Similarity scaling of turbulence spectra and cospectra in a shallow tidal flow

Abstract

[1] Measured turbulence power spectra, cospectra, and ogive curves from a shallow tidal flow were scaled using Monin-Obukhov similarity theory to test the applicability to a generic tidal flow of universal curves found from a uniform, neutrally stable atmospheric boundary layer (ABL). While curves from individual 10 min data bursts deviate significantly from similarity theory, averages over large numbers of sufficiently energetic bursts follow the general shape. However, there are several differences: (1) Variance in the measured curves was shifted toward higher frequencies, (2) at low frequencies, velocity spectra were significantly more energetic than theory while cospectra were weaker, and (3) spectral ratios of momentum flux normalized by turbulent kinetic energy (TKE) indicate decreased fluxes and/or elevated TKE levels. Several features of the turbulence structure may explain these differences. First, turbulent dissipation exceeded production, indicating nonequilibrium turbulence, possibly from advection of TKE. Indeed, using the production rate rather than dissipation markedly improves agreement in the inertial subrange. Second, spectral lag of the largest eddies due to inhomogeneous boundary conditions and decaying turbulence could explain spectral deviations from theory at low frequencies. Finally, since the largest eddies dominate momentum transfer, the consequence of the cospectra difference is that calculated ogive curves produced smaller total momentum fluxes compared to theory, partly because of countergradient fluxes. While ABL similarity scaling applied to marine bottom boundary layers (MBBLs) will produce curves with the general shape of the universal curves, care should be taken in determining details of turbulent energy and stress estimates, particularly in shallow and inhomogeneous MBBLs.

On the wave and current interaction with a rippled seabed in the coastal ocean bottom boundary layer

“…[]. While these were derived for a neutrally stable atmospheric boundary layer, they have been applied before to oceanic boundary layers as well [e.g., Soulsby , ; Walter et al ., ]. The Kaimal cospectrum is where is the nondimensional frequency.…”

“…Consequently, field measurements within the inner region of the BBL to complement the laboratory studies are essential. Such measurements have been performed using profiling thermistors [ Caldwell and Chriss , ; Chriss and Caldwell , ], hot film anemometer arrays [ Foster et al ., , 2006], laser Doppler velocimeters [ Agrawal and Aubrey , ; Trowbridge and Agrawal , ], acoustic Doppler velocimeters [ Davis and Monismith , ; Feddersen et al ., ; Walter et al ., ], acoustic current meters [ Trowbridge , ; Williams et al ., ], and coherent Doppler profilers [ Lacy et al ., ; Hay , ; Zou et al ., ]. Our group has introduced the application of 2‐D particle image velocimetry (PIV) to resolve the flow in the inner part of the BBL, achieving 4–5 mm resolution over sample areas ranging from 20 × 20 cm 2 to 50 × 50 cm 2 [ Bertuccioli et al ., ; Doron et al ., ; Hackett et al ., ; Luznik et al ., ; Nimmo Smith et al ., , 2005].…”

Nearshore internal bores and turbulent mixing in southern Monterey Bay

“…Conventional estimates of turbulent dissipation with moored instruments have significant issues in coastal zones due to small velocities with a high noise floor and wave contamination. Likewise, wave‐turbulence separation methods for estimating turbulent stresses and shear production (and ultimately dissipation assuming equilibrium turbulence) from ADCPs are also affected by waves [e.g., Rosman et al , 2008; Kirincich et al , 2010], with wave‐turbulence separation methods often not appropriate in certain environments [ Walter et al , 2011]. However, the technique of using isopycnal slope spectra to estimate dissipation rates does not suffer significantly from surface wave contamination and may be appropriate for use in coastal waters with strong wave signatures [e.g., Woodson et al , 2011].…”

Inclusion of Increased Air Turbulence Caused by Coke Production into Atmospheric Propagation Modelling

“…This turbulence of limited energy is conveyed inland along the mean velocity vectors of the wind (Panofsky et al 1982). Similar studies were conducted in marshy areas (Walter et al 2011). Analogical measurements at city boundaries and on flat areas with no significant terrain obstacles are described in Högström et al (1982).…”