The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Stephan Andreas Fueglistaler - One of the best experts on this subject based on the ideXlab platform.
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Kelvin Waves and shear‐flow turbulent mixing in the TTL in (re‐)analysis data
Geophysical Research Letters, 2011Co-Authors: T. J. Flannaghan, Stephan Andreas FueglistalerAbstract:[1] It has been suggested that the tropical tropopause layer (TTL) may be affected by mixing from shear-flow instability in connection with Kelvin Waves. It is shown that the revised Louis-scheme (used in operational analyses and ERA-40 and ERA-Interim of ECMWF) strongly responds to Kelvin wave perturbations, and average mixing is maximized where Kelvin wave amplitudes are largest (Indian ocean/Maritime continent). Conversely, the Monin-Obukhov scheme predicts fewer, but more intense mixing events that maximize further East. For the TTL, the mixing predicted by the two schemes is similar and small, but locally the models predict shear-flow mixing sufficient to yield net diabatic descent over the aforementioned regions. The data analyzed here remains inconclusive about which scheme captures reality better, rendering the role of Kelvin Waves for shear-flow instability uncertain. The mixing schemes' sensitivity to Kelvin Waves has implications for the dissipation of Kelvin Waves in models and analyzed meteorological data.
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Kelvin Waves and shear flow turbulent mixing in the ttl in re analysis data
Geophysical Research Letters, 2011Co-Authors: T. J. Flannaghan, Stephan Andreas FueglistalerAbstract:[1] It has been suggested that the tropical tropopause layer (TTL) may be affected by mixing from shear-flow instability in connection with Kelvin Waves. It is shown that the revised Louis-scheme (used in operational analyses and ERA-40 and ERA-Interim of ECMWF) strongly responds to Kelvin wave perturbations, and average mixing is maximized where Kelvin wave amplitudes are largest (Indian ocean/Maritime continent). Conversely, the Monin-Obukhov scheme predicts fewer, but more intense mixing events that maximize further East. For the TTL, the mixing predicted by the two schemes is similar and small, but locally the models predict shear-flow mixing sufficient to yield net diabatic descent over the aforementioned regions. The data analyzed here remains inconclusive about which scheme captures reality better, rendering the role of Kelvin Waves for shear-flow instability uncertain. The mixing schemes' sensitivity to Kelvin Waves has implications for the dissipation of Kelvin Waves in models and analyzed meteorological data.
Carlo F. Barenghi - One of the best experts on this subject based on the ideXlab platform.
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Leapfrogging Kelvin Waves
Physical Review Fluids, 2016Co-Authors: Niklas Hietala, Risto Hänninen, Hayder Salman, Carlo F. BarenghiAbstract:Two vortex rings can form a localized configuration whereby they continually pass through one another in an alternating fashion. This phenomenon is called leapfrogging. Using parameters suitable for superfluid helium-4, we describe a recurrence phenomenon that is similar to leapfrogging, which occurs for two coaxial straight vortex filaments with the same Kelvin wave mode. For small-amplitude Kelvin Waves we demonstrate that our full Biot-Savart simulations closely follow predictions obtained from a simpified model that provides an analytical approximation developed for nearly parallel vortices. Our results are also relevant to thin-cored helical vortices in classical fluids.
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Interaction and decay of Kelvin Waves in the Gross-Pitaevskii model
arXiv: Fluid Dynamics, 2013Co-Authors: Davide Proment, Carlo F. Barenghi, Miguel OnoratoAbstract:By solving numerically the governing Gross-Pitaevskii equation, we study the dynamics of Kelvin Waves on a superfluid vortex. After determining the dispersion relation, we monitor the turbulent decay of Kelvin Waves with energy initially concentrated at large length scales. At intermediate length scales, we find that the decay is consistent with scaling predictions of theoretical models. Finally we report the unexpected presence of large-length scale phonons in the system.
