Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C10019, doi:10.1029/2011JC007144.
Description:
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.
Description:
The data were collected with support from
NSF grant ECCS‐0308070 to SGM as part of the LOBO program (Ken
Johnson, P.I.). The analysis presented here was supported by the Department
of Defense (DoD) through the National Defense Science and Engineering
Graduate Fellowship (NDSEG) Program and through ONR grant N00014‐
10‐1‐0236 (Scientific officers: Thomas Drake, C. Linwood Vincent, and
Terri Paluszkiewicz). Additional support was provided by the Stanford
Graduate Fellowship (SGF).
Keywords:
Countergradient momentum fluxes
;
Nonequilibrium turbulence
;
Shallow tidal flow
;
Similarity scaling
;
Spectral lag
;
Turbulence spectra and cospectra
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
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