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A M Dziewonski - One of the best experts on this subject based on the ideXlab platform.
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the shear wave Velocity Structure in the upper mantle beneath eurasia
Geophysical Journal International, 2008Co-Authors: B Kustowski, Goran Ekstrom, A M DziewonskiAbstract:SUMMARY We develop an approach that allows us to invert for the mantle Velocity Structure within a finely parametrized region as a perturbation with respect to a low-resolution, global tomographic model. We implement this technique to investigate the upper-mantle Structure beneath Eurasia and present a new model of shear wave Velocity, parametrized laterally using spherical splines with ∼2.9 ◦ spacing in Eurasia and ∼11.5 ◦ spacing elsewhere. The model is obtained from a combined data set of surface wave phase velocities, long-period waveforms and body-wave traveltimes. We identify many features as narrow as few hundred kilometres in diameter, such as subducting slabs in eastern Eurasia and slow-Velocity anomalies beneath tectonically active regions. In contrast to regional studies in which these features have been identified, our model encompasses the Structure of the entire Eurasian continent. Furthermore, including mantleand body-wave waveforms helped us constrain Structures at depths larger than 250 km, which are poorly resolved in earlier models. We find that up to +9 per cent faster-than-average anomalies within the uppermost ∼200 km of the mantle beneath cratons and some orogenic regions are separated by a sharp gradient zone from deeper, + 1t o+2 per cent anomalies. We speculate that this gradient zone may represent a boundary separating the lithosphere from the continental root, which might be compositionally distinct from the overlying lithosphere and remain stable either due to its compositional buoyancy or due to higher viscosity compared with the suboceanic mantle. Our regional model of anisotropy is not significantly different from the global one.
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radially anisotropic shear Velocity Structure of the upper mantle globally and beneath north america
Journal of Geophysical Research, 2008Co-Authors: Meredith Nettles, A M DziewonskiAbstract:[1] A surface wave dispersion data set of unprecedented size is used to obtain a variable-resolution model of the radially anisotropic shear wave Velocity Structure of the upper mantle beneath North America and globally. Love and Rayleigh wave phase velocities for periods in the range 35–150 s constrain a three-dimensional model of Velocity variations on a length scale of a few hundred kilometers within the North American continent and a few thousand kilometers globally. The short- and long-wavelength models are determined simultaneously. Long-period surface wave phase velocities (200–350 s) are used to help constrain longer-wavelength and transition zone Structure. Laterally varying Velocity sensitivity kernels are used to account for the dependence of the Velocity sensitivity on lateral variations in crust and mantle Velocity Structure. The sensitivity kernels are updated in several iterations to avoid nonlinearities associated with the inverse problem for the determination of mantle Structure. Variations in isotropic Velocity in the uppermost several hundred kilometers of the mantle are found to correlate well with surface tectonic features. Within the North American craton, the locations of strongest radial anisotropy generally correlate with the locations of fastest isotropic Velocity. Variations in radial anisotropy show a clear continent-ocean signature. Strong anisotropy occurs at shallow depths (<100 km) under the continents, with a secondary peak found at a depth of ∼200 km. Maximum anisotropy under the oceans occurs at a depth of ∼125 km, with no secondary maximum. Combined interpretation of isotropic and anisotropic continent-ocean differences suggests a different role for the low-Velocity zone under continental and oceanic regions.
Domenico Anfossi - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Lagrangian Velocity Structure Function Constant C_0 by Large-Eddy Simulation
Boundary-Layer Meteorology, 2006Co-Authors: Umberto Rizza, Cristina Mangia, Jonas C. Carvalho, Domenico AnfossiAbstract:The inertial subrange Kolmogorov constant C _0, which determines the effective turbulent diffusion in Velocity space, plays an important role in the Lagrangian modelling of pollutants. A wide range of values of the constant are found in the literature, most of them determined at low Reynolds number and/or under different assumptions. Here we estimate the constant C _0 by tracking an ensemble of Lagrangian particles in a planetary boundary layer simulated with a large-eddy simulation model and analysing the Lagrangian Velocity Structure function in the inertial subrange. The advantage of this technique is that it easily allows Reynolds numbers to be achieved typical of convective turbulent flows. Our estimates of C _0 is C _0=4.3±0.3 consistent with values found in the literature
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Estimation of the Lagrangian Velocity Structure Function Constant C0 by Large-Eddy Simulation
Boundary-Layer Meteorology, 2006Co-Authors: Umberto Rizza, Cristina Mangia, Jonas C. Carvalho, Domenico AnfossiAbstract:The inertial subrange Kolmogorov constant C0, which determines the effective tur- bulent diffusion in Velocity space, plays an important role in the Lagrangian modelling of pollutants. A wide range of values of the constant are found in the literature, most of them determined at low Reynolds number and/or under different assumptions. Here we estimate the constant C0 by tracking an ensemble of Lagrangian particles in a planetary boundary layer simulated with a large-eddy simulation model and analysing the Lagrangian Velocity Structure function in the inertial subrange. The advantage of this technique is that it easily allows Reynolds numbers to be achieved typical of convective turbulent flows. Our estimates of C0 is C0 = 4.3 ± 0.3 consistent with values found in the literature.
