Critical effects of a tall seamount on a drifting vortex

The initial-value problem for the evolution of an isolated vortex encountering a tall seamount during its westward beta-drift is studied within an equivalent-barotropic model, that is generalized to allow for the intersection of the layer interface with a sloping bottom. Given the Rossby radius and linear wave speed in the model, the parabolic shape of a seamount top and initial potential vorticity profile in the vortex core, the outcome is controlled by the vortex sign and a number of parameters: the seamount radius and height of penetration into the active layer, the radius and intensity of the vortex, the initial offset of the vortex center relative to the seamount, the Ekman layer depth over the seamount top, and the momentum lateral diffusion coefficient. Here we consider regimes for narrow seamounts where cyclonic vorticity generated in the water column swept off the top of the seamount plays a negligible role. The most significant effect on the vortex evolution is provided by a topographically induced anti-cyclonic circulation that is formed after squashing of water column replaced over the top of the seamount by the approaching vortex. The Geostrophic Vorticity intermediate model is used for numerical experiments. When the area of penetration is small and the topographic anticyclone is weak, the vortex drifts either predominantly westward north of the seamount or rotates around the seamount which is explained by presence of a separatrix in a simple kinematic model. For a larger area of penetration and stronger topographic anticyclone, violent interactions result in substantial deformations of the vortex core and loss of the material from the vortex periphery that leads to anomalous transport and diffusion. Vortex capture over the seamount is found in one range of parameters

Stabilization of Isolated Vortices in a Rotating Stratified Fluid

The key element of Geophysical Fluid Dynamics—reorganization of potential vorticity (PV) by nonlinear processes—is studied numerically for isolated vortices in a uniform environment. Many theoretical studies and laboratory experiments suggest that axisymmetric vortices with a Gaussian shape are not able to remain circular owing to the growth of small perturbations in the typical parameter range of abundant long-lived vortices. An example of vortex destabilization and the eventual formation of more intense self-propagating structures is presented using a 3D rotating stratified Boussinesq numerical model. The peak vorticity growth found during the stages of strong elongation and fragmentation is related to the transfer of available potential energy into kinetic energy of vortices. In order to develop a theoretical model of a stable circular vortex with a small Burger number compatible with observations, we suggest a simple stabilizing procedure involving the modification of peripheral PV gradients. The results have important implications for better understanding of real-ocean eddies

Modeling of composite beams and plates for static and dynamic analysis

The main purpose of this research was to develop a rigorous theory and corresponding computational algorithms for through-the-thickness analysis of composite plates. This type of analysis is needed in order to find the elastic stiffness constants for a plate and to post-process the resulting plate solution in order to find approximate three-dimensional displacement, strain, and stress distributions throughout the plate. This also requires the development of finite deformation plate equations which are compatible with the through-the-thickness analyses. After about one year's work, we settled on the variational-asymptotical method (VAM) as a suitable framework in which to solve these types of problems. VAM was applied to laminated plates with constant thickness in the work of Atilgan and Hodges. The corresponding geometrically nonlinear global deformation analysis of plates was developed by Hodges, Atilgan, and Danielson. A different application of VAM, along with numerical results, was obtained by Hodges, Lee, and Atilgan. An expanded version of this last paper was submitted for publication in the AIAA Journal

Test of Einstein Equivalence Principle for 0-spin and half-integer-spin atoms: Search for spin-gravity coupling effects

We report on a conceptually new test of the equivalence principle performed by measuring the acceleration in Earth's gravity field of two isotopes of strontium atoms, namely, the bosonic $^{88}$Sr isotope which has no spin vs the fermionic $^{87}$Sr isotope which has a half-integer spin. The effect of gravity upon the two atomic species has been probed by means of a precision differential measurement of the Bloch frequency for the two atomic matter waves in a vertical optical lattice. We obtain the values $\eta = (0.2\pm 1.6)\times10^{-7}$ for the E\"otv\"os parameter and $k=(0.5\pm1.1)\times10^{-7}$ for the coupling between nuclear spin and gravity. This is the first reported experimental test of the equivalence principle for bosonic and fermionic particles and opens a new way to the search for the predicted spin-gravity coupling effects.Comment: 5 pages, 4 figures. New spin-gravtity coupling analysis on the data added to the manuscrip

Transformation of an Agulhas eddy near the continental slope

The transformation of Agulhas eddies near the continental slope of southern Africa and their subsequent self-propagation are analyzed in both observational data and numerical simulations. Self-propagation results from a net dipole moment of a generalized heton structure consisting of a surface-intensified anticyclonic eddy and deep cyclonic pattern. Such Agulhas vortical structures can form near the retroflection region and further north along the western coast of southern Africa. We analyze nonlinear topographic wave generation, vortex deformations, and filament production as an important part in water mass exchange. Self-propagating structures provide a conduit for exchange between the deeNational Science Foundation (U.S.) (Grant OCE-0752346

