Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session U05: Geophysical Fluid Dynamics: Stratified Flows (8:45am  9:30am CST)Interactive On Demand

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U05.00001: Internal Wave Generation by Convection in a Sphere Daniel Lecoanet, Matteo Cantiello, Keaton Burns, Eliot Quataert, Louis Couston, Geoffrey Vasil, Benjamin Brown, Jeffrey Oishi When a stablystratified fluid layer lies adjacent to a convective fluid layer, the convection can excite internal gravity waves in the stablystratified fluid. Here we present a set of numerical simulations of wave generation by convection in spherical geometry using the Dedalus code. The convection is either driven by internal heating in the case of a full sphere (extending to r=0), or a bottom boundary condition in the case of a spherical shell. A piecewise linear equation of state causes a transition from a lower convective layer to an upper stablystratified layer. We calculate the frequency and wavenumberdependence of the excited waves as a function of the properties of the convection, the equation of state, and the geometry of the system. The waves are compared to waves generated by convection in cartesian geometry. [Preview Abstract] 

U05.00002: Downburst outflow with cooling source Yangyue Zhang, Ruifeng Hu, Xiaojing Zheng A downburst outflow can trigger thunderstorms or sandstorms. This work describes theories and direct numerical simulations that focus on the front velocity of gravity current produced by a downburst outflow with cooling source. A global theory based on the mass, momentum and energy conservations suggests that the front velocity and height are governed by the center height and longitudinal radius of the cooling source, while much less affected by the vertical radius.We also present a modified shallowwater theory allowing the longitudinal variation of depthaveraged temperature, which demonstrates that the longitudinal temperature gradient can also be a driving mechanism. Similarity solutions in conjunction with dimensional analysis predict various scaling laws during the inertial and viscous phases. In the inertial phase, cooling source can prevent the gravity current from slowing down, resulting in a steady propagating front. During the viscous phase, the decaying trend of front velocity is $t^{1/5}$, that is much gentler than $t^{4/5}$ in lockexchange flows. Twodimensional direction numerical simulations are conducted to justify the theoretical models, and good agreements with the theories are found. [Preview Abstract] 

U05.00003: Dynamics of continuously released gravity currents from a moving source Raphael Ouillon, Thomas Peacock, Eckart Meiburg Emerging technologies such as deepsea mining and geoengineering pose fundamentally new questions regarding the spatiotemporal dynamics of particledriven gravity currents. Such activities can continuously release dense sediment plumes which propagate as gravity currents along the sea bed. The study of gravity currents has historically focused on the dambreak configuration and a fundamental analysis of the flow resulting from the release of dense fluid from a moving source has never been carried out. Here, we present the results of idealized numerical simulations of this novel configuration, and investigate the propagation of the resulting gravity current as a function of the ratio of the source speed to the buoyancy velocity that results from the introduced density gradient. We show that above a certain value of this ratio, the flow enters a hyperbolic regime in which the source moves more rapidly than the generated current, resulting in a statistically steady state in the reference frame of the moving source. In this regime, fluid in the head of the current moves predominantly in the direction normal to the direction of motion of the source and the time evolution of the front is well described by the classical lockrelease mechanism. [Preview Abstract] 

U05.00004: Machine learning classification of stratified wakes using dynamic mode decomposition and decision trees Jonathan H. Tu, ChanYe Ohh, Geoffrey Spedding Previous work has shown that stratified wakes can be sorted into known regimes based on numerical criteria derived from the results of dynamic mode decomposition (DMD) [Ohh & Spedding, APS DFD 2019; OS19]. Here, we extend that work by applying methods from machine learning. As before, we compute features for each candidate wake using DMD: a dominant DMD mode is identified and characteristics of that mode, such as its symmetry in each crossstream direction, are computed. Those features are then used to train a decision tree classifier, which labels candidate wakes using a series of ifthen statements. This mirrors the general structure of the model developed previously in OS19, except that here, the criterion used for each ifthen statement is determined automatically by the decision tree training algorithm, rather than using human expertise. We find that our model is able to achieve high accuracy while maintaining interpretability, a common challenge in machine learning. Furthermore, the decision tree utilizes many of the same features that were chosen in OS19. [Preview Abstract] 

