On the Upper Ocean Turbulent Dissipation Rate due to Very Short Breaking Wind-Waves

TL;DR

This paper critically evaluates the contribution of micro-breakers and small whitecaps to ocean surface turbulence, concluding they are not significant contributors to the total dissipation rate, contrary to previous claims.

Contribution

It provides a reanalysis of existing data, challenging prior conclusions about the role of micro-breakers in ocean turbulence dissipation.

Findings

Micro-breakers and small whitecaps contribute minimally to total dissipation.

Total dissipation is mainly due to larger breaking waves.

Previous estimates overstate the role of micro-scale breakers.

Abstract

Sutherland and Melville (2015a) investigated the relative contributions to the total dissipation rate in the ocean surface wave boundary layer of different breaking wave scales, from large-scale whitecaps to micro-breakers. Based on their measurements of geometric/kinematic properties of breaking waves for a wide range of wave ages, they inferred the dissipation rates from breaking as a function of scale. These results were compared with their complementary measurements of the total dissipation rate in the underlying wave boundary layer. They reported that the total depth-integrated dissipation rate in the water column agreed well with dissipation rate from breaking waves for young to very old wind seas. They also reported high observed levels of dissipation rate very near the sea surface. They concluded that this showed a large fraction of the total dissipation rate was due to non-air entraining micro-breakers and very small whitecaps. Because of its fundamental importance, both physically and for accurate air-sea interaction modeling, we assess the validity of these conclusions. Our analysis of their data shows that the microbreakers and small whitecaps do not make a significant contribution to the total turbulent dissipation rate in the wave boundary layer.