be similar. Both of these features are used to demonstrate that the observed bubble layer, being on the order of 1 m thick, is formed through the longitudinal dispersion process. In addition, isolated microbubble plumes that penetrate several times deeper than the bubble layer appear to be produced also by breaking waves; however, in this case breaking waves temporarily deflect the bubble layer.

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