260 research outputs found
A further study of elastic foundation models
Response expressions for elastic foundation model
Development of a CCD for ultraviolet imaging using a CCD photocathode combination
CCD in the electron-in mode, coupled with a bi-alkali photocathode to produce UV photon conversion, provides the following desirable features: (1) high UV response of the bi-alkali photocathode; (2) excellent imaging quality of a CCD area array; and (3) high signal-to-noise ratio due to the EBS (electron bombarded silicon) gain of the CCD operating in a tube configuration. This paper describes the rationale and progress made in developing a CCD for use as an UV imager
Determining North Atlantic meridional transport variability from pressure on the western boundary: a model investigation.
In this paper we investigate the possibility of determining North
Atlantic meridional transport variability using pressure on the western boundary, focusing on the 42degN latitude of the Halifax WAVE array. We start by
reviewing the theoretical foundations of this approach. Next we present results from a model analysis, both statistical and dynamic, that demonstrate
the feasibility of the approach. We consider how well we can quantify the meridional transport variability at 42degN given complete knowledge of bottom pressure across the basin, and to what degree this quantification is degraded by first ignoring the effect of intervening topography, and then by using only bottom pressure on the western boundary. We find that for periods of greater
than one year we can recover more than 90% of the variability of the main
overturning cell at 42degN using only the western boundary pressure, provided
we remove the depth-average boundary pressure signal. This signal arises from
a basin mode of bottom pressure variability, which has power at all timescales,
but that does not in truth have a meridional transport signal associated with
it, and from the geostrophic depth-independent compensation of the Ekman
transport. An additional benefit of the removal of the depth-average pressure is that this high-frequency Ekman signal, which is essentially noise as
far as monitoring the MOC for climatically important changes is concerned,
is clearly separated from other modes
Influence of the Soret effect on convection of binary fluids
Convection in horizontal layers of binary fluids heated from below and in
particular the influence of the Soret effect on the bifurcation properties of
extended stationary and traveling patterns that occur for negative Soret
coupling is investigated theoretically. The fixed points corresponding to these
two convection structures are determined for realistic boundary conditions with
a many mode Galerkin scheme for temperature and concentration and an accurate
one mode truncation of the velocity field. This solution procedure yields the
stable and unstable solutions for all stationary and traveling patterns so that
complete phase diagrams for the different convection types in typical binary
liquid mixtures can easily be computed. Also the transition from weakly to
strongly nonlinear states can be analyzed in detail. An investigation of the
concentration current and of the relevance of its constituents shows the way
for a simplification of the mode representation of temperature and
concentration field as well as for an analytically manageable few mode
description.Comment: 30 pages, 12 figure
Generation and Structure of Solitary Rossby Vortices in Rotating Fluids
The formation of zonal flows and vortices in the generalized
Charney-Hasegawa-Mima equation is studied. We focus on the regime when the size
of structures is comparable to or larger than the deformation (Rossby) radius.
Numerical simulations show the formation of anticyclonic vortices in unstable
shear flows and ring-like vortices with quiescent cores and vorticity
concentrated in a ring. Physical mechanisms that lead to these phenomena and
their relevance to turbulence in planetary atmospheres are discussed.Comment: 3 pages in REVTeX, 5 postscript figures separately, submitted to
Phys. Rev.
