Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H30: Geophysical Fluid Dynamics: Air-Sea and Wave Interaction |
Hide Abstracts |
Sponsoring Units: DFD GPC Chair: Baylor Fox-Kemper, Brown University Room: 311 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H30.00001: Interactions of Ocean Fronts with Waves and Turbulence Baylor Fox-Kemper, Nobuhiro Suzuki High resolution simulations and observations of the ocean surface boundary layer have revealed 100m to 10km frontal and filamentary structures in temperature and other properties worldwide. The formation and evolution of these features, through frontogenesis, instability, and frontolysis is an important and often poorly-simulated part of the climate system, yet fronts and filaments strongly affect surface layer dynamics and the transport of energy, momentum, and gasses through this layer. These features also dominate the transport of oil spills and pollutants over a wide range of scales. Analysis of a multi-scale, non-hydrostatic, large eddy simulation spanning 20km fronts to 5m turbulence will be presented. The theory of the interactions of the fronts with turbulence and surface waves will be illustrated, and the consequences of these interactions on frontal strength and tracer transport will be quantified. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H30.00002: LES of Langmuir supercells under constant crosswind tidal forcing Rachel Walker, Jie Zhang, Mario Juha, Chester Gosch, Andres Tejada-Martinez We report on the impact of a crosswind tidal current on Langmuir supercells (LSCs) in shallow water computed via LES. LSCs consist of parallel counter rotating vortices engulfing the water column in unstratified conditions. These cells have been observed in shallow continental shelf regions of $\sim$15 meters depth during the passage of storms. The cells are aligned roughly in the wind direction and are generated by the interaction of the wind-driven shear current with the Stokes drift velocity induced by surface gravity waves. Without tides, LES reveals that the typical crosswind width of a LSC is $\sim$4 times the water column depth (H). Under a relatively weak crosswind tidal current (weaker than the downwind current), the constant crosswind tidal forcing applied causes a merging of cells leading to cells of width $\sim$8H. The opposite occurs under a crosswind tidal current stronger than the downwind current as the constant crosswind tidal force is able to break up the LSCs giving rise to smaller scale cells with different turbulent structure than that associated with LSC. Statistics of the turbulence during strong and weak crosswind tides will be contrasted and implications of an oscillating crosswind tidal force will be discussed. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H30.00003: Characteristics and Evolution of Passive Tracers in the Oceanic Mixed Layer Katherine Smith, Peter Hamlington, Baylor Fox-Kemper Ocean tracers such as CO$_2$ and plankton reside primarily in the mixed layer where air-sea gas exchange occurs and light is plentiful for photosynthesis. There can be substantial heterogeneity in the distributions of these tracers due to turbulent mixing, particularly in the submesoscale range where partly geostrophic eddies and small-scale 3D turbulence are both active. In this talk, LES spanning scales from 20km down to 5m are used to examine the role of turbulent mixing on nonreactive passive ocean tracers. The simulations include the effects of both wave-driven Langmuir turbulence and submesoscale eddies, and tracers with different initial and boundary conditions are examined. Tracer properties are characterized using spatial fields, statistics, multiscale fluxes, and spectra, and results show that passive tracer mixing depends on air-sea flux rate, release depth, and flow regime. The results indicate that while submesoscale eddies transport buoyancy upward to extract potential energy, the same is not true of passive tracers, whose entrainment is instead suppressed. Early in the evolution of some tracers, counter-gradient transport occurs co-located with regions of negative potential vorticity, suggesting that symmetric instabilities may act to oppose turbulent mixing. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H30.00004: Propagation of acoustic pulses in random gravity wave fields Christophe Millet, Alvaro de la Camara, François Lott A linear solution modeling the interaction between an incoming acoustic wave and a randomly perturbed atmosphere is developed, using the normal mode method. The wave mode structure is determined by a sound speed profile that is confining. The environmental uncertainty is described by a stochastic field obtained with a multiwave stochastic parameterization of gravity waves (GW). Using the propagating modes of the unperturbed atmosphere, the wave propagation problem is reduced to solving a system of ordinary differential equations. We focus on the asymptotic behavior of the transmitted waves in the weakly heterogeneous regime. In this regime, the coupling between the acoustic pulse and the randomly perturbed waveguides is weak and the propagation distance must be large enough for the wave to experience significant scattering. A general expression for the pressure far-field is derived in terms of saddle-point contributions. The saddle-points are obtained from a WKB approximation of the vertical eigenvalue problem. We present preliminary results that show how statistics of the transmitted signal are related to some eigenvalues and how an "optimal" GW field can trigger large deviations in the acoustic signals. The present model is used to explain the variability of infrasound signals. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H30.00005: On the relative contribution of inertia-gravity wave radiation to asymmetric instabilities in tropical cyclone-like vortices Konstantinos Menelaou, David A. Schecter, Peter M. K. Yau Intense geophysical vortices may experience various asymmetric instabilities during their life cycles. This study presents a method for evaluating the relative importance of different mechanisms that can simultaneously influence the growth of an asymmetric perturbation. The method is illustrated for vortices whose basic states are barotropic and have nonmonotonic radial distributions of potential vorticity (PV). A diagnostic formula for the growth rate of the perturbation is derived from an equation expressing conservation of angular pseudomomentum. In this formula, the growth rate is decomposed into several components relevant to the most unstable modes. One component accounts for the destabilizing interaction of phase-locked counter-propagating vortex Rossby (VR) waves. Other components account for inertia-gravity (IG) wave radiation and PV stirring in one or more critical layers. The dominant instabilities are examined in a parameter regime deemed relevant to tropical cyclone perturbations. As the Froude number increases from its lower bound, the main cause of instability typically transitions from VR-VR wave interaction (or critical layer stirring) to IG wave radiation. The transition can occur gradually or abruptly at a critical point for reasons that will be explained. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H30.00006: Wave modulation: the geometry, kinematics, and dynamics of surface-wave packets Nicholas Pizzo, W. Kendall Melville We derive moment evolution equations of the modified nonlinear Schrodinger equation (MNLSE) with application to interpreting the geometry, kinematics and dynamics of focusing deep-water wave packets. Our theory predicts modifications to the group velocity and associates wave packet convergence with the breakdown of equipartition between kinetic and potential energy. The evolution of the first moment of the energy density yields a natural way to interpret the concept of group velocity for these compact wave groups, predicting a velocity increase as the packet focuses, and is found to be up to 10\% larger than that predicted by linear theory, consistent with laboratory observations. The second moment yields a virial theorem, associating energy convergence with deviations from equipartition. The derivation of these moment equations relies crucially on the variational structure of the spatial version of the MNLSE, and the subsequent derivation of three conservations laws. These predictions are then examined numerically for focusing wave packets governed by both the MNLSE as well as the full potential flow equations, and the results are discussed in the context of existing theoretical, numerical and laboratory studies. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H30.00007: Jet drops from bursting bubbles: the importance of bubble shape in producing droplets James Bird, Peter Walls, Louis Henaux When wave-entrained bubbles rupture at the air-sea interface, the collapsing cavity produces a central jet that can eject droplets into the atmosphere. Previous experiments and theory predict that the production of these jet drops will be limited by either viscous or gravitational effects. Yet, little is understood about the limits of production when both gravitational and viscous effects are significant. Here, we conduct systematic experiments to explore the conditions necessary for jet drops to form. We propose that the role of gravity is most important before rupture, and carry out simulations that demonstrate the importance of the equilibrium bubble shape in the production of jet drops. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H30.00008: Air entrainment and bubble statistics in three-dimensional breaking waves Luc Deike, W.K. Melville, Stephane Popinet Wave breaking in the ocean is of fundamental importance in order to quantify wave dissipation and air-sea interaction, including gas and momentum exchange, and to improve parametrizationsfor weather and climate models. Here, we investigate air entrainment and bubble statistics in three-dimensional breaking waves through direct numerical simulations of the two-phase air-water flow using the Open Source solver Gerris [1]. As in previous 2D simulations[2], the dissipation due to breaking is found to be in good agreement with previous experimental observations and inertial-scaling arguments. For radii larger than the Hinze scale, the bubble size distribution, is found to follow a power law of the radius, r$^{\mathrm{-3}}$and to scale linearly with the time dependent turbulent dissipation rate during the active breaking stages. The time-averaged bubble size distribution is found to follow the same power law of the radius and to scale linearly with the wave dissipation rate per unit length of breaking crest. We propose a phenomenological turbulent bubble break-up model that describes the numerical results and existing experimental results. [1] Popinet, S. 2003. Journal of Computational Physics 190, 572--. Popinet, S. 2009. Journal of Computational Physics 228, 5838--. [2] Deike, L., Popinet, S., and Melville, W.K. 2015. Journal of Fluid Mechanics. vol 769, p541-569. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H30.00009: Simultaneous measurements of shape characteristics and radar backscattering of a water surface in a rain field Ren Liu, Xinan Liu, James H. Duncan The characteristics of radar backscattering from a water surface that is stimulated by a rain field are studied at laboratory scale. The experiment is carried out in a 1.22-m by 1.22-m water pool with a water depth of 0.3 m. Simulated raindrops are generated by an array of 22-gauge needles that are attached to the bottom of a water reservoir located above the pool. A two-dimensional horizontal translational motion is added to the water reservoir in order to vary the drop impact location for each needle during each experimental run. A cinematic Laser-Induced-Florescence (LIF) technique is used to measure the water surface shape while radar backscattering from the water surface is simultaneously recorded by a dual-polarized, ultra-wide band radar. Both the radar return intensity and the water surface shape are measured for a range of rain rates and a range of radar incidence angles. The relationship between the geometric features of the water surface shape and the radar return are explored. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H30.00010: Simulation-based study of air-sea momentum fluxes nearshore Xuanting Hao, Lian Shen Momentum fluxes at sea surface are crucial to air-sea interactions. In nearshore regions, the bathymetry variation has a significant impact on the surface wave field and complicates the momentum fluxes at water surface. In this study, we extend a high order spectral method to address wave-bottom interactions and wave modeling. From the wave simulation data, we use the Hilbert-Huang transform to quantify the properties of the wave spectrum, based on which the wave field is reconstructed for the detailed mechanistic study of wind-wave interactions using large-eddy simulation for the wind field. The roughness of the water surface is quantified using a dynamic model for the effects of subgrid-scale waves. The results show that the waves are sensitive to the water depth variation. Associated with the changes in the wave field, the momentum fluxes at the air-sea interface increase in shallow regions. [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