Shuming Du - One of the best experts on this subject based on the ideXlab platform.
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UNIVERSALITY OF THE LAGRANGIAN Velocity Structure FUNCTION CONSTANT (C0) ACROSS DIFFERENT KINDS OF TURBULENCE
Boundary-Layer Meteorology, 1997Co-Authors: Shuming DuAbstract:In this paper, we evaluate the Lagrangian Velocity Structure function constant, C0, in the inertial subrange by comparing experimental diffusion data and simulation results obtained with applicable Lagrangian stochastic models. We find in several different flows (grid turbulence, laboratory boundary-layer flow and the atmospheric surface layer under neutral stratification) the value for C0 is 3.0 ± 0.5. We also identify the reasons responsible for earlier studies having not reached the present result.
Umberto Rizza - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Lagrangian Velocity Structure Function Constant C_0 by Large-Eddy Simulation
Boundary-Layer Meteorology, 2006Co-Authors: Umberto Rizza, Cristina Mangia, Jonas C. Carvalho, Domenico AnfossiAbstract:The inertial subrange Kolmogorov constant C _0, which determines the effective turbulent diffusion in Velocity space, plays an important role in the Lagrangian modelling of pollutants. A wide range of values of the constant are found in the literature, most of them determined at low Reynolds number and/or under different assumptions. Here we estimate the constant C _0 by tracking an ensemble of Lagrangian particles in a planetary boundary layer simulated with a large-eddy simulation model and analysing the Lagrangian Velocity Structure function in the inertial subrange. The advantage of this technique is that it easily allows Reynolds numbers to be achieved typical of convective turbulent flows. Our estimates of C _0 is C _0=4.3±0.3 consistent with values found in the literature
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Estimation of the Lagrangian Velocity Structure Function Constant C0 by Large-Eddy Simulation
Boundary-Layer Meteorology, 2006Co-Authors: Umberto Rizza, Cristina Mangia, Jonas C. Carvalho, Domenico AnfossiAbstract:The inertial subrange Kolmogorov constant C0, which determines the effective tur- bulent diffusion in Velocity space, plays an important role in the Lagrangian modelling of pollutants. A wide range of values of the constant are found in the literature, most of them determined at low Reynolds number and/or under different assumptions. Here we estimate the constant C0 by tracking an ensemble of Lagrangian particles in a planetary boundary layer simulated with a large-eddy simulation model and analysing the Lagrangian Velocity Structure function in the inertial subrange. The advantage of this technique is that it easily allows Reynolds numbers to be achieved typical of convective turbulent flows. Our estimates of C0 is C0 = 4.3 ± 0.3 consistent with values found in the literature.
A M Reynolds - One of the best experts on this subject based on the ideXlab platform.
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comments on the universality of the lagrangian Velocity Structure function constant c0 across different kinds of turbulence
Boundary-Layer Meteorology, 1998Co-Authors: A M ReynoldsAbstract:Recently Du ( Boundary-Layer Meteorology 83, 207–219, 1997) estimated the value of the Lagrangian Velocity Structure constant, C0, in the inertial subrange by comparing experimental diffusion data and simulation results obtained with the one-dimensional form of Thomson's model ( J. Fluid Mech. 180, 529–556, 1987). Du reported that for several different flows (grid turbulence, a wind-tunnel boundary layer and the atmospheric surface layer under neutral stratification) the value of C0 is 3.0±0.5. Here, it is shown that optimal model agreement with experimental diffusion data for the wind-tunnel boundary layer is, in fact, obtained when C0=5.0 ± 0.5. It is also shown that accounting for the skewness of Velocity statistics and finite Reynolds number effects does not significantly change this estimate for the value of C0. It is suggested that one-dimensional Lagrangian stochastic models are inconsistent with the supposed universality of C0.