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Turbulent cascade of Kelvin Waves on vortex filaments
Journal of Physics: Conference Series, 2011Co-Authors: Andrew W. Baggaley, Carlo F. BarenghiAbstract:By numerically integrating in time the motion of vortex filaments, we study how the nonlinear interaction of Kelvin Waves along vortices generates Kelvin Waves of larger and larger wavenumbers (smaller and smaller wavelength). At sufficiently large wavenumbers the angular velocity of the vortices is large enough that kinetic energy is lost by sound emission. This turbulent cascade of Kelvin Waves should explain why turbulence, generated in superfluid helium at very low temperature near absolute zero, quickly decays, despite the lack of any viscous dissipation.
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spectrum of turbulent Kelvin Waves cascade in superfluid helium
Physical Review B, 2011Co-Authors: Andrew W. Baggaley, Carlo F. BarenghiAbstract:To explain the observed decay of superfluid turbulence at very low temperature, it has been proposed that a cascade of Kelvin Waves (analogous to the classical Kolmogorov cascade) transfers kinetic energy to length scales that are small enough that sound can be radiated away. We report results of numerical simulations of the interaction of quantized vortex filaments. We observe the development of the Kelvin-Waves cascade, and compute the statistics of the curvature, the amplitude spectrum (which we compare with competing theories), and the fractal dimension.
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Anomalous translational velocity of vortex ring with finite-amplitude Kelvin Waves.
Physical Review E, 2006Co-Authors: Carlo F. Barenghi, Risto Hänninen, Makoto TsubotaAbstract:We consider finite-amplitude Kelvin Waves on an inviscid vortex assuming that the vortex core has infinitesimal thickness. By numerically solving the governing Biot-Savart equation of motion, we study how the frequency of the Kelvin Waves and the velocity of the perturbed ring depend on the Kelvin wave amplitude. In particular, we show that, if the amplitude of the Kelvin Waves is sufficiently large, the perturbed vortex ring moves backwards.
T. J. Flannaghan - One of the best experts on this subject based on the ideXlab platform.
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tracking Kelvin Waves from the equatorial troposphere into the stratosphere
Journal of Geophysical Research, 2012Co-Authors: T. J. Flannaghan, S FueglistalerAbstract:[1] Convectively coupled Kelvin Waves in the troposphere have a vertically propagating component which propagates through the tropical tropopause layer into the stratosphere. In the tropical tropopause layer above the typical top of deep convection, these Waves propagate as dry Waves. In the stratosphere they contribute to the forcing of the stratospheric quasi-biennial oscillation. Here, we address the challenge to track individual Waves in a region where both static stability and background wind rapidly change with a new algorithm that operates in real space and uses the full longitude/height/time information available to reliably identify Kelvin Waves. We argue that our algorithm overcomes inherent ambiguities in previously published methods. Specifically, our algorithm cleanly separates wave activity and number of Waves, and successfully tracks Waves also in regions where background wind reduces wave amplitudes. Applied to ECMWF reanalysis data for the period 1989–2011, we obtain a statistical description of Kelvin wave propagation that shows propagation through the TTL into the stratosphere occurs predominantly over the Indian Ocean and Atlantic.
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Kelvin Waves and shear‐flow turbulent mixing in the TTL in (re‐)analysis data
Geophysical Research Letters, 2011Co-Authors: T. J. Flannaghan, Stephan Andreas FueglistalerAbstract:[1] It has been suggested that the tropical tropopause layer (TTL) may be affected by mixing from shear-flow instability in connection with Kelvin Waves. It is shown that the revised Louis-scheme (used in operational analyses and ERA-40 and ERA-Interim of ECMWF) strongly responds to Kelvin wave perturbations, and average mixing is maximized where Kelvin wave amplitudes are largest (Indian ocean/Maritime continent). Conversely, the Monin-Obukhov scheme predicts fewer, but more intense mixing events that maximize further East. For the TTL, the mixing predicted by the two schemes is similar and small, but locally the models predict shear-flow mixing sufficient to yield net diabatic descent over the aforementioned regions. The data analyzed here remains inconclusive about which scheme captures reality better, rendering the role of Kelvin Waves for shear-flow instability uncertain. The mixing schemes' sensitivity to Kelvin Waves has implications for the dissipation of Kelvin Waves in models and analyzed meteorological data.
