Scale dependence of bubble creation mechanisms in breaking waves

Area of Science:

• Oceanography
• Fluid Dynamics
• Atmospheric Science

Background:

• Breaking ocean waves entrain air bubbles, significantly impacting air-sea gas flux, aerosol production, and ocean acoustics.
• The size distribution of these entrained bubbles is critical for controlling these processes, yet remains poorly understood within whitecaps.

Purpose of the Study:

• To measure bubble size distributions within breaking waves in both laboratory and open ocean settings.
• To quantitatively describe the mechanisms responsible for bubble formation inside whitecaps.

Main Methods:

• In-situ measurements of bubble size distributions were conducted in laboratory-generated breaking waves.
• Field measurements were performed in the open ocean to capture natural breaking wave conditions.
• Analysis focused on identifying distinct bubble formation mechanisms based on size.

Main Results:

• Two primary mechanisms govern bubble size distribution: turbulent fragmentation for bubbles >1 mm (density ~ R^-10/3) and jet/drop impacts for smaller bubbles (density ~ R^-3/2).
• The Hinze scale, where turbulent fragmentation ceases, demarcates the transition between these two size-controlling processes.
• A quantitative description of bubble formation mechanisms was established.

Conclusions:

• Bubble size distribution in breaking waves is determined by a combination of turbulent fragmentation and jet/drop impact mechanisms.
• Understanding these mechanisms and the associated Hinze scale is crucial for accurately modeling air-sea gas transfer.
• The findings have significant implications for climate modeling and understanding ocean-atmosphere interactions.