1,033 research outputs found
Marginal sea overflows and the upper ocean interaction
Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 39 (2009): 387-403, doi:10.1175/2008JPO3934.1.Marginal sea overflows and the overlying upper ocean are coupled in the vertical by two distinct mechanisms—by an interfacial mass flux from the upper ocean to the overflow layer that accompanies entrainment and by a divergent eddy flux associated with baroclinic instability. Because both mechanisms tend to be localized in space, the resulting upper ocean circulation can be characterized as a β plume for which the relevant background potential vorticity is set by the slope of the topography, that is, a topographic β plume.
The entrainment-driven topographic β plume consists of a single gyre that is aligned along isobaths. The circulation is cyclonic within the upper ocean (water columns are stretched). The transport within one branch of the topographic β plume may exceed the entrainment flux by a factor of 2 or more.
Overflows are likely to be baroclinically unstable, especially near the strait. This creates eddy variability in both the upper ocean and overflow layers and a flux of momentum and energy in the vertical. In the time mean, the eddies accompanying baroclinic instability set up a double-gyre circulation in the upper ocean, an eddy-driven topographic β plume. In regions where baroclinic instability is growing, the momentum flux from the overflow into the upper ocean acts as a drag on the overflow and causes the overflow to descend the slope at a steeper angle than what would arise from bottom friction alone.
Numerical model experiments suggest that the Faroe Bank Channel overflow should be the most prominent example of an eddy-driven topographic β plume and that the resulting upper-layer transport should be comparable to that of the overflow. The overflow-layer eddies that accompany baroclinic instability are analogous to those observed in moored array data. In contrast, the upper layer of the Mediterranean overflow is likely to be dominated more by an entrainment-driven topographic β plume. The difference arises because entrainment occurs at a much shallower location for the Mediterranean case and the background potential vorticity gradient of the upper ocean is much larger.SK’s support during the time of his Ph.D.
research in the MIT/WHOI Joint Program was provided
by the National Science Foundation through
Grant OCE04-24741. JP and JY have also received
support from the Climate Process Team on Gravity
Current Entrainment, NSF Grant OCE-0611530. JY has
also been supported by NSF Grant OCE-0351055
Double scaling and intermittency in shear dominated flows
The Refined Kolmogorov Similarity Hypothesis is a valuable tool for the
description of intermittency in isotropic conditions. For flows in presence of
a substantial mean shear, the nature of intermittency changes since the process
of energy transfer is affected by the turbulent kinetic energy production
associated with the Reynolds stresses. In these conditions a new form of
refined similarity law has been found able to describe the increased level of
intermittency which characterizes shear dominated flows. Ideally a length scale
associated with the mean shear separates the two ranges, i.e. the classical
Kolmogorov-like inertial range, below, and the shear dominated range, above.
However, the data analyzed in previous papers correspond to conditions where
the two scaling regimes can only be observed individually.