U05.00005: Quantifying mixing and available potential energy in vertically periodic simulations of stratified flows Christopher Howland, John Taylor, Colmcille Caulfield In a stably stratified Boussinesq fluid, irreversible diapycnal mixing describes the conversion of available potential energy (APE) to background potential energy (BPE). In some settings the APE framework is difficult to apply and approximate measures are used to estimate this mixing. For example, numerical simulations of stratified turbulence often use triply periodic domains to increase computational efficiency. In this setup however, BPE is not uniquely defined and the method of Winters et al. (1995, J. Fluid Mech., 289) cannot be directly applied to calculate the APE. We propose a new technique to calculate APE in periodic domains with a mean stratification. By defining a control volume bounded by surfaces of constant buoyancy, we can construct an appropriate background buoyancy profile $b_*(z,t)$ and accurately quantify diapycnal mixing in such systems. This new framework is consistent with the definition of a local APE density, useful for identifying mixing mechanisms. The evolution of APE is analysed in various turbulent stratified flow simulations. We show that the mean dissipation rate of buoyancy variance $\chi$ provides a good approximation to the mean diapycnal mixing rate, even in flows with significant variations in local stratification. [Preview Abstract] 

U05.00006: Erosion of a dense bottom layer by a gravity current Rui Zhu, Zhiguo He, Eckart Meiburg We investigate the erosion of a dense bottom layer by a gravity current, via NavierStokes Boussinesq simulations. The problem is governed by a dimensionless thickness parameter for the bottom layer, and by the ratio of two density differences. A quasisteady gravity current propagates along the interface and displaces some of the dense bottom fluid, which accumulates ahead of the gravity current and forms an undular bore or a series of internal gravity waves. Depending on the ratio of the gravity current front velocity to the linear shallowwater wave velocity, we observe smallamplitude waves or a train of steep, nonlinear internal waves. We develop a selfcontained model based on the conservation principles for mass and vorticity that does not require empirical closure assumptions. This model is able to predict the gravity current height and the internal wave or bore velocity, generally to within about 10{\%} accuracy. An energy budget analysis provides information on the rates at which potential energy is converted into kinetic energy and then dissipated, and on the processes by which energy is transferred from the gravity current fluid to the dense and ambient fluids. We observe that the energy content of thicker and denser bottom layers grows more rapidly. [Preview Abstract] 

U05.00007: Marangoni forces on oil droplets rising in a stratified fluid De Zhen Zhou, Adam Binswanger, Joshua Roe, Tracy Mandel, Maxime Thellard, Dustin Kleckner, Shilpa Khatri During the 2010 Deepwater Horizon oil spill, about 5 million barrels of petroleum discharged from the Macondo Well into the Gulf of Mexico. Oceanographic studies (McNutt, 2012) estimated that approximately 40 percent of that oil was trapped beneath the ocean surface, primarily in regions with strong oceanic density gradients. Previous numerical studies have shown that Marangoni forces may play a role in the trapping phenomenon (Blanchette, 2012). This work aims to verify the role and significance of interfacial surface tension effects of oil droplets rising through a sharply densitystratified fluid at intermediate Reynolds numbers. We will present experimental results comparing the motion of oil droplets rising through a sharp density stratification with varying Marangoni forces. [Preview Abstract] 

U05.00008: Tidal modulation of lee vortices in stratified flow past an isolated abyssal hill: a LES study Pranav Suresh Puthan, Geno Pawlak, Sutanu Sarkar A numerical study of flow past an idealized conical hill with height $h$ and bottom diameter $D$ is undertaken using the large eddy simulation (LES) technique. The abyssal flow is composed of two components: a uniform current ($U_c$) and an oscillatory tidal modulation ($U_t \sin(2\pi f_t t)$). A class of flows with strong stratification (Froude number, $Fr_c = U_c/Nh = 0.15 < O(1)$) and weak rotation (Rossby number, $Ro_c = U_c/2\pi f_i D = 5 > O(1)$) is examined. The wake shows cyclical shedding of coherent lee vortices and broadband turbulence. The velocity ratio ($U_t/U_c$) is fixed at unity and the ratio of natural shedding frequency $f_{s,c}$ in steady flow to the tidal frequency, $f^*=f_{s,c}/f_t$, is varied from 0.1 to 1. The flow exhibits different regimes, based on the presence or absence of synchronization of the vortex shedding from the body to the tidal forcing or its subharmonic. The control on the vorticity injected into the wake by tidal forcing is elaborated by examination of the temporal and spatial structure of the wake. [Preview Abstract] 

U05.00009: Stability analysis of resonant triads in a stably stratified uniform shear flow Lima Biswas, Priyanka Shukla We analyze the stability of resonant triads of internal waves in a twodimensional linearly stably stratified uniform shear flow, vertically confined between two parallel walls, by the amplitude equations for interacting waves. The interaction of two primary internal modes with the same frequency is considered, the superharmonic wave, generated by such interaction, is also an internal mode. For different buoyancy frequencies, we show the existence of triads formed by internal modes having the wave vector and frequency pairs as (\textbf{k}$_{\mathrm{\mathbf{m,}}}\omega )$, (\textbf{k}$_{\mathrm{\mathbf{n,}}}\omega )$ and (\textbf{k}$_{\mathrm{\mathbf{m}}} \quad +$\textbf{k}$_{\mathrm{\mathbf{n,}}}$2$\omega )$. The linear stability of resonant triads, around the exact equilibrium solution, is studied for various interactions. Triads containing the lowest mode number wave are linearly unstable. The exact solution of amplitude equations is presented under the pumpwave approximation, where the amplitude of one wave in a triad, namely, pumpwave, is larger than the amplitudes of other two waves. Neglecting the effect of two smaller waves on the pumpwave, we show that the triad is unstable when the wave with the lowest mode number acts as the pumpwave. [Preview Abstract] 

U05.00010: Numerical simulations of oil droplets rising in a sharply stratified fluid Adam Binswanger, De Zhen Zhou, Joshua Roe, Tracy Mandel, Dustin Kleckner, Maxime Theillard, Shilpa Khatri Rising droplets and bubbles in stratified fluids are a physical feature of many atmospheric and oceanic systems. For example, the Deepwater Horizon oil spill in 2010 resulted in large plumes of oil droplets being trapped as they rose in stratified layers in the Gulf of Mexico. To better understand how and why these plumes of oil droplets remained trapped, we produced high fidelity numerical simulations of a single oil droplet rising in a stratified flow, using a modified pressure correction projection method on adaptive nongraded octree grids and a coupled level setreference map method to capture the moving interface. These simulations are compared against recent experimental results, which characterized the velocity and dynamics of the retention of a droplet rising in stratification. Through simulations, we provide a detailed analysis of the forces acting on the droplet. [Preview Abstract] 

U05.00011: Internal Waves Scatter Energy into Interharmonics at the Critical Angle Bruce Rodenborn, Vrinda Desai, Yichen Guo, Michael Allshouse The reflection of internal wave beams from a solid boundary in a linearly stratified fluid has been studied theoretically (Kataoka and Akylas 2020) and experimentally (Rodenborn et al. 2011) to understand the partition of the reflected wave energy into propagating harmonic modes. Theory accurately predicts the dominant harmonic modes, but we use low Reynolds number experiments $(Re\sim 500)$, a 2D pseudospectral code and a 2D finite volume solver to show that the amount of energy after the wave beam reflects becomes vanishingly small when the boundary angle approaches the wave beam or the critical angle. We increase the Reynolds number to $Re\sim10^4$ in the simulations and find that at low boundary angles, most of the energy is transferred into the first harmonic wave. However, near the critical angle, reflection creates multiple waves at interharmonic frequencies so that the energy in harmonic modes is again very small, as we found at low $Re$. We attribute this energy loss in the primary modes to the growth of highly nonlinear processes in the reflection region as described by Korobov and Lamb (2008) in the case of internal wave generation. [Preview Abstract] 

U05.00012: Energy transfer in resonant and nearresonant internal wave triads for weakly nonuniform stratifications. Part I: Unbounded domain Anirban Guha, Saranraj Gururaj Using multiple scale analysis, reduced order equations for amplitude evolution is derived for resonant and nearresonant global triads consisting of weakly nonlinear internal gravity wave packets in weakly nonuniform density stratifications in an unbounded domain in the presence of viscous and rotational effects. Such triad interactions are one of the mechanisms by which internal waves cascades its energy to small scales, leading to ocean turbulence and mixing. Nonuniform stratification introduces detuning, i.e. mismatch in the vertical wavenumber triad condition, which may strongly affect the energy transfer process. We find that different triads undergo different amounts of detuning for the same changes in the background stratification. Additionally we study the effects of wavepackets' width, group speeds, nonlinear coupling coefficients, and viscosity on energy transfer and growth rates in weakly varying stratification. We also investigate the effect of detuning on energy transfer in varying stratification for different daughter wave combinations of a fixed parent wave. Moreover, we identify the optimal background stratification in a medium of varying stratification for a parent wave to form a resonant triad, which leads to maximal energy transfer. [Preview Abstract] 