Deep cyclogenesis by synoptic eddies interacting with a seamount

Strong deep eddies with cyclonic vorticity greater than 0.2 f0 were detected using an array of bottom current and pressure measurements in the Kuroshio Extension System Study (KESS) in 2004–2006. Daily maps showed these deep eddies developed locally. As in the Gulf Stream, meandering of the upper baroclinic jet generates deep cyclones and anticyclones by stretching and squashing the lower water column. However, unlike the Gulf Stream, the smaller vertical stretching and greater water depth in the Kuroshio Extension limits the relative vorticity generated by this vertical coupling process to about 0.1 f0. In the deep Kuroshio Extension the strong cases of vorticity generation and cyclone development are related to stretching driven when water columns are advected off isolated seamounts in the region. The large observed values of relative vorticity are consistent with a straightforward calculation of deep layer potential vorticity conservation.A barotropic model is used to illustrate the topographic generation of cyclones by ambient currents in synoptic eddies. Positive potential vorticity filaments also develop during the cyclogenetic process with width LR = O(20 km), where LR is the topographic Rhines scale, and travel anticyclonically around the seamount. Observational evidence lends support to the existence of submesoscale filaments, insomuch as current meter records near the flanks of seamounts exhibited bursts of eddy kinetic energy when bandpass-filtered between the inertial period and eight days

Impact of tropical cyclones on a baroclinic jet in the ocean

The initial evolution of a baroclinic jet under influence of a barotropic flow induced by the tropical cyclones is considered using a two-layer model and the thin-jet approximation. In spite of antisymmetric structure of the barotropic flow, the jet meander growth due to the barotropic flow advection is shown to favor an anticyclonic meander to the right of the storm track. This enhancement of the anticyclonic meander is found to be related to the dispersion properties of frontal waves along the jet described by the thin-jet theory and coupling with deep eddies developing in the lower layer during the jet meandering.У рамках двошарової моделі та в наближенні тонкого струменя розглядається еволюція бароклинного струменя, викликаного баротропною течією, індукованою тропічним циклоном. Показано, що, не дивлячись на антисиметричну структуру баротропної течії, її адвекція призводить до меандрування бароклинного струменя та до зростання головним чином антициклонічного меандру праворуч від штормтрека. Знайдено, що посилення антициклонічного меандру пов'язане з дисперсійними властивостями фронтальних хвиль (які описуються у рамках теорії тонкого струменя) і з взаємодією з глибинними вихорами, які розвиваються в нижньому шарі океану при меандруванні бароклинного струменю.В рамках двухслойной модели и в приближении тонкой струи рассматривается эволюция бароклинной струи, вызванной баротропным течением, индуцированным тропическим циклоном. Показано, что, несмотря на антисимметричную структуру баротропного течения, его адвекция приводит к меандрированию бароклинной струи и к росту главным образом антициклонического меандра справа от штормтрека. Обнаружено, что усиление антициклонического меандра связано с дисперсионными свойствами фронтальных волн (описываемых в рамках теории тонкой струи) и с взаимодействием с глубинными вихрями, развивающимися в нижнем слое океана при меандрировании бароклинной струи

Evidence of Vertical Coupling between the Kuroshio Extension and Topographically Controlled Deep Eddies

Strong energy in the 30–60 day band was observed using 39 deep pressure and current records from the Kuroshio Extension System Study (KESS). Energy in this band accounted for 25–50% of the total deep-pressure variance and was strongest under the Kuroshio Extension jet axis. Often, deep-pressure anomalies propagated into the region from the north-northeast and locally intensified as they passed under and interacted with the Kuroshio Extension. The topographically controlled deep-pressure anomalies translate nearly along lines of constant f/H. Statistically significant coherence between 30–60 day upper- and deep-ocean streamfunction anomalies demonstrated that there was strong vertical coupling in that time band. Twenty-five percent of the total upper-ocean streamfunction variance was contained within the 30–60 day band near the Kuroshio Extension. Joint CEOFs of the upper- and deep-ocean streamfunctions revealed that near the axis of the Kuroshio Extension the phases were laterally offset alongstream, with the deep ocean leading the upper ocean. This arrangement is attributed to producing joint development of upper-ocean meanders and deep-pressure anomalies.A numerical process model simulated the interaction of barotropic TRWs with an eastward-flowing baroclinic jet. When the TRWs, used as a surrogate for topographically steered deep-pressure anomalies, passed under the jet, they intensified and upper-ocean meanders steepened, much like the observed interactions. The model illustrates how the interaction between TRWs and an eastward-flowing jet, at its simplest level, can reproduce many of the major traits of our observations. The Ocean General Circulation Model for the Earth Simulator also showed similar processes in the 30–60 day band in the KESS region. The strongest variance in the deep fields occurred under the Kuroshio Extension. Upper and deep low- and high-pressure anomalies propagated south southwestward across the Kuroshio Extension, with model phase speeds and wavelengths matching the KESS observations

The Dok Cold Eddy

Current and temperature patterns in the Ulleung Basin of the Japan/East Sea are examined using acoustic travel-time measurements from an array of pressure-gauge-equipped inverted echo sounders moored between June 1999 and July 2001. The focus here is the formation and behavior of a persistent cold eddy observed south of Dok Island, referred to as the Dok Cold Eddy (DCE), and meandering of the Subpolar Front. The DCE is typically about 60 km in diameter and originates from the pinching off of a Subpolar Front meander between Ulleung and Dok Islands. After formation, the DCE dwells southwest of Dok Island for 1–6 months before propagating westward toward Korea, where it deflects the path of the East Korean Warm Current (EKWC). Four such DCE propagation events between January and June 2000 each deflected the EKWC, and after the fourth deflection the EKWC changed paths and flowed westward along the Japanese shelf as the “Offshore Branch” from June through November 2000. Beginning in March 2001, a deep, persistent meander of the Subpolar Front developed and oscillated with a period near 60 days, resulting in the deformation and northwestward displacement of the Ulleung Eddy. Satellite-altimeter data suggest that the Ulleung Eddy may have entered the northern Japan/East Sea. The evolution of this meander is compared with thin-jet nonlinear dynamics described by the modified Korteweg–deVries equation