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Kelvin Waves and shear flow turbulent mixing in the ttl in re analysis data
Geophysical Research Letters, 2011Co-Authors: T. J. Flannaghan, Stephan Andreas FueglistalerAbstract:[1] It has been suggested that the tropical tropopause layer (TTL) may be affected by mixing from shear-flow instability in connection with Kelvin Waves. It is shown that the revised Louis-scheme (used in operational analyses and ERA-40 and ERA-Interim of ECMWF) strongly responds to Kelvin wave perturbations, and average mixing is maximized where Kelvin wave amplitudes are largest (Indian ocean/Maritime continent). Conversely, the Monin-Obukhov scheme predicts fewer, but more intense mixing events that maximize further East. For the TTL, the mixing predicted by the two schemes is similar and small, but locally the models predict shear-flow mixing sufficient to yield net diabatic descent over the aforementioned regions. The data analyzed here remains inconclusive about which scheme captures reality better, rendering the role of Kelvin Waves for shear-flow instability uncertain. The mixing schemes' sensitivity to Kelvin Waves has implications for the dissipation of Kelvin Waves in models and analyzed meteorological data.
Christopher J Schreck - One of the best experts on this subject based on the ideXlab platform.
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Convectively Coupled Kelvin Waves and Tropical Cyclogenesis in a Semi-Lagrangian Framework
Monthly Weather Review, 2016Co-Authors: Christopher J SchreckAbstract:AbstractThis study examines how convectively coupled Kelvin Waves interact with the semi-Lagrangian circulation of easterly Waves to modulate tropical cyclogenesis. Recent studies have shown that fewer tropical cyclones form in the three days before passage of the Kelvin wave’s peak convection and more develop in the three days thereafter. Separately, other studies have identified the recirculation of moisture and vorticity within easterly Waves using a semi-Lagrangian frame of reference. That framework is achieved by subtracting the easterly wave phase speed from the earth-relative winds. This study combines these recent findings by testing whether the equatorial westerlies from Kelvin Waves can help close the semi-Lagrangian circulation.Past studies have shown that Kelvin Waves tilt westward with height in the troposphere such that equatorial westerlies build upward from the surface in the days following the convective peak. This study shows that the easterly wave’s semi-Lagrangian closed circulation gr...
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Kelvin Waves and Tropical Cyclogenesis: A Global Survey
Monthly Weather Review, 2015Co-Authors: Christopher J SchreckAbstract:AbstractConvectively coupled atmospheric Kelvin Waves are among the most prominent sources of synoptic-scale rainfall variability in the tropics, but large uncertainties surround their role in tropical cyclogenesis. This study identifies the modulation of tropical cyclones relative to the passage of a Kelvin wave’s peak rainfall (i.e., its crest) in each basin. Tropical cyclogenesis is generally inhibited for 3 days before the crest and enhanced for 3 days afterward. Composites of storms forming in the most favorable lags illustrate the dynamical impacts of the Waves. In most basins, the tropical cyclone actually forms during the convectively suppressed phase of the wave. The 850-hPa equatorial westerly anomalies provide the cyclonic vorticity for the nascent storm, and 200-hPa easterly anomalies enhance the outflow. The wind anomalies persist at both levels longer than the Kelvin wave’s period and are often related to the Madden–Julian oscillation (MJO). The onset of these wind anomalies occurs with the ...
