摘要:

The propagation of Alfvén waves along a uniform horizontal field in a highly conducting incompressible fluid, subject to the convective forces produced by a uniform vertical temperature gradient, is treated in a Boussinesq approximation. It is shown that there are exact solutions with large amplitude but restricted form. Their restricted form means that an arbitrary disturbing force produces other motions as well as Alfvén waves. An arbitrary initial disturbance of small amplitude produces waves whose state of polarization varies along the direction of propagation. For large amplitudes, however, any mixtures of polarization states causes scattering into new modes.

ISSN:0309-1929    

DOI:10.1080/03091928408248179

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

High resolution numerical simulations extending those of Arnold and Korkina (1983) reveal the existence of at least two windows for kinematic dynamo action in a spatially periodic flow with chaotic streamlines. These occur at moderate magnetic Reynolds number R (8–18) and at high R (27 to 200 or more).

ISSN:0309-1929    

DOI:10.1080/03091928408248180

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Magneto-Boussinesq approximation is derived as a set of leading order equations in an asymptotic expansion. An analogous set of equations is derived for the case when the Alfvén speed is comparable to the sound speed.

ISSN:0309-1929    

DOI:10.1080/03091928408248181

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A vortex-tube geometry of the cascade of energy to small-scale eddies, in the inertial range of fully-developed turbulence, is proposed. The model is a special case of the beta model of Frisch, Sulem and Nelkin (1978). We require that the cascade conserve the principal invariants of inviscid, incompressible flow, namely volume, topological knottedness, circulation, and, at discrete times marking the termination of steps in the cascade, energy. The process terminates in a finite time, as in any beta model, leaving behind a self-similar network of “inactive” tubes. We associate a self-similar scaling dimensionDwith the structure, equal to the Hausdorff dimension of the set of “active” tubes at the termination of the cascade. Because circulation Λ plays a key role in the analysis of the cascade, we refer to these vortex-tube geometries as “gamma models”. The viewpoint throughout is entirely deterministic.

ISSN:0309-1929    

DOI:10.1080/03091928408248182

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Finite-difference numerical solutions were obtained to present the flow and temperature field details within the transient Ekman layer during spin-up of a thermally stratified fluid in a cylinder. This complements the earlier studies on stratified spin-up which examined the flows in the interior core region. As the stratification increases, the following changes in the flow field are noticeable. The radial velocity in the Ekman layer decreases in magnitude. The azimuthal flows adjust smoothly from the interior region to the endwall boundary, and the Ekman layer in the azimuthal flow field fades. Vertical motions are inhibited, resulting in a weakened Ekman pumping. The axial vorticity field behaves similarly to the azimuthal flows. The temperature deviation from the equilibrium profile decreases, and the heat transfer flux from the endwall to the fluid decreases. The thickness of the thermal layer is larger than the velocity layer thickness. Illustrative comparisons of the relative sizes of the terms in the governing equations are conducted in order to assess the stratification effect in the adjustment process of the fluid.

ISSN:0309-1929    

DOI:10.1080/03091928408248183

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The stability of a zonal shear flow to symmetric baroclinic perturbations is examined when the Ekman number,E, is asymptotically small. It is assumed, following Antar and Fowlis (1982), that the zonal Row is generated by imposing a constant horizontal temperature gradient γ* at the horizontal boundaries, and by maintaining a constant temperature difference δT* between them. The boundaries are at rest relative to a rotating frame.

ISSN:0309-1929    

DOI:10.1080/03091928408248184

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Unbounded stratified plane Couette flow is shown to be stable against small amplitude disturbances. The Brunt-Väisälä frequency is assumed to be constant. Both viscosity and thermal diffusion are included, and shown to be stabilizing.

ISSN:0309-1929    

DOI:10.1080/03091928408248185

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Theoretical studies predict a parametric instability of finite-amplitude internal gravity waves which hitherto has been observed only in laboratory experiments. The occurrence of this process in the atmosphere is of basic interest because finite-amplitude gravity waves, which are almost ubiquitous especially at upper atmospheric heights, would produce unstable flows even at large Richardson numbers. Maximum entropy power spectra of a strong internal gravity wave in the thermosphere, which was generated by a volcanic eruption and detected on records of the Doppler shift of high-frequency radio waves, in fact show good agreement with the spectra of synthetic Doppler records obtained from a calculated unstable gravity wave. The frequencies and wavenumbers observed in the gravity wave domain satisfy in particular the theoretically predicted resonance conditions. The observed Doppler records also show two significant lines in the acoustic domain which probably result from a nonlinear interaction with the basic gravity wave. It is suggested that acoustic double peaks, which are commonly observed in high-frequency Doppler spectra in the presence of nearby thunderstorms, represent parametric instabilities of internal gravity waves generated by penetrative cumulus convection.

ISSN:0309-1929    

DOI:10.1080/03091928408248186

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

This paper describes the source-sink driven flow in a two-layer fluid confined in a rotating annulus. Light fluid is injected at the inner wall, while denser fluid is withdrawn at the outer wall. The interface between the immiscible fluids intersects the bottom and thus produces a front. The net transport from the source to the sink is carried by Ekman layers at the bottom and at the interface, and by Stewartson layers at the side walls. A detached Stewartson layer arises at the front, leading to a pronounced upwelling circulation.

ISSN:0309-1929    

DOI:10.1080/03091928408248187

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

This paper presents an analytical, two-dimensional model of the wind-induced homogeneous circulation near the edge of an ice pack floating on the ocean surface. It is shown that a vertical shear layer arises under the ice edge, by which the wind-driven geostrophic motion in the open ocean is matched to the flow region underneath the ice. As in coastal upwelling models, this shear layer consists of a thinE1/2-layer inside a thickerE1/4-layer (Ebeing the Ekman number). Under certain conditions the shear layer produces a vertical mass flux from the bottom to the surface Ekman layer. Near the surface this upwelling flux is concentrated in the narrowE1/2-layer. Comparison with observations of upwelling at the edge of a polar ice pack shows good agreement.

ISSN:0309-1929    

DOI:10.1080/03091928408248188

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor