Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session A13: Geophysical: General I |
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Chair: Paul Linden, University of Cambridge Room: 27A |
Sunday, November 18, 2012 8:00AM - 8:13AM |
A13.00001: Numerical Simulation of the tidal effects on estuarine circulation in the San Juan Bay Edgardo Garcia, Miguel Canals, Jorge Capella, Julio Morell, Stefano Leonardi The regional oceanic modeling system ROMS has been implemented in San Juan Bay, Puerto Rico, to investigate quantitatively the mixing processes and as a forecast tool to support emergency planning and resource management in the area. The response of the San Juan Bay circulation to both river discharges and tidal forcing has been investigated. A hind-cast simulation is performed and compared with time series measurements and hidrographic data to validate the model. Sensitivity studies to turbulence mixing parameterization have been carried out under different forcing scenarios. A simulation without river outflow but forced with tidal constituents along the open boundaries is performed. Good agreement has been found with coastal observations with amplitudes gauges and modeled amplitudes constituents. A numerical experiment of the response of the Bay's circulation to river discharge only is performed and compared with the tide plus river forcing and tidal forcing only scenarios. Salinity distributions and vertical mixing are affected by the proximity to deep waters of the San Juan Bay Estuary, also the bulge region and plume structure in the entrance of San Juan Bay are highly affected by the bottom friction for the case with tide forcing. [Preview Abstract] |
Sunday, November 18, 2012 8:13AM - 8:26AM |
A13.00002: Cross-shore thermally-driven exchange on two coral reef shorelines Geno Pawlak, Lauren Tuthill, Wells Judith, Mark Merrifield, Stephen Monismith The dynamics of cross-shelf circulation influence the distribution of heat, salt, nutrients, contaminants, sediment, and planktonic organisms in the nearshore coastal ocean. For tropical reef coastlines, the horizontal redistribution of heat by cross-shelf circulation moderates the daily variations in temperature experienced by coral polyps, potentially reducing thermal stress. A key mechanism for this exchange is thermally driven baroclinic circulation. Here, observations from two reefs, at Eilat, Israel and Oahu, Hawaii, are presented that highlight the role of thermally forced exchange in cross-shore transport for distinct dynamic regimes. At each site, daytime conditions are characterized by offshore flow at the surface in response to increased temperatures in shallower water near shore. Nighttime cooling results in offshore flow near the bed. While an advection-dominated thermal balance provides a good description of the flows observed off Eilat by Monismith et al. (2006), phase differences between the heat flux, the thermal response and the cross-shore flows indicate that the Oahu flow is in an unsteady regime. Estimates of momentum and thermal balance terms from field data further confirm differences in flow regimes. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:39AM |
A13.00003: Wave, Current and Bottom Topographical Interactions in the Coastal Ocean Bottom Boundary Layer Aditya Nayak, Cheng Li, Daniel Choi, Joseph Katz PIV measurements were performed in the inner part of the coastal ocean bottom boundary layer (BBL), at a depth of 20m. 2D velocity distributions with resolution of 4.5 mm were obtained in two 28$\times $28 cm$^{2}$ planes, the first aligned with the current, and the second with the dominant wave direction. Filtering the reflection from the bottom facilitated velocity measurements starting from 3 mm above the seabed, fully resolving the inner part of the wave and current boundary layers. Co-located acoustic doppler velocimeter measurements were used to calculate Reynolds stress profiles by filtering out wave-induced motions from the PIV data. High-resolution sonar was used to map the bottom topography, and characterize the roughness. Several datasets, some spanning an entire tidal cycle were obtained at 6 Hz, under varying relative wave-current magnitude and directions, as well as ripple orientations. The PIV data resolved the interaction of currents and waves with the roughness, and suggested, consistent with the Grant and Madsen model, that the BBL contained two log layers with different slopes. The thicker and milder sloped log layer was part of the mean current boundary layer. Below it, a thinner layer with a higher slope was part of the wave boundary layer. [Preview Abstract] |
Sunday, November 18, 2012 8:39AM - 8:52AM |
A13.00004: Applications the Lagrangian description in aperiodic flows Carolina Mendoza, Ana Maria Mancho We use several recently developed Lagrangian tools for describing transport in general aperiodic flows. In our approach the first step is based in a Lagrangian descriptor (the so called function $M$). It measures the length of particle trajectories on the ocean surface over a given interval of time. We describe its output over satellite altimetry data on the Kuroshio current. The technique is combined with the direct computation of manifolds of Distinguished Hyperbolic trajectories and a very detailed description of transport is achieved across an eddy and a jet on the Kuroshio current [1,2]. A second velocity data set is examined with the M function tool. These are obtained from the HYCOM project on the Gulf of Mexico during the time of the oil-spill. We have identified underlying Lagrangian structures and dynamics. We acknowledge to the hospitality of the university of Delaware and the assistance of Bruce Lipphardt and Helga Huntley in accessing the model data sets. \\[4pt] [1] C. Mendoza, A.M. Mancho. Physical Review Letters 105 (2010), 3, 038501-1-038501-4.\\[0pt] [2] C. Mendoza, A.M. Mancho. The Lagrangian description of aperiodic flows: a case study of the Kuroshio Current. acepted in Nonlinear Proc. Geoph [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:05AM |
A13.00005: Formation and fate of contaminant particles controlled by turbulent coherent structures and geochemistry in a reactive river confluence Cristian Escauriaza, Christian Gonzalez, Paula Guerra, Pablo Pasten, Gonzalo Pizarro A river confluence in a 40-degree angle and with a high momentum ratio (M=12.8) generates the hydrodynamic mechanisms that control the formation and fate of arsenic-rich particles in an extremely arid region in northern Chile. Based on the conditions measured in the field, we carry out detached-eddy simulations (DES) and laboratory experiments for a simplified confluence, providing new insights on the effects of the streamwise helical vortices and recirculating regions on the turbulent mixing. A Lagrangian model is also developed to study the influence of large-scale coherent structures on particle transport, computing statistics of trajectories in the flow field and determining the characteristic time-scales of the flow. This investigation helps to clarify the complex interactions between the 3D vortical structures in the flow field and the geochemical reactions, which are the controlling mechanisms of particle formation and fate of the contaminants in the river. [Preview Abstract] |
Sunday, November 18, 2012 9:05AM - 9:18AM |
A13.00006: Water-wave diffraction by small undulation on a porous ocean-bed in the presence of surface tension in a two-layer fluid Subash Chandra Martha, Srikumar Panda The problem involving wave scattering in a two-layer fluid due to small bottom undulation on the porous ocean-bed is investigated within the framework of two-dimensional linearized water wave theory in the presence of surface tension at the upper free surface. In each layer it is assumed that the flow is irrotational and the fluid is inviscid and incompressible. In such a two-layer fluid there exist waves with two different modes, one with lower wave number propagate in the upper layer whilst those with higher wave number propagate in the lower layer. An incident wave of a particular mode gets reflected and transmitted by the undulating bottom into waves of both modes. By employing perturbation analysis in conjunction with Fourier transform method, the governing BVPs are solved and the reflection and transmission coefficients are obtained in terms of integrals involving the shape function $c(x)$ representing the bottom undulation. These coefficients can be evaluated once the shape function is known. One special type of undulating bottom is considered as an example to evaluate the related coefficients in detail. These coefficients are depicted graphically to demonstrate the transformation of energy between the two different modes and also to validate the theoretical observations. [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:31AM |
A13.00007: Gravity currents in strongly stratified fluids Benjamin Maurer, Paul Linden For fluids subject to gravity, vertical density gradients are stable while horizontal density gradients often sharpen to laterally propagating fronts called gravity currents. As recent studies have shown, the energetics and therefore the dynamics of gravity currents propagating in a stratified fluid are affected by the vertical density stratification. To investigate the role of vertical stratification in the flow dynamics, we conducted an experimental and numerical study of buoyancy-driven, high \textit{Re }lock-releases between two fluids of equal density stratification structure and strength but differing depth-averaged densities. We examined both layered and continuous vertical density stratifications, focusing on the cases where the vertical density gradients are strong relative to the horizontal mean density difference. Lock-releases between discretely layered fluids of unequal depth-averaged densities result in multiple interleaving flows advected by a less energetic full-depth flow. Lock-releases between linearly stratified fluids of unequal depth-averaged densities result in a full-depth flow similar to the less energetic flow in the discretely layered case. We present dimensional analysis and energy scaling models describing the relevant length scales and buoyancy forcing [Preview Abstract] |
Sunday, November 18, 2012 9:31AM - 9:44AM |
A13.00008: A radar backscattering mechanism of ocean surface in response to rainfall Xinan Liu, Quanan Zheng, Ren Liu, James H. Duncan The characteristics of ocean surface in response to rainfall and its radar back-scatter are simultaneously measured in laboratory. The experiment is carried out in a water pool that is 1.22~m by 1.22~m with a water depth of 0.3~m. Artificial rainfall is generated from an array of hypodermic needles. The surface characteristics including crowns, stalks, secondary droplets and ring waves are measured with a cinematic Laser-Induced-Florescence (LIF) technique. Our experimental results show that impinging raindrops on the water surface generate various water surface structures with different relative sizes. Among them stalks and crowns comprise the dominant radar backscattering. On the basis of these laboratory experiments and theories of radar scattering from a rough surface, a near-resonance radar backscattering model for quantifying the dependence of the radar return intensity on rain rate on the ocean surface is developed. The model explains the radar response to rain rate simultaneously observed by C-band ASAR and ground-based weather radar. The physical model provides reasonable mechanisms to explain the frequency dependence and polarization behavior of radar signatures from rain cells on the ocean surface. [Preview Abstract] |
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