Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session A36: Geophysical: Oceanographic I |
Hide Abstracts |
Chair: Peter Diamessis, Cornell University Room: 407 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A36.00001: Modifications to Symmetric and Baroclinic Instabilities in the Presence of Surface Gravity Waves Sean Haney, Baylor Fox-Kemper, Keith Julien The depth of the ocean mixed layer is determined by several processes that mix and restratify the ocean. The classical Eady problem (linear stability of flow in thermal wind balance) describes the growth of baroclinic instabilities which are important for restratification in the mixed layer. The Eady problem has been extended by Stone to include non-hydrostatic effects and a range of Richardson numbers appropriate for the ocean mixed layer. Here, the problem is extended further to include the Stokes drift (a drift current that is the time averaged effect of the surface gravity waves). A new, wave-induced, instability is introduced that coexists with the symmetric and baroclinic instabilities. In addition, both the symmetric and baroclinic instabilities are modified by the presence of Stokes drift. While the baroclinic mode becomes a hybrid baroclinic/wave-induced mode at modest wave forcing, the symmetric mode is only slightly modified. This transition to a hybrid mode is marked by a change in the energy source and the vertical structure. Dominance by each of the three modes may occur in a realistic parameter regime for the ocean mixed layer, and therefore wave forcing cannot be neglected when considering the stability of the mixed layer. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A36.00002: Sea-surface manifestation of a submerged stratified turbulent wake via wake-emitted internal gravity waves Qi Zhou, Peter Diamessis A submerged turbulent wake in the stratified ocean may become visible at the sea surface due to the internal gravity waves (IGWs) which are emitted by the wake and propagate towards the surface. In a linearly stratified Boussinesq fluid, we examine such a wake and wake-emitted IGWs at wake Reynolds number $Re \in[5\times10^{3},10^{5}]$ and Froude number $Fr \in[4,16,64]$ using three-dimensional implicit Large Eddy Simulations. A spectral multidomain penalty scheme in the vertical enables finer resolution of both the IGW-emitting wake and the subsurface region where the IGWs interact with a free-slip sea surface. At various wake parameters, including $Re$, $Fr$ and the evolution stage of a wake, we report the length- and time-scales of reflecting IGWs at the surface, statistics of magnitudes and orientations of IGW-induced surface strains, and mean momentum fluxes due to IGWs. A case study concerning the visibility of the surfacing IGWs from remote sensors is performed by considering possible local enrichment of surfactant due to the surface IGW currents/strains. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A36.00003: The surface generation and downward propagation of internal waves in nonlinear stratifications Sasan Ghaemsaidi, Thomas Peacock, Thierry Dauxois, Sylvain Joubaud, Philippe Odier An important topic in physical oceanography is the generation of internal waves by surface forcing, and the subsequent propagation of these waves into the deep ocean, often through complex density stratifications. This scenario is of particular interest in the Arctic Ocean, where increased summer ice loss is leading to enhanced internal wave activity, which in turn impacts circulation via wave breaking and mixing. We present the results of a combined theoretical and laboratory experimental study of this scenario, seeking to identify key parameters that significantly influence the amplitude of the wave field transmitted to the deep ocean. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A36.00004: Characterization of the Vertical Energy Distribution of the Internal Wave Field in the Upper Ocean Jeremy Bruch A method to simulate internal waves in the upper ocean is proposed by defining the vertical energy distribution as a function of mode number with the associated vertical structure functions as an appropriate set of orthogonal basis functions. An internal wave simulation is shown for a case with a stylized BV peak profile, using the Garrett and Munk internal wave model (GM) as the input energy distribution. The resulting simulated spectra are shown to be self-consistent with the proposed definition of the vertical energy distribution. Application of the GM model requires many assumptions, including the requirement that the internal waves are modeled strictly in deep water where there is little variation in the stratification. Given the typical non-uniformity of the stratification profile in the upper ocean, it may be of interest to relax this restriction of the GM model but the obvious non-stationary properties near the thermocline are incompatible with the calculation of the vertical spectrum of the internal wave field. The method described in this presentation suggests a means to reconcile this incompatibility. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A36.00005: Internal Solitary Wave Tunnelling Bruce Sutherland, Scott Keating, Ishita Shrivistava In a two-layer fluid, solitary waves of depression (elevation) propagate in a shallow upper (lower) layer. The transition from depressed to elevated is known to occur as a solitary wave of depression passes over a bottom slope. If impacting a coastline the shoaling waves deposit some energy and partially reflect. Here we consider what happens if a solitary wave passes over a sill or the shoulder of an island. Specifically, through lock-release laboratory experiments, we examine the evolution of a solitary wave of depression incident upon a submerged thin vertical barrier and triangular submarine topography. From the measured interface displacement, we determine the available potential energy associated with the wave. The method of Hilbert transforms is used to subdivide the displacement signal into rightward- and leftward-propagating disturbances, from which we measure the available potential energy of the transmitted and reflected waves. These are used to measure the relative transmission, reflection and deposition of energy in terms of the barrier height and slope, the relative depths of the ambient fluid and the amplitude of the incident wave. Implications for internal wave scattering around Dongsha Atoll in the South China Sea are discussed. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A36.00006: Mass transport by large and very-large amplitude mode-2 internal solitary waves: experimental observations Kara Shipley, Alan Brandt The present experiments provide the first quantitative measurements of the mass transport by mode-2 internal solitary waves (ISW) propagating on a thin pycnocline. The ISW were generated by the release of fluid from an initially mixed volume. It was found that the amplitude and amount of mass transported by the leading and second, following ISW was proportional to the level of forcing and was attenuated at an approximately uniform rate as the ISW propagated downstream. At the highest level of ISW forcing, over 40\% of the mixed fluid was transported within the leading ISW. Excellent agreement was found with the numerical simulations of Salloum et al. (2012) that were designed to replicate the present experimental configuration. In addition, a new ISW regime was identified, termed very large-amplitude ISW, where the ISW bulge wavelength and extent of mass transported increased with amplitude at a rate greater than the lesser amplitude ISW. In recent years the frequent occurrence of large amplitude ISW in the coastal ocean has been observed. The present experiments and the associated numerical simulations can provide insight into the effects of ISW transport on coastal mixing and biological material distribution. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A36.00007: Simultaneous experimental measurements of velocity and density in solitary internal waves with trapped cores P. Luzzatto-Fegiz, K. Helfrich Long internal waves with trapped cores are relatively common in the ocean and atmosphere (e.g. Lien et al. 2012). It has been proposed that such waves may be important for transporting mass, energy, and biological matter across the continental shelf (Shroyer et al. 2010, Scotti \& Pineda 2004). However, several fundamental wave properties, including mass and energy transport, as well as core circulation and density structure, remain to be quantified experimentally. A key prerequisite, for such measurements, involves simultaneously accessing the velocity and density fields with sufficient resolution. We employ a setup comprising a thin linearly stratified region overlaying a deep, uniform-density layer, and perform experiments with and without a no-slip lid at the surface. The waves are produced by a lock-release mechanism. We develop a technique for high-resolution, simultaneous measurements of velocity and density in stratified flows, using pulsed-laser, co-planar PIV and LIF. We are thereby able to extract properties including phase velocity, kinetic and potential energies, minimum Richardson number, as well as core size, circulation and density. To examine larger waves, we complement these results with numerical simulations, which are in good agreement with our experiments. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A36.00008: Effect of External Turbulence on the Evolution of a Towed Wake in a Stratified Environment Anikesh Pal, Sutanu Sarkar Direct numerical simulation (DNS) is used to study the effect of external turbulence on the evolution of a towed turbulent wake in a stratified fluid. The simulations are carried out at a Reynolds number of 10,000, Froude number of 3 and Prandtl number of 1. The external turbulence is generated from a triply periodic rectangular domain in an auxiliary simulation performed to obtain turbulence with desired ${u^{'}_{ext}}/{U_0}$, where $u^{'}_{ext}$ is the root mean square velocity of the external turbulence and $U_0$ is the maximum defect velocity of the pure towed wake. This field of external turbulence is added to the initial field of the towed turbulent wake. Simulations are performed for ${u^{'}_{ext}}/{U_0} = 0.10, 0.20$ and $0.30$. The kinetic energy of the towed wake decays faster with progressively increasing values of ${u^{'}_{ext}}/{U_0}$. This effect of external turbulence is found to be stronger in stratified flow relative to the neutral case. Although the horizontal spread of the stratified wake is enhanced owing to external turbulence there is little effect on the vertical spread. [Preview Abstract] |
Sunday, November 24, 2013 9:44AM - 9:57AM |
A36.00009: Drag Coefficients of Drifting Waterbirds Karl von Ellenrieder, Kevin Kenow, Huajin (Ariel) Qu, Tsung-Chow (Joe) Su A series of towing tank experiments has been performed to support the development of a probabilistic source tracking model that can be used to estimate the origin of waterbird die-offs. While monitoring the appearance of waterbird carcasses on beaches provides the primary means of assessing the magnitude, as well as the spatial and temporal patterns of die-offs, interpreting the actual site of exposure to toxins is hampered by a lack of information on the drift patterns of carcasses and the confounding influences of wind/current. In this work, a series of experimental measurements were conducted on Common Loon and Lesser Scaup carcasses to obtain steady drag coefficients of representative waterbird species. The tests were designed to capture the drag coefficients associated with current speeds of between 0.2 and 0.8 meters per second and wind speeds of up to 10 meters per second at different levels of carcass submergence. Using the submerged frontal area of an ellipse, together with the frontal area of any submerged portions of the head and neck gives good similarity across the ranges of speeds and submergence levels tested. An example approach to determining waterbird drift velocity and direction from knowledge of the drag coefficients, wind and current is provided. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700