The nonlinear effects of the eddy viscosity and the bottom friction on the Lagrangian residual velocity in a narrow model bay

2017 ◽  
Vol 67 (9) ◽  
pp. 1105-1118 ◽  
Author(s):  
Fangjing Deng ◽  
Wensheng Jiang ◽  
Shizuo Feng
Keyword(s):  
Eddy Viscosity ◽  
Nonlinear Effects ◽  
Bottom Friction ◽  
Residual Velocity ◽  
Lagrangian Residual Velocity

Note on wind drift in a channel in the presence of tidal currents

1953 ◽  
Vol 219 (1139) ◽  
pp. 426-446 ◽  
Keyword(s):  
Steady State ◽  
Drift Velocity ◽  
Wind Stress ◽  
Eddy Viscosity ◽  
Tidal Currents ◽  
Bottom Friction ◽  
Convergent Channel ◽  
Tidal Period ◽  
Uniform Channel ◽  
Wind Currents

In waters such as those surrounding the British Isles, wind currents appear as perturbations superimposed on the tidal currents. In treating this problem, it is assumed that the drift velocity is small compared with the amplitude of the tidal current. In this case, if the instantaneous value of the bottom friction is proportional to the square of the instantaneous velocity, the non-periodic component of friction, averaged over a tidal period, is linearly proportional to the drift velocity. It is assumed that the water is homogeneous and that, above a skin-friction layer close to the bottom, the eddy viscosity is constant with depth. In the steady state, the drift current due to a given wind stress is reduced in the presence of tidal currents. Steady-state solutions, involving the elevation of the surface as well as the currents, are given for a channel of uniform width and depth, a uniformly convergent channel and a non-uniform channel. Numerical calculations, based on the most probable estimates of wind stress, eddy viscosity and bottom friction available at present, are given for several particular cases. A discussion is given of their application to drift currents and surface gradients in the English Channel, a region in which it is proposed to carry out a programme of observations in the near future.

Tilted drifting jets over a zonally sloped topography: effects of vanishing eddy viscosity

2019 ◽  
Vol 876 ◽  
pp. 939-961
Author(s):  
Hemant Khatri ◽  
Pavel Berloff
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Bottom Topography ◽  
Principal Component ◽  
Bottom Friction ◽  
Nonlinear Interactions ◽  
Multiple Jets ◽  
Spatio Temporal ◽  
Friction Parameters

Oceanic multiple jets are seen to possess spatio-temporal variability imposed by varying bottom topography resulting in jets that can drift and merge. The dynamics of multiple jets over a topographic zonal slope is studied in a two-layer quasi-geostrophic model. The jets tilt from the zonal direction and drift meridionally. In addition to the tilted jets, other large-scale spatial patterns are observed, which are extracted using the principal component analysis. The variances of these patterns are strongly influenced by the values of eddy viscosity and bottom friction parameters. The contribution of the tilted jets to the full flow field decreases with decreasing friction and viscosity parameters, and purely zonal large-scale modes, propagating in the meridional direction, populate the flow field. Linear stability analysis and two-dimensional kinetic-energy spectrum analysis suggest that the zonal modes gain energy from ambient eddies as well as from the tilted jets through nonlinear interactions. However, viscous dissipation and bottom friction tend to suppress the nonlinear interactions, which results in the inhibition of the upscale energy transfer from eddies to the zonal modes. These simulations suggest that, in the presence of topography, alternating jet patterns may be sustained through interactions among various large-scale modes. This is different from the classical zonal jet formation arguments, in which direct eddy forcing maintains the jets.

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