Bathymetry, stratification, and internal seiche structure

Fricker, Paul D.; Nepf, Heidi

doi:10.1029/2000jc900060

Cited by 63 publications

(69 citation statements)

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“…Fricker and Nepf (2000) showed that the magnification of currents and the location of a def- inite amplitude maximum somewhere over the middle of the slope depends on the structure of the stratification, unlike the flat-bottom case, where the maximum of bed velocity is always located in the middle of the basin. In similar fashion, the maximum bed velocity in the 3-D case is located away from the middle of the cell, where it would occur in a flatbottom Poincaré wave (Csanady 1967;Antenucci et al 2000).…”

Section: Discussionmentioning

confidence: 99%

“…16), located on the western slope. To do so, we calculated (following Fricker and Nepf 2000), at the elevation of each thermistor, the time series of temperature fluctuation with respect to the mean temperature profile in Fig. 5 and band passed this at the dominant observed periods, 24 and 12 h. Assuming that changes in temperature are due mainly to vertical displacement (i.e., assuming very small horizontal temperature gradients), the vertical displacement is give by…”

Section: Interaction Of the Wind And The Dominant Natural Modesmentioning

confidence: 99%

“…The structure of natural modes in a basin with a sloping bottom and a continuous stratification was studied numerically by Münnich (1996) and Fricker and Nepf (2000) for nonrotating, vertically two-dimensional basins with variable depth. They showed that the sloping bottom dramatically changes the spatial structure of the natural modes compared with those solutions obtained for a rectangular basin.…”

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confidence: 99%

“…They showed that the sloping bottom dramatically changes the spatial structure of the natural modes compared with those solutions obtained for a rectangular basin. Fricker and Nepf (2000) pointed out that an extension of their procedure to three dimensions (3-D) would be difficult.…”

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confidence: 99%

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Spatial structure of the dominant basin-scale internal waves in Lake Kinneret

2006

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Field data and numerical simulations were used to investigate the effects of basin shape, continuous stratification, and rotation on the three-dimensional structure of the dominant natural basin-scale internal-wave modes in Lake Kinneret, a stratified lake large enough so that the earth's rotation influences the wave motion. The structure of the modes was inferred from power spectral density of measured and simulated isotherm vertical displacements and from rotary-power spectral density of isopycnal velocities obtained from numerical simulations. The shape of the lake at the level of the thermocline, in conjunction with the dispersion relationship, determines the horizontal configuration of the natural modes. The dominant response to wind forcing was an azimuthal and vertical mode 1 Kelvin wave with a natural period of 22.6 h that propagated around the entire basin; the second most dominant response was a vertical mode 1 wave with a natural period close to 10.5 h and composed of two counter-rotating Poincaré circular cells. The sloping bottom produced an intensification of vertical displacements and velocities over the slope due to focusing of waves rays after reflection at bottom slopes close to the critical angle. The amplitude of the observed oscillations was very sensitive to the phase of the wind relative to the existing waves; resonance was affected by the cessation time of the wind events because it defines the local forcing period and resets the phase of the observed oscillations.

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Section: Discussionmentioning

confidence: 99%

Section: Interaction Of the Wind And The Dominant Natural Modesmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Spatial structure of the dominant basin-scale internal waves in Lake Kinneret

2006

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“…The height of such well-mixed layers varies between a few meters in lakes and reservoirs (Gloor et al 2000;Hondzo and Haider 2004;Lemckert et al 2004) to several tens of meters in oceans (Caldwell 1978;Lentz and Trowbridge 1991). The turbulent kinetic energy (TKE) required to generate and maintain such mixed layers is usually assumed to be produced by the bottom friction of basin-or large-scale currents (Fricker and Nepf 2000; Wüest et al 2000), shoaling and critical reflection of high-frequency internal waves (Thorpe 1997; Imberger 1998), or the interaction of large-scale currents with rough topography (Rudnick et al 2003).Enhanced mixing along the boundaries has been demonstrated in numerous studies (Macintyre et al 1999; Ledwell et al 2000;Garrett 2003). Moreover, tracer measurements in lakes (Goudsmit et al 1997) and ocean basins (Ledwell and Bratkovich 1995; Ledwell and Hickey 1995) revealed the potential importance of boundary mixing for basin-scale 1 To whom correpsondence should be addressed.…”

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Shear-induced convective mixing in bottom boundary layers on slopes