Dispersive stabilization of the inverse cascade for the Kolmogorov flow
It is shown by perturbation techniques and numerical simulations that the
inverse cascade of kink-antikink annihilations, characteristic of the
Kolmogorov flow in the slightly supercritical Reynolds number regime, is halted
by the dispersive action of Rossby waves in the beta-plane approximation. For
beta tending to zero, the largest excited scale is proportional to the
logarithm of one over beta and differs strongly from what is predicted by
standard dimensional phenomenology which ignores depletion of nonlinearity.Comment: 4 pages, LATEX, 3 figures. v3: revised version with minor correction
Recent Developments in Understanding Two-dimensional Turbulence and the Nastrom-Gage Spectrum
Two-dimensional turbulence appears to be a more formidable problem than
three-dimensional turbulence despite the numerical advantage of working with
one less dimension. In the present paper we review recent numerical
investigations of the phenomenology of two-dimensional turbulence as well as
recent theoretical breakthroughs by various leading researchers. We also review
efforts to reconcile the observed energy spectrum of the atmosphere (the
spectrum) with the predictions of two-dimensional turbulence and
quasi-geostrophic turbulence.Comment: Invited review; accepted by J. Low Temp. Phys.; Proceedings for
Warwick Turbulence Symposium Workshop on Universal features in turbulence:
from quantum to cosmological scales, 200
Stirring by small-scale vortices caused by patchy mixing
Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 1245-1262, doi:10.1175/JPO2713.1.Evidence is presented that lateral dispersion on scales of 1–10 km in the stratified waters of the continental shelf may be significantly enhanced by stirring by small-scale geostrophic motions caused by patches of mixed fluid adjusting in the aftermath of diapycnal mixing events. Dye-release experiments conducted during the recent Coastal Mixing and Optics (CMO) experiment provide estimates of diapycnal and lateral dispersion. Microstructure observations made during these experiments showed patchy turbulence on vertical scales of 1–10 m and horizontal scales of a few hundred meters to a few kilometers. Momentum scaling and a simple random walk formulation were used to estimate the effective lateral dispersion caused by motions resulting from lateral adjustment following episodic mixing events. It is predicted that lateral dispersion is largest when the scale of mixed patches is on the order of the internal Rossby radius of deformation, which seems to have been the case for CMO. For parameter values relevant to CMO, lower-bound estimates of the effective lateral diffusivity by this mechanism ranged from 0.1 to 1 m2s−1. Revised estimates after accounting for the possibility of long-lived motions were an order of magnitude larger and ranged from 1 to 10 m2s−1. The predicted dispersion is large enough to explain the observed lateral dispersion in all four CMO dye-release experiments examined.The Coastal Mixing and Optics
dye studies were funded by the Office of Naval Research
under Grants N00014-95-1-0633 (tracer experiments)
and N00014-95-1-1063 (AASERT fellowship).
Additional analysis was also performed under ONR
Grant N00014-01-1-0984
Turbulent spectrum of the Earth's ozone field
The Total Ozone Mapping Spectrometer (TOMS) database is subjected to an
analysis in terms of the Karhunen-Loeve (KL) empirical eigenfunctions. The
concentration variance spectrum is transformed into a wavenumber spectrum, . In terms of wavenumber is shown to be in the
inverse cascade regime, in the enstrophy cascade regime with the
spectral {\it knee} at the wavenumber of barotropic instability.The spectrum is
related to known geophysical phenomena and shown to be consistent with physical
dimensional reasoning for the problem. The appropriate Reynolds number for the
phenomena is .Comment: RevTeX file, 4 pages, 4 postscript figures available upon request
from Richard Everson <[email protected]
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Up-gradient eddy fluxes of potential vorticity near the subtropical jet
The role of eddy fluxes in the general circulation is
often approached by treating eddies as (macro)turbulence.
In this approach, the eddies act to diffuse certain quasiconservative quantities, such as potential vorticity (PV), along isentropic surfaces in the free atmosphere. The eddy fluxes are determined primarily by the eddy diffusivities and are necessarily down-gradient of the basic state PV field. Support for the (macro)turbulence approach stems from the fact that the eddy fluxes of PV in the free atmosphere are generally down-gradient in the long-term mean. Here we call attention to a pronounced and significant region of upgradient eddy PV fluxes on the poleward flank of the jet core in both hemispheres. The region of up-gradient (i.e., notionally “antidiffusive”) eddy PV fluxes is most pronounced during the winter and spring seasons and partially contradicts the turbulence approach described above. Analyses of the PV variance (potential enstrophy) budget suggest that the up-gradient PV fluxes represent local wave decay and are maintained by poleward fluxes of PV variance. Finite-amplitude effects thus represent leading order contributions to the PV variance budget, whereas dissipation is only of secondary importance locally. The appearance of up-gradient PV fluxes in the long-term mean is associated with the poleward shift of the jet—and thus the region of wave decay relative to wave growth—following wave-breaking events
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