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Tropical Cyclogenesis Associated with Kelvin Waves and the Madden–Julian Oscillation
Monthly Weather Review, 2011Co-Authors: Christopher J Schreck, John MolinariAbstract:AbstractThe Madden–Julian oscillation (MJO) influences tropical cyclone formation around the globe. Convectively coupled Kelvin Waves are often embedded within the MJO, but their role in tropical cyclogenesis remains uncertain. This case study identifies the influences of the MJO and a series of Kelvin Waves on the formation of two tropical cyclones.Typhoons Rammasun and Chataan developed in the western North Pacific on 28 June 2002. Two weeks earlier, conditions had been unfavorable for tropical cyclogenesis because of uniform trade easterlies and a lack of organized convection. The easterlies gave way to equatorial westerlies as the convective envelope of the Madden–Julian oscillation moved into the region. A series of three Kelvin Waves modulated the development of the westerlies. Cyclonic potential vorticity (PV) developed in a strip between the growing equatorial westerlies and the persistent trade easterlies farther poleward. Rammasun and Chataan emerged from the apparent breakdown of this strip.The...
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tropical cyclogenesis associated with Kelvin Waves and the madden julian oscillation
Monthly Weather Review, 2011Co-Authors: Christopher J Schreck, John MolinariAbstract:AbstractThe Madden–Julian oscillation (MJO) influences tropical cyclone formation around the globe. Convectively coupled Kelvin Waves are often embedded within the MJO, but their role in tropical cyclogenesis remains uncertain. This case study identifies the influences of the MJO and a series of Kelvin Waves on the formation of two tropical cyclones.Typhoons Rammasun and Chataan developed in the western North Pacific on 28 June 2002. Two weeks earlier, conditions had been unfavorable for tropical cyclogenesis because of uniform trade easterlies and a lack of organized convection. The easterlies gave way to equatorial westerlies as the convective envelope of the Madden–Julian oscillation moved into the region. A series of three Kelvin Waves modulated the development of the westerlies. Cyclonic potential vorticity (PV) developed in a strip between the growing equatorial westerlies and the persistent trade easterlies farther poleward. Rammasun and Chataan emerged from the apparent breakdown of this strip.The...
Marc Brachet - One of the best experts on this subject based on the ideXlab platform.
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helicity topology and Kelvin Waves in reconnecting quantum knots
Physical Review A, 2016Co-Authors: Clark P Di Leoni, P D Mininni, Marc BrachetAbstract:Helicity is a topological invariant that measures the linkage and knottedness of lines, tubes and ribbons. As such, it has found myriads of applications in astrophysics and solar physics, in fluid dynamics, in atmospheric sciences, and in biology. In quantum flows, where topology-changing reconnection events are a staple, helicity appears as a key quantity to study. However, the usual definition of helicity is not well posed in quantum vortices, and its computation based on counting links and crossings of vortex lines can be downright impossible to apply in complex and turbulent scenarios. We present a new definition of helicity which overcomes these problems. With it, we show that only certain reconnection events conserve helicity. In other cases helicity can change abruptly during reconnection. Furthermore, we show that these events can also excite Kelvin Waves, which slowly deplete helicity as they interact nonlinearly, thus linking the theory of vortex knots with observations of quantum turbulence.
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spatiotemporal detection of Kelvin Waves in quantum turbulence simulations
Physical Review A, 2015Co-Authors: Clark P Di Leoni, P D Mininni, Marc BrachetAbstract:We present evidence of Kelvin excitations in space-time resolved spectra of numerical simulations of quantum turbulence. Kelvin Waves are transverse and circularly polarized Waves that propagate along quantized vortices, for which the restitutive force is the tension of the vortex line, and which play an important role in theories of superfluid turbulence. We use the Gross-Pitaevskii equation to model quantum flows, letting an initial array of well-organized vortices develop into a turbulent bundle of intertwined vortex filaments. By achieving high spatial and temporal resolution we are able to calculate space-time resolved mass density and kinetic energy spectra. Evidence of Kelvin and sound Waves is clear in both spectra. Identification of the Waves allows us to extract the spatial spectrum of Kelvin Waves, clarifying their role in the transfer of energy.