U05.00013: Energy transfer in internal wave triads for nonuniform stratifications. Part II: Bounded domain with varying topography Saranraj Gururaj, Anirban Guha Weakly nonlinear triadic wavewave interactions is a mechanism by which energy from large scale oceanic internal waves cascades to small scales, finally leading to ocean mixing. Due to variations in submarine topography, ocean depth ($h$) is also variable, which in turn can impact the formation of resonant triads. Using multiple scale analysis, amplitude evolution equations of the waves forming a triad are derived in the presence of weakly varying $h$, assuming the waves slowly vary with amplitude but rapidly vary in phase both in space and time. For triads interacting in a medium of varying $h$ and uniform stratification, the horizontal wavenumber condition for waves (1,2,3), given by ${k}_{(1,a)}+{k}_{(2,b)}+{k}_{(3,c)}=0$ is unaffected, where $(a,b,c)$ are integers denoting the modenumber. For nonuniform stratification, triads (and selfinteractions) that do not satisfy the condition $a=b=c$ can violate the horizontal wavenumber condition as $h$ varies. In nonuniform stratification, the nonlinear coupling coefficients (NLC) do not decrease (increase) monotonically with increasing (decreasing) $h$. Also NLC may change by one order of magnitude with a slow change in $h$. Moreover, the most unstable triad was found to change with relatively small changes in $h$. [Preview Abstract] 

U05.00014: Turbulent mixing in a uniformly stratified shear layer at high Reynolds number Hieu Pham, Alexandra Vandine, Sutanu Sarkar Direct numerical simulations (DNS) are performed to investigate the dynamics of turbulent mixing in a shear layer with uniform stratification. The Reynolds number ($Re$) is large and the stratification is varied over a wide range of Richardson numbers ($Ri$). A myriad of secondary convective and shear instabilities develop on top of the primary KevinHelmholtz (KH) billows similar to what has been observed at high $Re$ in the oftenstudied case of shear between two constantdensity layers with different values of density. However, the mixing efficiency in the present study is considerably smaller and it remains relatively constant as the Richardson number approaches the viscous, finitedomain KH instability limit of Ri $\approx $ 0.18. After the turbulence has become fullydeveloped, the mixing efficiency peaks in the transition layers (which form at the edges of the shear layer) where the local shear and stratification are enhanced and evanescent internal waves are excited. Turbulence parametrization using buoyancy Reynolds number and bulk Richardson number shows a scaling that is more similar to what has been observed in homogenous stratified shear turbulence rather than in the twodensity shear layer. [Preview Abstract] 

U05.00015: Turbulent Mixing in a Linearly Stratified Shear Layer Sam Lewin, Colmcille Caulfield In order to develop a better understanding of the nature of ocean mixing, it is important to consider a variety of physical regimes that might represent different oceanic environments. Using high resolution direct numerical simulation at Reynolds number $Re=6000$, we investigate the dynamics and mixing properties of a shear flow embedded within a deep ambient density stratification (modeled as a linear background density profile) and compare our results to a flow with the widely studied hyperbolic tangent density profile that produces characteristic KelvinHelmholtz (KH) mixing. We observe that linearly stratified flows exhibit turbulence whose intensity may be strongly temporally intermittent, depending on the mechanisms by which the growing KH billows are destroyed. Nonmonotonic dependence of the irreversible mixing efficiency $\mathcal{E}$ (i.e. the ratio of the irreversible mixing rate to the sum of this rate and the kinetic energy dissipation rate) on the initial minimum Richardson number at the midpoint of the shear layer $Ri_m$ is observed, which may be used to improve existing mixing parameterisation schemes for largescale ocean models. [Preview Abstract] 

