Published In
Journal of Physical Oceanography
Document Type
Article
Publication Date
7-25-2016
Subjects
Columbia River (Or. And Wash.) -- Tides -- Analysis, Plumes (Fluid dynamics) -- Mathematical models, Shear flow -- Mathematical models
Abstract
Considerable effort has been made to parameterize turbulent kinetic energy (TKE) dissipation rate εand mixing in buoyant plumes and stratified shear flows. Here, a parameterization based on Kunze et al. is examined, which estimates ε as the amount of energy contained in an unstable shear layer (Ri < Ric) that must be dissipated to increase the Richardson number Ri = N2/S2 to a critical value Ric within a turbulent decay time scale. Observations from the tidal Columbia River plume are used to quantitatively assess the relevant parameters controlling ε over a range of tidal and river discharge forcings. Observed ε is found to be characterized by Kunze et al.’s form within a factor of 2, while exhibiting slightly decreased skill near Ri = Ric. Observed dissipation rates are compared to estimates from a constant interfacial drag formulation that neglects the direct effects of stratification. This is found to be appropriate in energetic regimes when the bulk-averaged Richardson number Rib is less than Ric/4. However, when Rib > Ric/4, the effects of stratification must be included. Similarly, εscaled by the bulk velocity and density differences over the plume displays a clear dependence on Rib, decreasing as Rib approaches Ric. The Kunze et al. ε parameterization is modified to form an expression for the nondimensional dissipation rate that is solely a function of Rib, displaying good agreement with the observations. It is suggested that this formulation is broadly applicable for unstable to marginally unstable stratified shear flows.
DOI
10.1175/JPO-D-15-0156.1
Persistent Identifier
http://archives.pdx.edu/ds/psu/18240
Citation Details
Jurisa, J. T., Nash, J. D., Moum, J. N., Kilcher, L. F., Jurisa, J. T., Nash, J. D., … Kilcher, L. F. (2016). Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume. Journal of Physical Oceanography, 46(8), 2373–2388.
Description
To the best of our knowledge, this work was authored as part of the Contributor's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.