2005

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Field data from a stratified lake demonstrate that buoyancy-driven convective mixing can be an important mechanism for the formation of well-mixed bottom boundary layers (BBLs) on slopes. Convective turbulence is caused by differential transport of stratified water masses along the slope of a basin. Because the current velocity usually decreases toward the sediment, water at some distance from the bottom is transported faster than is water below. During upslope flow, this process leads to transport of heavier water on top of lighter water and hence to unstable stratification within the BBLs. Analogously, strong BBL stratification occurs during downslope flow. High-frequency acoustic Doppler current profiler (ADCP) and temperature measurements in the BBLs of a lake revealed the cyclic occurrence of convective turbulence driven by periodic across-slope currents of internal seiching. The estimated maximum buoyancy flux within the BBLs was in good agreement with the highest observed dissipation rates of turbulent kinetic energy. This suggests that, in our specific case, classical bottom shear production and the mentioned buoyancy-driven (convective) production contributed by similar amounts to the turbulent kinetic energy.It is a frequently observed feature of many stratified water bodies that a well-mixed bottom boundary layer (BBL) exists directly above the sediment surface. The height of such well-mixed layers varies between a few meters in lakes and reservoirs (Gloor et al. 2000;Hondzo and Haider 2004;Lemckert et al. 2004) to several tens of meters in oceans (Caldwell 1978;Lentz and Trowbridge 1991). The turbulent kinetic energy (TKE) required to generate and maintain such mixed layers is usually assumed to be produced by the bottom friction of basin-or large-scale currents (Fricker and Nepf 2000; Wüest et al. 2000), shoaling and critical reflection of high-frequency internal waves (Thorpe 1997; Imberger 1998), or the interaction of large-scale currents with rough topography (Rudnick et al. 2003).Enhanced mixing along the boundaries has been demonstrated in numerous studies (Macintyre et al. 1999; Ledwell et al. 2000;Garrett 2003). Moreover, tracer measurements in lakes (Goudsmit et al. 1997) and ocean basins (Ledwell and Bratkovich 1995; Ledwell and Hickey 1995) revealed the potential importance of boundary mixing for basin-scale 1 To whom correpsondence should be addressed. Present address: Limnological Institute, University of Konstanz, Mainaustrasse 252, D-78464 Konstanz, Germany (andreas.lorke@uni-konstanz.de). AcknowledgmentsWe thank M. Schurter and D. Finger for their great help in the field. The constructive input from two reviewers significantly improved the clarity of the manuscript; D. Richter, M. Schmid, and D. McGinnis provided helpful comments; and M. Stubbs kindly corrected the English.

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Movements of the thermocline lead to high variability in benthic mixing in the nearshore of a large lake

Chowdhury

Wells

Howell

2016

Water Resources Research

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The thermocline of Lake Ontario is in constant motion, and as it washes back and forth along the sloping lakebed there is a striking asymmetry in near‐bed stratification and benthic turbulence between its rise and fall. Detailed field observations of the stratification and water currents from the summers of 2012 and 2013 showed that the thermocline motions had large amplitudes (as high as 15 m) and a dominant period between 16 and 17.5 h, corresponding to a near‐inertial internal Poincaré wave. During the falling phase, the warmer down‐slope flow was strongly stratified with near‐bed water temperature gradients of 1°C m−1. In contrast during the rising phase of colder up‐slope flow, there was an unstable stratification in near‐bed water and large temperature overturns due to the differential advection of stratified waters, i.e., the shear‐driven convective mechanism. Using a Thorpe‐scale analysis of overturns, the inferred turbulent diffusivity during the up‐slope flow was Kz =5 × 10−4 m2 s−1. In striking contrast during the down‐slope flow, the strong stratification had lower turbulent diffusivities of Kz =10−6 m2 s−1. The near bottom region of Lake Ontario within the thermocline swash‐zone has intense biological activity and the highest concentrations of invasive dreissenid mussels. We discuss the potential biological implications of the striking variability in benthic mixing and near‐bed stratification for nutrient cycling in the Lake Ontario nearshore.

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Bathymetry, stratification, and internal seiche structure

Cited by 63 publications

References 31 publications

Spatial structure of the dominant basin-scale internal waves in Lake Kinneret

Spatial structure of the dominant basin-scale internal waves in Lake Kinneret

Shear-induced convective mixing in bottom boundary layers on slopes

Movements of the thermocline lead to high variability in benthic mixing in the nearshore of a large lake

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