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 L1: Geophysical: Oceanographic VI |
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Chair: Patrice Le Gal, Aix Marseille University Room: 323 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L1.00001: Breaking of the internal tide Karl Helfrich, Roger Grimshaw, Edward Johnson Nonlinear steepening of low-mode internal tides and the subsequent arrest of steepening by non-hydrostatic dispersion is a common mechanism for the generation of internal solitary waves in the ocean. However, it is known that the earth's rotation may interfere and prevent the emergence of the solitary waves. The Ostrovsky equation, the Korteweg-de Vries equation with a nonlocal integral term representing the effects of rotation, is introduced as model for these processes. Recent work on a breaking criteria for the reduced Ostrovsky equation (in which the linear non-hydrostatic dispersive term with a third-order derivative is eliminated) is discussed. This equation is integrable provided a certain curvature constraint is satisfied. It is demonstrated, through theoretical analysis and numerical simulations, that when this curvature constraint is not satisfied at the initial time, then wave breaking inevitably occurs. The breaking criteria is applied to several oceanic examples including internal tides in the South China Sea and radiation of the internal tide from the Hawaiian Island chain. [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L1.00002: From weak to strong turbulence: a traveling wave tour Francesco Fedele The weak wave turbulence of Zakharov unveiled the dynamics of ocean waves as that of a sea of nonlinearly interacting dispersive elementary waves. Their dispersive properties and energy cascade can be observed and measured in the ocean. In this regard, I will discuss recent experiments off the Venice coast that exploit a Variational Wave Acquisition Stereo System (VWASS) to study the space-time dynamics of sea waves [Fedele et al. 2013, Ocean Modeling]. The delicate balance of dispersion and nonlinearities may yield the formation of solitons or traveling waves [Fedele {\&} Dutykh 2012, JFM 712:646]. These are introduced in the context of the Euler equations and the associated third order compact Zakharov equation. Traveling waves exist also in the strong turbulence of the Navier-Stokes (NS) equations. Indeed, for bounded geometries I will show that the NS equations can be reduced to generalized Camassa-Holm equations [Fedele 2012, Fluid Dyn. Res. 44:045509; Fedele {\&} Dutykh 2013, EPL 101:34003]. From a dynamical system perspective, in phase space the associated vector field supports an invariant group orbit manifold, which corresponds in physical space to smooth and singular axisymmetric vortexons [5]. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L1.00003: Large overturns at a model Luzon Strait topography: an application of the Immersed Boundary Method Narsimha Rapaka, Sutanu Sarkar An Immersed Boundary Method (IBM) is used to study the internal wave field in a model of the Luzon Strait topography, a double ridge system with different heights and local roughness. Scale compression is employed, leading to horizontal scales of O (100 m) instead of km. Strong internal tide beams are generated on both the east and the west ridges near the critical regions where the internal wave characteristic slope matches with that of the topographic slope. A large fraction of the radiated tidal energy is confined near the top surface owing to ducting by the pycnocline. Isopycnal displacement is particularly large (around 200 m after scaling up) at the eastern flank of the west ridge, which corresponds to the station N2 of Alford et al., 2011 (JPO). The wave displacements at the east ridge is influenced by the proximity of the pycnocline. The spatial distribution of baroclinic energy conversion and internal wave flux is assessed. [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L1.00004: Response of Ocean Circulation to Different Wind Forcing in Puerto Rico and US Virgin Islands Miguel Solano, Edgardo Garcia, Stafano Leonardi, Miguel Canals, Jorge Capella The response of the ocean circulation to various wind forcing products has been studied using the Regional Ocean Modeling System. The computational domain includes the main islands of Puerto Rico, Saint John and Saint Thomas, located on the continental shelf dividing the Caribbean Sea and the Atlantic Ocean. Data for wind forcing is provided by an anemometer located in a moored buoy, the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) model and the National Digital Forecast Database (NDFD). Hindcast simulations have been validated using hydrographic data at different locations in the area of study. Three cases are compared to quantify the impact of high resolution wind forcing on the ocean circulation and the vertical structure of salinity, temperature and velocity. In the first case a constant wind velocity field is used to force the model as measured by an anemometer on top of a buoy. In the second case, a forcing field provided by the Navy's COAMPS model is used and in the third case, winds are taken from NDFD in collaboration with the National Centers for Environmental Prediction. Validated results of ocean currents against data from Acoustic Doppler Current Profilers at different locations show better agreement using high resolution wind data as expected. [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L1.00005: Relation of Lagragian structures and drifter dynamics in the Gulf of Mexico Carolina Mendoza, Ana Maria Mancho, Stephen Wiggins We use a Lagrangian descriptor (the so called function $M$) which measures the length of particle trajectories on the ocean surface over a given interval of time [1,2,3]. With this tool we identify the Lagrangian skeleton of the flow and compare it on three datasets over the Gulf of Mexico during the year 2010. The satellite altimetry data used come from AVISO and simulations from HYCOM GOMl0.04 experiments 30.1 and 31.0. We contrast the Lagrangian structure and transport using the evolution of several surface drifters. We show that the agreement in relevant cases between Lagrangian structures and dynamics of drifters depends on the quality of the data on the studied area. \\[4pt] [1] C. Mendoza, A.M. Mancho. Phys. Rev. Lett. 105 (2010), 3, 038501.\\[0pt] [2] C. Mendoza, A.M. Mancho. Nonlin. Proc. Geophys. 19 (4) (2012) 449-472.\\[0pt] [3] A.M. Mancho, S. Wiggins, J. Curbelo, C. Mendoza. Commun. Nonlinear. Sci. Numer. Simul. 18 (2013) 3530-3557. [Preview Abstract] |
Monday, November 25, 2013 4:40PM - 4:53PM |
L1.00006: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 4:53PM - 5:06PM |
L1.00007: Laboratory experiments investigating the influence of subglacial discharge on submarine melting of Greenland's Glaciers Claudia Cenedese A set of idealized laboratory experiments investigates the ice-ocean boundary dynamics near a vertical ``glacier'' (i.e. no floating ice tongue) in a two-layer stratified fluid, similar to Sermilik Fjord where Helheim Glacier terminates. In summer, the discharge of surface runoff at the base of the glacier (subglacial discharge) causes the circulation near the glacier to be much more vigorous and is associated with a larger melt rate than in winter. In the laboratory the effect of a subglacial discharge is simulated by introducing fresh water at melting temperatures from a source at the base of the ice block representing the glacier. The influence of both a line and a point source of subglacial discharge on submarine melting are investigated. A buoyant plume of cold melt water and subglacial discharge water entrains ambient waters and rises vertically until it finds either the interface between the two layers or the free surface. The results suggest that the melt water deposits within the interior of the water column and not entirely at the free surface, as confirmed by field observations and numerical experiments. Furthermore, the submarine melting increases with subglacial discharge. Finally, a non-monotonic dependence of the submarine melting on the distance between two point sources of subglacial discharge suggests that the distribution and number of sources of subglacial discharge may play an important role in glacial melt rates. [Preview Abstract] |
Monday, November 25, 2013 5:06PM - 5:19PM |
L1.00008: Upstream versus downstream control of meltwater plumes under ice shelves Andrew Wells In many locations the Greenland and Antarctic ice sheets discharge into the ocean through ice shelves floating on top of a warm salty ocean. The turbulent buoyancy-driven flow of meltwater beneath the sloping ice-shelf base enhances heat transfer and provides a feedback on ice melting rates, with consequences for ice sheet dynamics and predictions of sea-level rise. Previous steady-state models of meltwater plumes under ice shelves have solved for the development of flow along the slope from an initial source, corresponding to solely upstream control of the plume dynamics. I re-interpret the plume dynamics embedded within the framework of a time-dependent model, and show that the flow exhibits distinct regimes depending on the source conditions. Solutions with upstream control are physically consistent for certain source conditions, but the plume is influenced by a combination of upstream and downstream conditions in other regions of parameter space. The dynamics are illustrated for flow underneath a two-dimensional ice shelf of initially constant basal slope, and stable attracting states are determined. The implications for modelling meltwater flow under ice shelves are discussed. [Preview Abstract] |
Monday, November 25, 2013 5:19PM - 5:32PM |
L1.00009: Turbulent mixing in a barrier layer Hieu Pham, Sutanu Sarkar Large-eddy simulation (LES) is used to investigate the erosion of a barrier layer in the upper ocean by wind-driven turbulence. The initial vertical density profile consists of three regions: a buoyantly neutral surface layer, an isothermal salt-stratified region (the so-called barrier layer) and a thermally stratified deep region. A constant wind-stress and a diurnal heat flux are applied at the surface to drive the turbulence. During the night, the wind stress generates shear in the mixed layer. The shear deepens and causes Holmboe shear instability at the interface between the mixed layer and the barrier layer where the gradient Richardson number falls below 0.25. In time, the barrier layer becomes thinner, and the mixed layer thickens with increasing surface salinity. In the morning, as the surface heat flux warms the mixed layer, a temperature inversion is formed on top of the barrier layer. The surface heating suppresses the turbulence in the surface layer; however, the mean shear continues to increase and causes occasional bursts of shear instability. The instability mixes up the temperature inversion by the afternoon. [Preview Abstract] |
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