Horizontal wave number spectra of temperature in the unstably stratified oceanic surface layer

2001 ◽  
Vol 106 (C8) ◽  
pp. 16929-16946 ◽  
Author(s):  
H. W. Wijesekera ◽  
C. A. Paulson ◽  
A. Huyer
Keyword(s):  
Surface Layer ◽  
Wave Number ◽  
Oceanic Surface ◽  
Horizontal Wave

The warm oceanic surface layer: Implications for CO2fluxes and surface gas measurements

1996 ◽  
Vol 23 (24) ◽  
pp. 3575-3578 ◽  
Author(s):  
Craig L. McNeil ◽  
Liliane Merlivat
Keyword(s):  
Surface Layer ◽  
Oceanic Surface ◽  
Gas Measurements

Gravitational instability of a viscous fluid in a magnetic field

1965 ◽  
Vol 22 (3) ◽  
pp. 579-586 ◽  
Author(s):  
Chia-Shun Yih
Keyword(s):  
Magnetic Field ◽  
Viscous Fluid ◽  
Hartmann Number ◽  
Gravitational Instability ◽  
Unstable Mode ◽  
Stability Boundary ◽  
Wave Number ◽  
Symmetric Mode ◽  
Critical Stability ◽  
Horizontal Wave

The instability of a viscous fluid between two infinite vertical plates and heated from below in the presence of a magnetic field perpendicular to the plates is investigated, and the most critical stability boundary in the space of the Rayleigh number R, Hartmann number M, and the horizontal wave number a is determined. It is found that the most unstable mode is a symmetric mode with zero wave-number, and that for any M the fluid is unstable for any non-zero R, however small.

Excitation of internal waves in a stably-stratified atmosphere with considerable wind-shear

1968 ◽  
Vol 32 (1) ◽  
pp. 145-171 ◽  
Author(s):  
A. A. Townsend
Keyword(s):  
Boundary Layer ◽  
Internal Waves ◽  
Wind Shear ◽  
Wave Packets ◽  
Normal Modes ◽  
Wave Number ◽  
Spectral Energy ◽  
Air Turbulence ◽  
Wave Numbers ◽  
Horizontal Wave

The rate of generation of internal waves by a thin turbulent boundary layer was calculated in a previous paper for a stably-stratified atmosphere with no significant wind-shear outside the boundary layer by considering the excitation of normal modes of wave propagation. By using the concept of wave-packets propagating upwards from the boundary layer, the effects of wind-shear can be included. Conditions for the validity of the approximation are given. In general, the spectral distribution of wave-energy at a particular height takes large values in two bands of horizontal wave-number, one band deriving from wave-packets undergoing internal reflexion near that height and the other from wave-packets of very small local frequency that accumulate there. The ‘reflexion’ wave-numbers are dominant if the wind increases with height and the ‘accumulation’ wave-numbers if the wind initially decreases with height. The spectral energy distributions and intensities of the wave-motion are discussed in more detail for an atmosphere of uniform stability and unidirectional wind-shear. The accumulation process may lead to instability or overturning of the waves, and estimates are made of the probable scale and intensity of the ‘clear-air’ turbulence produced. An interesting point is that the rate of energy loss from the boundary layer by radiation of internal waves turns out to be comparable with the rate of production in the outer nine-tenths of the layer, both for atmospheric boundary layers and for the surface layer of the ocean. It seems likely that radiation limits the layer thickness to some extent.

scholarly journals Nonlinear hydromagnetic convection in a moderate prandtl number fluid

1981 ◽  
Vol 23 (3) ◽  
pp. 321-338 ◽  
Author(s):  
N. Riahi
Keyword(s):  
Prandtl Number ◽  
Lorentz Force ◽  
Strong Field ◽  
Inertial Force ◽  
Weak Field ◽  
Wave Number ◽  
Boundary Layer Method ◽  
Horizontal Wave ◽  
Moderate Field ◽  
Moderate Prandtl Number Fluid

Nonlinear hydromagnetic connection is investigated using the modal equations for cellular convection. The boundary layer method is used assuming large Rayleigh number R, moderate Prandtl number σ and for different ranges of the Chandrasekhar number Q. The heat flux F is determined for the value of the horizontal wave number which maximizes F. For a weak field, the inertial force dominates over the Lorentz force. F is independent of Q, but it increases with R and σ. For a moderate field, the Lorentz force is significant. F increases with R and σ and decreases as Q increases. For a strong field, the Lorentz force dominates over the inertial force. F is independent of σ, but it increases with R and decreases as Q increases.

scholarly journals Evaluating Monin-Obukhov Scaling in the Unstable Oceanic Surface Layer

2020 ◽  
Author(s):  
Zhihua Zheng ◽  
Ramsey R. Harcourt ◽  
Eric A. D’Asaro
Keyword(s):  
Surface Layer ◽  
Surface Waves ◽  
Scaling Laws ◽  
Similarity Theory ◽  
Vertical Mixing ◽  
Temperature Gradients ◽  
Langmuir Turbulence ◽  
Near Surface ◽  
Oceanic Surface ◽  
Using Data

AbstractMonin-Obukhov Similarity Theory (MOST) provides important scaling laws for flow properties in the surface layer of the atmosphere and has contributed to most of our understanding of the near-surface turbulence. The prediction of near-surface vertical mixing in most operational ocean models is largely built upon this theory. However, the validity of MOST in the upper ocean is questionable due to the demonstrated importance of surface waves in the region. Here we examine the validity of MOST in the statically unstable oceanic surface layer, using data collected from two open ocean sites with different wave conditions. The observed vertical temperature gradients are found to be about half of those predicted by MOST. We hypothesize this is attributable to either the breaking of surface waves, or Langmuir turbulence generated by the wave-current interaction. Existing turbulence closure models for surface wave breaking and for Langmuir turbulence are simplified to test these two hypotheses. Although both models predict reduced temperature gradients, the simplified Langmuir turbulence model matches observations more closely, when appropriately tuned.

scholarly journals Horizontal Wave Number Dependence of Type II Solutions in Rayleigh?Benard Convection with Hexagonal Planform

1984 ◽  
Vol 37 (5) ◽  
pp. 531 ◽  
Author(s):  
JM Lopez ◽  
JO Murphy
Keyword(s):  
Vertical Component ◽  
Wave Number ◽  
Type I ◽  
Type Ii ◽  
Horizontal Wave ◽  
Convection Problem ◽  
Parameter Values ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard ◽  
Cyclonic Type

The horizontal wave number dependence of the hexagonal planform solutions for the RayleighBenard convection problem, which have a nonzero vertical component of vorticity (type II solutions), has been established. Over the range of wave numbers which support cellular convection, comparisons between the thermal transport characteristics of these cyclonic type solutions and those traditionally obtained from nonlinear investigations of the single horizontal mode equations (type I solutions) have been made. From the numerical results obtained, it is found that the cell aspect ratio which maximizes the heat flux of type II solutions is larger than that for type I solutions, at quivalent parameter values, and that the value of the horizontal wave number giving maximum Nusselt number for type II solutions increases with Rayleigh number and decreases with Prandtl number.

Band Gap Formation by Cylinder Arrays in an Acoustic Waveguide

2007 ◽  
Author(s):  
Liang-Wu Cai ◽  
David C. Calvo ◽  
Dalcio K. Dacol ◽  
Gregory J. Orris
Keyword(s):  
Acoustic Waves ◽  
Stop Band ◽  
Three Dimensional ◽  
Wave Number ◽  
Pass Band ◽  
Gap Formation ◽  
Numerical Examples ◽  
Cylinder Arrays ◽  
Horizontal Wave ◽  
Special Case

Scattering of acoustic waves by arrays of identical circular cylindrical scatterers in a horizontal waveguide is studied. Although three-dimensional in its geometry, the waveguide permits only a finite number of modes of acoustic wave propagating in different directions with respect to horizontal, and the number of these propagating modes increases as the frequency increases. The horizontal wave numbers of these modes span a range of frequency limited by the total wave number. Numerical examples are used to explore a special case in which the cylinder height equals the depth of the waveguide and in which the cylinders and the waveguide have pressure-release boundaries at both top and bottom surfaces. In such a special case, there is no coupling among the modes permitted by the waveguide and hence is the simplest case for such problems. It is observed that the combination of the modes generally decreases the wave-blocking effects of a stop band; and it is likely that a stop band in one waveguide mode might correspond to a pass band in a different mode. However, numerical examples also show that the main characteristics of a stop band are maintained, despite the multiple modes; and it is possible to extend the stop band by cascading cylinders arrays of different arrangement.

The Influence of the Rayleigh and Prandtl Numbers on Convective Heat Transport in Stars

1980 ◽  
Vol 4 (1) ◽  
pp. 39-41
Author(s):  
J. O. Murphy
Keyword(s):  
Coefficient Of Thermal Expansion ◽  
Fluid Layer ◽  
Wave Number ◽  
Marginal Stability ◽  
Convection Cell ◽  
Horizontal Scale ◽  
Convective Processes ◽  
Horizontal Wave ◽  
Unstable Layer ◽  
Prandtl Numbers

The two important parameters which essentially determine the nature of the convective regime, and consequently the total heat transported by convective processes, across an unstable layer in a star are the Rayleigh and Prandtl numbers defined by (Chandrasekhar 1961)where ν is the coefficient of kinematic viscosity, x is the coefficient of thermal diffusivity and α, g, d, ΔT are respectively the coefficient of thermal expansion, acceleration due to gravity, depth of the fluid layer and temperature difference across the layer. In addition, the horizontal scale of the convection cell is determined by the horizontal wave number a and for convection to be established R must be greater than the critical value at marginal stability, Rc, which is a function of a, given bywhen the free boundary conditions apply.

scholarly journals Time Variation of Velocity Flows from Ring Diagrams: A First Approach

1998 ◽  
Vol 185 ◽  
pp. 175-176
Author(s):  
J. Patrón ◽  
I. González Hernández ◽  
D.-Y. Chou ◽  
Keyword(s):  
Temporal Frequency ◽  
Power Spectra ◽  
Temporal Variations ◽  
Three Dimensions ◽  
Wave Number ◽  
Local Analysis ◽  
The Sun ◽  
Ring Diagram ◽  
Analysis Technique ◽  
Horizontal Wave

The Ring Diagram analysis is a technique designed to infer the presence of horizontal velocity flows under the solar surface by the analysis of the power spectra of solar oscillations in three dimensions: the two components of the horizontal wave number and temporal frequency (Hill, 1988 and Patrón et al., 1995). This procedure is applied as a local analysis technique, performed for a region of the Sun of several heliographic degrees (typically around 15×15 degrees square). As the Sun is rotating, we must track a chosen region as long as it is present at the visible part of the solar disk, and we can continue the tracking after several solar rotations. The comparison of the estimated flow fields obtained at different times can give some ideas about the temporal variations of the flows.

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