Surface Wave Effects on High-Frequency Currents over a Shelf Edge Bank

Abstract

Several acoustic Doppler current profilers and vertical strings of temperature, conductivity, and pressure sensors, deployed on and around the East Flower Garden Bank (EFGB), were used to examine surface wave effects on high-frequency flows over the bank and to quantify spatial and temporal characteristic of these high-frequency flows. The EFGB, about 5-km wide and 10-km long, is located about 180-km southeast of Galveston, Texas, and consists of steep slopes on southern and eastern sides that rise from water depths over 100 m to within 20 m of the surface. Three-dimensional flows with frequencies ranging from 0.2 to 2 cycles per hour (cph) were observed in the mixed layer when wind speed and Stokes drift at the surface were large. These motions were stronger over the bank than outside the perimeter. The squared vertical velocity w 2 was strongest near the surface and decayed exponentially with depth, and the e-folding length of w 2 was 2 times larger than that of Stokes drift. The 2-h-averaged w 2 in the mixed layer, scaled by the squared friction velocity, was largest when the turbulent Langmuir number was less than unity and the mixed layer was shallow. It is suggested that Langmuir circulation is responsible for the generation of vertical flows in the mixed layer, and that the increase in kinetic energy is due to an enhancement of Stokes drift by wave focusing. The lack of agreement with open-ocean Langmuir scaling arguments is likely due to the enhanced kinetic energy by wave focusing.

Sediment Resuspension and Transport by Internal Solitary Waves

“…Here, the drawdown of the pycnocline and subsequent generation of upslope-propagating boluses have the potential to induce BBL turbulence and resuspension (Figure 7c). The effect of surface wave-induced currents is nonnegligible in this region (e.g., Wijesekera et al 2013), but this effect remains unexplored in simulations. Boluses have been modeled by several authors, with 3D simulations by Arthur & Fringer (2014) providing…”

Observations on stratified flow over a bank at low Froude numbers

“…High values of ε , which easily reached 10 −6 W kg −1 , were also found near the bottom of the EFGB as well as near the sea surface (above 10 m; Figures and ). Near‐surface turbulence seemed to be partially related to the daily temperature cycle since winds were rather weak and surface waves were small and not breaking (surface wave significant heights were less than 0.5 m [ Wijesekera et al ., ]). Additionally, estimates of the Kolmogorov scale ( L O = ε 1/2 N − 3/2 ) indicated that length scales of turbulent overturns in the EFGB region were less than 1 m (99% of L O estimates ≤ 1).…”

Profiling Dissipation Measurements using (chi)pods on Moored Profilers in Luzon Strait

“…This experiment builds on technicalscientific relationships established with NRL for the Mixing Over Rough Topography experiment in the Gulf of Mexico (MORT; Wijesekera et al, 2013).…”