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van Haren, Hans; Gostiaux, Louis

Distinguishing turbulent overturns in high-sampling-rate moored thermistor string observations

Journal of Marine Research, 73, 1-2, 17-32 (2015)

Turbulent overturns are distinguished from salinity-compensated intrusions in high-resolution moored thermistor string observations. The buoyancy frequency N is used to make the time dimensionless, "t*." This results in a primary, visual means to easily compare the duration of overturns with N, the natural frequency that separates internal waves from turbulent overturns.

As a secondary means, the shapes of overturns are investigated. Above various sloping topography between 500 and 1,000 m water depth where the buoyancy period varies between ∼1,300 and 2,600 s, vertical overturns of ∼40 m last Δt* =0.2–0.4. This corresponds with the timescale of growth of model-stratified turbulence in the wake of a grid. Smaller-scale, weaker-turbulent, shear-induced Kelvin-Helmholtz overturns of ∼5 m are observed to last approximately Δt* = 0.03, whereas the passage of their train of multiple consecutive overturns lasts up to approximately Δt* = 0.95. Although the shape of overturns can distinguish salinity-compensated intrusions from turbulent overturns, the present observations from internal wave breaking above sloping topography show complex results of mixed features.

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