Scaling turbulence in the ocean boundary layer of the Southeast Pacific Ocean stratus region

Una Miller, Lamont Doherty Earth Observatory, Palisades, NY, United States; Columbia University of New York, Earth and Environmental Sciences, New York, NY, United States, Christopher J Zappa, Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY, United States, J. Thomas Farrar, Woods Hole Oceanographic Inst, Department of Physical Oceanography, Woods Hole, MA, United States, Deborah A Le Bel, Lamont -Doherty Earth Observatory, Palisades, NY, United States and Robert A Weller, WHOI, Monument Beach, MA, United States
The rate of turbulence kinetic energy (TKE) dissipation (ε) is an important parameter in models of air-sea gas transfer and other ocean boundary layer (OBL) processes. Over the decades, semi-empirical parameterizations known as scaling relationships have been developed from boundary layer theory to allow for the approximation of ε from readily obtained meteorological variables. However, the spatial and temporal intermittency of turbulence as well as the difficulty of instrumenting the ocean have limited verification of these relationships. Here, we use data from a mooring in the stratus region of the Southeast Pacific Ocean to test published scaling relationships for ε. Measurements of ε were made using a pulse-to-pulse coherent Doppler sonar installed on the mooring line at a depth of 8.4 meters below the ocean surface, with accompanying measurements of meteorological and wave parameters. This dataset spans nine months which, to the best of our knowledge, represents the longest continuous time series that any scaling relationship for ε has been tested. We use the turbulence diagram proposed in Belcher et al. (2012) to show the dominance of buoyancy flux and wind shear over wind-wave interaction in generating turbulence at this site and find Monin-Obhukov (MO) similarity theory to perform well in these conditions. This suggests MO similarity is valid for use in ocean models that rely on ε to parameterize mixing processes in a convective-wind stress regime.