Wind effect on diurnal thermally driven flow in vegetated nearshore of a lake

Lin, Ying-Tien

doi:10.1007/s10652-014-9368-x

Cited by 10 publications

(10 citation statements)

References 25 publications

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“…Further efforts have been paid to incorporate the vertical variation of horizontal velocities in the depth-integrated models [35,36], but the vertical stratification has yet to be addressed. Lin and Wu [37,38] and Lin [39] examined thermally-driven flows over vegetated sloping bottoms with an idealized, linear, vertically-solved slice analytical model. It was reported that vegetation can significantly change the circulation pattern of the open water zone to a large extent.…”

Section: Introductionmentioning

confidence: 99%

Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Torma

2019

Water

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In this paper, the effects of littoral submerged macrophytes on weak stratification conditions in a small and shallow lake are investigated. Diverse submerged macrophytes occupying a large portion of the littoral zone act as resistance to water motions and affect lake hydrodynamics. Strong solar radiation and mild wind forcing typically occurring during the summer season result in weak stratification characterized by a diurnal cycle with a temperature differential of 1-3 • C. Temperature and circulation dynamics of a small and shallow lake are depicted by extensive field measurements and a three-dimensional non-hydrostatic model with a generic length scale (GLS) approach for the turbulence closure and drag forces induced by macrophytes. Results show that the effects of macrophytes on velocity profiles are apparent. In the pelagic area, the circulation patterns with and without macrophytes are similar. The velocity profile is generally characterized by a two-layer structure with the maximum velocity at both the water surface and the mid-depth. In contrast, inside the littoral zone, the mean flow is retarded by macrophytes and the velocity profile is changed to only one maximum velocity at the surface with a steeper decrease until 2.0 m depth and another slight decrease to the lake bottom. From the whole lake perspective, littoral macrophytes dampen the horizontal water temperature difference between the upwind side and download side of the lake. Macrophytes promote a stronger temperature stratification by retarding mean flows and reducing vertical mixing. Overall, this study shows that the temperature structures and circulation patterns under weak stratification conditions in a small and shallow lake are strongly affected by littoral vegetation.

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Section: Introductionmentioning

confidence: 99%

Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Torma

2019

Water

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“…The phasing of the flow response relative to the diurnal surface heat flux forcing will depend on the dynamic regimes for the buoyancy and cross-shore momentum balances (Farrow and Patterson 1993;Monismith et al 2006). Although the various mechanisms described above can provide intermittent perturbations to the thermally driven crossshore exchange, persistent forcing mechanisms, such as diurnal winds (Farrow 2013;Lin 2015) and tidally driven alongshore currents, can lead to systematic variability in the regular cross-shore exchange pattern.…”

Section: Introductionmentioning

confidence: 99%

Temporal Variability in Thermally Driven Cross-Shore Exchange: The Role of Semidiurnal Tides

Ulloa

Davis

Monismith

et al. 2018

Journal of Physical Oceanography

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We examine temporal variability of thermally driven baroclinic cross-shore exchange in the context of a tropical fringing reef system focusing on the role of tidally driven alongshore flow. Ensemble diurnal phase averaging of cross-shore flow at the Kilo Nalu Observatory (KNO) in Oahu, Hawaii, shows a robust diurnal signal associated with an unsteady buoyancy/diffusive dynamic balance, although significant variability is observed at subdiurnal time scales. In particular, persistent fortnightly variability in the cross-shore diurnal flow pattern is consistent with modulation by the semidiurnal alongshore tidal flow. The alongshore flow plays a direct role in the cross-shore exchange momentum balance via Coriolis acceleration but also affects the cross-shore circulation indirectly via its influence on vertical turbulent diffusion. An idealized linear theoretical model for thermally driven cross-shore flow is formulated using the long-term time-averaged diurnal dynamic balance at KNO as a baseline. The model is driven at leading order by the surface heat flux, with contributions from the alongshore flow and cross-shore wind appearing as linear perturbations. Superposition of the idealized solutions for Coriolis and time-varying eddy viscosity perturbations are able to reproduce key aspects of the fortnightly variability. Modifying the model to consider a more realistic alongshore flow and considering effects of nightly convection lead to further improvements in comparisons with KNO observations. The ability of the theoretical approach to reproduce the fortnightly patterns indicates that semidiurnal variations in the alongshore flow are effective in modulating the cross-shore flow via Coriolis and vertical turbulent transport mechanisms.

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“…For example, the non-linear effects, especially heat advection produced by a sharp change of vegetation distribution, are ignored. The effect of weak wind on thermal-induced circulation as [27] and [28] mentioned needs to be addressed in stratified environments. Also, the rooted emergent vegetation is assumed to have no effect on light extinction coefficients in the water body.…”

Section: Resultsmentioning

confidence: 99%

Effects of a sharp change of emergent vegetation distributions on thermally driven flow over a slope

Lin

2014

Environ Fluid Mech

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In this study, thermally driven flow within a sharp change of rooted emergent vegetation distributions is discussed. A conceptual and linear model is developed to study the interferences and competitions between two forcing mechanisms (vegetation shading and sloping bottom effects) on circulation patterns. The two forcing mechanisms can counteract or reinforce each other according to the presence of emergent vegetation in shallow or deep regions. For tall vegetation in shallows and open water in deep regions, vegetation shading leads to opposite temperature gradients against those from a slope. A critical vegetation blockage B critical is found to cause a minimum horizontal exchange flowrate and divide the flow regime as topographic or vegetation shading dominated. In clear water, opposite circulation from the bottom is produced and gradually spreads to the whole water column. On the contrary, in turbid water, the opposite circulation emerges from the water surface and gradually propagates to the sloping bottom. The circulation in turbid water is more easily affected by a sharp change of vegetation distributions rather than clear water. For open in shallows and tall vegetation in deep water, pressure gradients from vegetation shading can enhance buoyancy from the sloping bottom and lead to greater horizontal exchange flowrates. Due to a sharp change of emergent vegetation distributions, horizontal exchange flowrates are possibly increased and greater than those without vegetation. In short, circulation patterns and strength can be significantly affected by a sharp change of emergent vegetation distributions.

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Wind effect on diurnal thermally driven flow in vegetated nearshore of a lake

Cited by 10 publications

References 25 publications

Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Temporal Variability in Thermally Driven Cross-Shore Exchange: The Role of Semidiurnal Tides

Effects of a sharp change of emergent vegetation distributions on thermally driven flow over a slope

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