In the present letter we give evidence of the coexistence of the two regimes
and support the conjecture that the statistical properties of the dissipation
field are practically insensible to the mean shear. This allows for a
theoretical prediction of the scaling exponents of structure functions in the
shear dominated range based on the known intermittency corrections for
isotropic flows. The prediction is found to closely match the available
numerical and experimental data.Comment: 7 pages, 3 figures, submitted to PR
Evidence for Anisotropic Vortex Dynamics and Pauli Limitation in the Upper Critical Field of FeSe1-xTex
We have determined HC2(T) for FeSe1-xTex (x=0.52) single crystals using
resistivity measurements at high static and pulsed magnetic field, as well as
specific heat measurements up to 9T. We find that the significant anisotropy of
the initial slope of HC2(T) determined from resistivity measurements, is not
present when HC2 is determined from the specific heat results. This suggests
that the thermodynamic upper critical field is almost isotropic, and that
anisotropic vortex dynamics play a role. Further evidence of anisotropic vortex
dynamics is found in the behaviour in pulsed field. We also find that Pauli
limiting must be included in order to fit the temperature dependence of HC2,
indicating probably higher effective mass in FeSe1-xTex than in other Fe
superconductors
Orbit equivalence rigidity for ergodic actions of the mapping class group
We establish orbit equivalence rigidity for any ergodic, essentially free and
measure-preserving action on a standard Borel space with a finite positive
measure of the mapping class group for a compact orientable surface with higher
complexity. We prove similar rigidity results for a finite direct product of
mapping class groups as well.Comment: 11 pages, title changed, a part of contents remove
Exact solution of the one-dimensional ballistic aggregation
An exact expression for the mass distribution of the ballistic
aggregation model in one dimension is derived in the long time regime. It is
shown that it obeys scaling with a scaling
function for and for
. Relevance of these results to Burgers turbulence is discussed.Comment: 11 pages, 2 Postscript figure
A new scaling property of turbulent flows
We discuss a possible theoretical interpretation of the self scaling property
of turbulent flows (Extended Self Similarity). Our interpretation predicts
that, even in cases when ESS is not observed, a generalized self scaling, must
be observed. This prediction is checked on a number of laboratory experiments
and direct numerical simulations.Comment: Plain Latex, 1 figure available upon request to
[email protected]
Transient vortex events in the initial value problem for turbulence
A vorticity surge event that could be a paradigm for a wide class of bursting
events in turbulence is studied to examine how the energy cascade is
established and how this event could serve as a new test of LES turbulence
models. This vorticity surge event is tied to the formation of the energy
cascade in a direct numerical simulation by the traditional signatures of a
turbulent energy cascade such as spectra approaching -5/3 and strongly
Beltramized vortex tubes. A coherent mechanism is suggested by the nearly
simultaneous development of a maximum of the peak vorticity
, growth of the dissipation, the appearance of a helically
aligned local vortex configuration and strong, transient oscillations in the
helicity wavenumber spectrum. This coherence is also examined for two LES
models, a traditional purely dissipative eddy viscosity model and a modern
method (LANS) that respects the nonlinear transport properties of
fluids. Both LES models properly represent the spectral energy and energy
dissipation associated with this vorticity surge event. However, only the model
that preserves nonlinear fluid transport properties reproduces the helical
properties, including Beltrami-like vortex tubes.Comment: 4 pages, 6 figure
Kolmogorov Spectrum of Quantum Turbulence
There is a growing interest in the relation between classical turbulence and
quantum turbulence. Classical turbulence arises from complicated dynamics of
eddies in a classical fluid. In contrast, quantum turbulence consists of a
tangle of stable topological defects called quantized vortices, and thus
quantum turbulence provides a simpler prototype of turbulence than classical
turbulence. In this paper, we investigate the dynamics and statistics of
quantized vortices in quantum turbulence by numerically solving a modified
Gross-Pitaevskii equation. First, to make decaying turbulence, we introduce a
dissipation term that works only at scales below the healing length. Second, to
obtain steady turbulence through the balance between injection and decay, we
add energy injection at large scales. The energy spectrum is quantitatively
consistent with the Kolmogorov law in both decaying and steady turbulence.
Consequently, this is the first study that confirms the inertial range of
quantum turbulence.Comment: 14pages, 24 figures and 1 table. Appeared in Journal of the Physical
Society of Japan, Vol.74, No.12, p.3248-325
Velocity fluctuations in forced Burgers turbulence
We propose a simple method to compute the velocity difference statistics in
forced Burgers turbulence in any dimension. Within a reasonnable assumption
concerning the nucleation and coalescence of shocks, we find in particular that
the `left' tail of the distribution decays as an inverse square power, which is
compatible with numerical data. Our results are compared to those of various
recent approaches: instantons, operator product expansion, replicas.Comment: 10 pages latex, one postcript figur
Reheating and turbulence
We show that the ''turbulent'' particle spectra found in numerical
simulations of the behavior of matter fields during reheating admit a simple
interpretation in terms of hydrodynamic models of the reheating period. We
predict a particle number spectrum with for Comment: 10 pages, one figure included in tex
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