U05.00016: On The Structure And Characteristics Of Intermittent Patches In Stably Stratified Atmospheric Boundary Layers Abhishek Paraswarar Harikrishnan We investigate the Ekman flow simulations of Ansorge (2016) which describe the Atmospheric Boundary Layer (ABL) over a smooth orography with constant geostrophic forcing. Our database is comprised of three stratified cases at different stability regimes with the bulk Richardson numbers $Ri_{B} = 0.26, 0.58, 0.76$ and a neutrally stratified case. Following the ``Taxonomy of structures'' by Robinson (1991), we study the ABL in terms of its coherent structures with numerous scalar criteria. An appropriate threshold ($\tau_{p}$) is identified for each scalar criterion by determining the region of percolation transition. This transition can be seen when the threshold $\tau$ is continuously varied and the observed structure changes from being a complex connected cluster to simpler, disconnected clusters. Visualization at this threshold for a scalar criterion (say the $Q$criterion) reveals large regions devoid of structures for all stratified cases. This has been observed to extend from the outer layer to the viscous sublayer. We also extract individual structures at $\tau_{p}$ and geometrically characterize them with the help of three parameters namely the Shape Index, Curvedness and Stretching. Then, we proceed to compare their shapes for all cases. [Preview Abstract] 

U05.00017: Horizontal shear instabilities at low Prandtl number Pascale Garaud We present a first attempt at quantifying mixing by horizontal shear instabilities at low Prandtl number using Direct Numerical Simulations. This problem has many applications in stellar interiors, for instance. The shear in our model setup is driven by a body force, and rapidly becomes unstable. At saturation, we find several distinct dynamical regimes, depending on the relative importance of stratification and thermal diffusion. Based on our findings, we predict that shear in stars should fall into one of two categories: high P\'{e}clet number stratified turbulence, and low P\'{e}clet number stratified turbulence. The latter is presented in an accompanying talk by Cope, Garaud and Caulfield. Here, we focus on the case of high P\'{e}clet number (but low Prandtl number) stratified turbulence. We propose new theoreticallymotivated scaling laws for mixing in this regime, as well as a criterion to determine when this regime should be present. These compare well with our numerical experiments. [Preview Abstract] 

U05.00018: Buoyancydriven exchange flows in inclined ducts Adrien Lefauve, Paul Linden We tackle buoyancydriven exchange flows, which naturally occur whenever bodies of fluids at different densities are connected by a narrow constriction. To do so, we employ the canonical stratified inclined duct experiment, which sustains an exchange flow in an inclined duct of rectangular crosssection over long time periods. We present the first extensive, unified set of experimental data, in which the five nondimensional independent parameters of the experiment (the Reynolds number, tilt angle, duct aspect ratios, and Prandtl number) were systematically varied. This allowed us to make progress on the scaling laws of three dependent variables of particular interest: (i) the qualitative flow regime (laminar, wavy, intermittently turbulent, or fully turbulent), (ii) the mass flux (net transport of buoyancy between reservoirs), and (iii) the interfacial thickness (thickness of the layer of intermediate density between the two counter flowing layers). We also provide physical insight into these exchange flows, and explain some of their scaling laws by three classes of theoretical models: volumeaverage energetics, twolayer frictional hydraulics, and turbulent mixing. Finally we highlight areas in which future progress is needed. [Preview Abstract] 

U05.00019: The Dynamics of Stratified Horizontal Shear Flows at Low Péclet Number Laura Cope, Pascale Garaud, ColmCille Caulfield Stratified flows are ubiquitous; examples include atmospheres and oceans in geophysics and stellar interiors in astrophysics. The interaction of a stable stratification with a background velocity distribution can develop into stratified turbulence, key to transport processes in many systems. Geophysical flows, in which the Prandtl number $Pr \sim O(1)$, are often strongly stratified, nevertheless, turbulence still occurs. Density layering is key to understanding the properties of this ‘layered anisotropic stratified turbulence’ (LAST) regime that is characterised by anisotropic length scales and velocity fields. Conversely, $Pr \ll 1$ for astrophysical flows, inhibiting the formation of density layers. This suggests that LAST dynamics cannot occur, raising the question of whether analogous or fundamentally different regimes exist in the limit of strong thermal diffusion. This study addresses this question for the case of a vertically stratified, horizontallyforced Kolmogorov flow using a combination of linear stability theory and direct numerical simulations. Four distinct dynamical regimes emerge, depending upon the strength of the background stratification. By considering dominant balances in the governing equations, we derive scaling laws which explain the empirical data. [Preview Abstract] 

