摘要:

Sufficient conditions for stability are established for the magnetic field problem of the Earth's core considered by Braginsky.

ISSN:0309-1929    

DOI:10.1080/03091927708242324

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0309-1929    

DOI:10.1080/03091927708242325

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The evolution of a Rossby wave forced on a uniform shear is considered, the strength of the wave being characterised by a parameter ε ≪ 1. In the first stage of the process, whent∼ 1, a steady flow is established everywhere outside a layer near the line y = 0, known as the critical layer, in which the vorticity oscillates with increasing amplitude. The velocity jump across the layer is however steady and of the same wavelength as the forcing oscillation. At larger times (ε1/2t∼ 1) the velocity jump oscillates slowly and higher harmonics are generated. It is shown by considering a model equation that as ε1/2t→ ∞ the velocity jump tends to zero but that violent oscillations in the velocity normal to the layer are induced. The relation of this theory with the Benney-Bergeron-Davis theory is discussed and the effect of viscosity briefly considered.

ISSN:0309-1929    

DOI:10.1080/03091927708242326

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Observations are reported on the stability and structure of Rayleigh-Benard convection in a fluid with a Prandtl number of 8,600, and Rayleigh numbers between 50,000 and 760,000. Under carefully initiated and controlled conditions, stationary bimodal convection was observed, even at the highest Rayleigh number. Unstable bimodal patterns broke down in a way that tends to reduce the wavelength of the cells. Oscillating spoke-shaped convection was observed in convection started from random initial conditions. The gradual increase in the occurrence of oscillations and the dependence on the initial conditions probably accounts for previous disagreements about the onset of time dependence. A square convection planform was found which was stable at the highest Rayleigh numbers but unstable for lower Rayleigh numbers. The observations demonstrate the existence of different possible solutions at a given Rayleigh number.

ISSN:0309-1929    

DOI:10.1080/03091927708242327

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Non-divergent barotropic shelf waves on the Ghanaian Continental shelf (5°N) are examined using both a β -plane and anf-plane model. The results agree to within 10% and indicate that the observed 71/2day and 10 day oscillations in sea level are manifestations of the first two barotropic shelf wave modes.

ISSN:0309-1929    

DOI:10.1080/03091927708242328

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The possible interaction of trapped midoceanic boundary waves with a nearby coastline is examined by considering a step trench-ridge topography adjoining a semi-infinite straight coastline. The full dispersion equation, including the effect of the earth's rotation, is derived for long waves over this topography. It is shown that the presence of the coastline begins to have a significant effect on the behaviour of quasigeostrophic ridge waves whenever the wave length is greater than three times the ridge coastline separation.

ISSN:0309-1929    

DOI:10.1080/03091927708242329

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The observed surface angular velocity of main-sequence stars shows a sharp decrease at about spectral type F6. We suggest that stars more massive than F6 cannot experience an appreciable angular momentum loss because their convection zones cannot sustain a magnetic dynamo: without a magnetic field the angular momentum loss is very small. The influence of rotation on the convective motions is essential for the existence of a solar type dynamo. Rotation can influence these convective motions only if the typical convective time is larger than the rotation time, i.e., ifl/uc> 1/Ω, whereucandlare typical values of the convective velocity and mixing length in the lower part of the convection zone and Ω is the star's angular velocity. For main-sequence stars of different masses and chemical compositions we evaluate the dimensionless parameteruc/Ω⊙land show that it increases very sharply for stars whose mass, M, exceeds that defined bylog(M /M⊙) ≑ 0.1 (Ω⊙, and M⊙, are the sun's angular velocity and mass, respectively). Thus even for large angular velocities, magnetic dynamos are not feasible if log(M/M⊙) appreciably exceeds 0.1.

ISSN:0309-1929    

DOI:10.1080/03091927708242330

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Models of a convectively driven hydromagnetic dynamo are constructed using a truncated modal expansion. The resulting nonlinear partial differential equations are integrated numerically. The results confirm that rotation is a necessary condition for effective dynamo action, and suggest that equipartition of kinetic and magnetic energies is qualitatively valid, and that toroidal field energies can be much larger than poloidal.

ISSN:0309-1929    

DOI:10.1080/03091927708242331

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The model of Anufriyev and Braginskii (1975) and Moffatt and Dillon (1976) is further studied, with a view to calculating (i) the mean tangential stress on the core-mantle interface, and (ii) the level of the α-effect due to flow over the surface bumps. The stress calculated agrees in order of magnitude with the stress of 0.04 Nm−2that is inferred from the decade variations in the length of the day.

ISSN:0309-1929    

DOI:10.1080/03091927708242332

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Braginsky (1963) has suggested that the geodynamo is gravitationally powered through the settling downwards of the heavy iron-rich component in the fluid outer core to form a growing solid inner core. Supposing for simplicity that the core is a binary alloy, we examine implications of Braginsky's idea and, in particular, discuss the importance of slurry layers in the fluid core. A thermodynamically acceptable theory for the motion of a slurry is developed, and approximations that make it tractable are discussed. The structure of a well-mixed slurry layer is elucidated. The theory is used to show how seismic waves traversing a slurry are damped and dispersed as a result of melting and re-freezing of the solid phase caused by the passage of the wave.

ISSN:0309-1929    

DOI:10.1080/03091927708242333

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor