Scaling of moored surface ocean turbulence measurements in the Southeast
Pacific Ocean
Abstract
Estimates of turbulence kinetic energy (TKE) dissipation rate (ε) are
key to understanding how heat, gas, and other climate-relevant
properties are transferred across the air-sea interface and mixed within
the ocean. A relatively new method involving moored pulse-coherent
Acoustic Doppler Current Profilers (ADCPs) allows for estimates of ε
with concurrent surface flux and wave measurements across an extensive
length of time and range of conditions. Here, we present 9 months of
moored estimates of ε at a fixed depth of 8.4m at the Stratus mooring
site (20°S, 85°W). We find that shear- and buoyancy-dominant turbulence
regimes are defined equally well using the Obukhov length scale (
LM ) and the newer Langmuir stability length scale
(LL ), suggesting that ocean-side friction velocity
(u*) implicitly captures the influence of Langmuir
circulation at this site. This is illustrated by a strong linear
dependence between surface Stokes drift (us) and and is
likely facilitated by the steady Southeast trade winds regime. The
traditional Law of the Wall (LOW) and surface buoyancy flux scalings of
Monin-Obukhov similarity theory scale our estimates of well, collapsing
data points near unity. We find that the newer Stokes drift scaling (
usu*2 /mixed layer depth) scales ε
well at times but is overall less consistent than LOW. Scaling
relationships from prior studies in a variety of aquatic and atmospheric
settings largely agree with our data in destabilizing, shear-dominant
conditions but diverge in other regimes.