U05.00020: A coupled horizontal and vertical subgridscale dissipation scheme for atmosphere and ocean models Sina Khani, Michael L. Waite In atmosphere and ocean simulations with anisotropic horizontalvertical grids where $\Delta x \gg \Delta z$, subgridscale dissipation schemes are usually decoupled in the horizontal and vertical directions. In this framework, it is assumed that the energy exchange in the horizontal direction between unresolved horizontal scales and resolved scales, is totally decoupled from the energy exchange in the vertical direction between unresolved vertical scales and resolved scales. Using a careful and systematic horizontalfiltering and examination of subfilter terms in idealized stratified turbulence simulations, we show that the energy exchanges between resolved scales and unresolved horizontal and vertical scales are highly coupled. Indeed, having unresolved horizontal scales in the system implies a subgrid dissipation term in the vertical momentum equation. Our results show that with a coupled horizontalvertical subgrid dissipation scheme, the accuracy of results in the atmosphere and ocean models will be significantly enhanced at coarseresolution simulations. We will also discuss that how our new coupled subgrid dissipation scheme can be integrated into largescale climate models. [Preview Abstract] 

U05.00021: Automated stratified wake classification using Dynamic Mode Decomposition Chanye Ohh, Geoffrey Spedding There has been increasing interest in how and whether early wake information coming from body geometry and thrust ratios or acceleration parameters can persist into the late wake in a stratified fluid, because once formed, these late wakes have long persistence. At moderate values of the controlling parameters Re and Fr, stratified wakes are known to fall into a number of topologically distinct regimes, and these separable categories have been used to develop and test automated pattern detection algorithms, as reported in DFD19. Here, we report on continued work to improve the robustness of the automated wake classification. DMD modes of the flow are classified based on criteria set by the characteristics of each regime. The pattern classifier uses symmetry information about the wake centerline to determine the shape of the dominant mode, which is itself automatically selected according to a ranking by mode energy norm. The 3D wake data can be obtained both from tomographic PIV experiments, and from DNS for Re $\in$ [200, 1000] and Fr $\in$ [0.5, 8]. The identification process is further refined for spatially and temporally limited wake measurements. A collaboration with J. Tu (Carderock, DFD20) investigates an alternative datadriven approach using tools from machinelearning. [Preview Abstract] 
Not Participating 
U05.00022: A general criterion for the release of background potential energy through double diffusion Leo Middleton, John R. Taylor Double diffusion occurs when the fluid density depends on two components that diffuse at different rates (e.g. heat and salt in the ocean). Doublediffusive fluids display forms of convection not present in singlecomponent fluids as well as modifying the effects of canonical environmental flows (gravity currents, jets etc.). Energetically, double diffusion can lead to an upgradient buoyancy flux which may drive motion at the expense of potential energy. Here, we follow the work of Lorenz 1955 and Winters et al. 1995, for a singlecomponent fluid and define the background potential energy (BPE) as the energy associated with an adiabatically sorted density field and derive its budget for a doublediffusive fluid. We find that double diffusion can convert BPE into available potential energy (APE), unlike in a singlecomponent fluid, where the transfer of APE to BPE is irreversible. We also derive an evolution equation for the sorted buoyancy in a doublediffusive fluid, extending the work of Winters & D’Asaro 1996, and Nakamura 1996. The criterion we develop for a release of BPE can be used to analyse the energetics of mixing and double diffusion in the ocean and other multiplecomponent fluids. We illustrate its application using twodimensional simulations of salt fingering. [Preview Abstract] 

U05.00023: LES of a stratified reservoir subject to periodic wind stress and rotation Sara Markovi\'c, Vincenzo Armenio Lakes are often subject to periodic wind forcing in form of the surface shear stress. Energy induced by the wind is transferred to the internal waves and subsequently dissipated. A small portion of the introduced energy is spent on mixing, mainly near the boundaries. We are investigating how rotational effects influence the internal wave field and mixing that are excited by an oscillating surface shear stress. We conduct a series of numerical experiments on a laboratory scale where oscillating surface shear stress is applied to the rectangular basin of the stratified fluid in the rotating frame of reference. We focus on the Burger numbers that are relevant for the medium and smaller lakes. The simulations are carried out using Large Eddy Simulation. Three dimensional NavierStokes equations under the Boussinesq approximation for the density field are solved by the code that uses the OpenFOAM library. We focus on the midlatitudes, where layered stratification in lakes is common during summer. We have found that nearsurface mixing and boundary mixing are increased when rotational effects are introduced. Due to feedback that mixing may have on internal wave field, rotational effects can be important also for mediumsized lakes. [Preview Abstract] 

U05.00024: Abstract Withdrawn 
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