摘要:

A principal mechanism in the spin-up from rest of a stratified fluid is the development of intense penetrative vortices produced by flow instabilities. The main features of this process are described.

ISSN:0309-1929    

DOI:10.1080/03091928008241167

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The linear stability analysis of Hathaway, Gilman and Toomre (1979) (hereafter referred to as Paper I) is repeated for Boussinesq fluids with viscous and thermal diffusion. As in Paper I the fluid is confined between plane parallel boundaries and the rotation vector is oblique to gravity. This tilted rotation vector introduces a preference for roll-like disturbances whose axes are oriented north-south; the preference is particularly strong in the equatorial region. The presence of a latitudinal temperature gradient produces a thermal wind shear which favors axisymmetric convective rolls if the gradient exceeds some critical value. For vanishingly small diffusivities the value of this transition temperature gradient approaches the inviscid value found in Paper I. For larger diffusivities larger gradients are required particularly in the high latitudes. These results are largely independent of the Prandtl number. Diffusion tends to stabilize the large wavenumber rolls with the result that a unique wavenumber can be found at which the growth rate is maximized. These preferred rolls have widths comparable to the depth of the layer and tend to be broader near the equator. The axisymmetric rolls are similar in many respects to the cloud bands on Jupiter provided they extend to a depth of about 15,000 km.

ISSN:0309-1929    

DOI:10.1080/03091928008241168

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Assuming there is a separation in scale between the mean flow and fluctuations, the linearized potential vorticity equation is solved using the WKB method. Attention is focused on wave properties such as action and enstrophy which in some circumstances are conserved. In the most general case of Rossby waves supported by an arbitrary mean potential vorticity field,q=f/h, and propagating through a forced mean flow neither action nor enstrophy is conserved. It is shown that action is produced by the forcing which drives mean flow acrossqcontours, while enstrophy is produced both by complicatedqcontours and by horizontal divergence of the mean flow.

ISSN:0309-1929    

DOI:10.1080/03091928008241169

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The barotropic vorticity equation in the presence of time-dependent localized external excitation is investigated using the weakly nonlinear approach. Conditions for linear and nonlinear resonance are found. Under certain conditions steady rectified currents can be excited yielding an effectively steady state response to time-dependent excitation. The applicability of the results to the blocking phenomenon is discussed.

ISSN:0309-1929    

DOI:10.1080/03091928008241170

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Finite amplitude, axisymmetric, steady convective motions of an infinite Prandtl number, Boussinesq fluid in a spherical shell are computed using a Galerkin technique. Two types of heating are considered. In one case, convection is driven both by internal heat sources in the fluid and by an externally imposed temperature drop across the boundaries of the shell. In the other case, only internal heat sources drive convection and the lower boundary of the shell is adiabatic. The boundaries of the shell are stress free. When heating is both from below and from within, the lower boundary is isothermal. The upper boundary is isothermal for both types of heating. The radial gravitational field is spherically symmetric and the local acceleration of gravity is directly proportional to radial position in the shell, as is appropriate to a sphere of constant density. Only the case of a shell whose outer radius is twice its inner radius is considered. Two distinct classes of axisymmetric steady states are possible. The temperature and radial velocity fields of solutions we refer to as “even” are symmetric about an equatorial plane, while the latitudinal velocity is antisymmetric about this plane; solutions we refer to as “general” do not possess any symmetry properties about the equatorial plane. The characteristics of these solutions, i.e. the isotherms, streamlines, spherically averaged temperature profiles, Nusselt numbers, etc., are given for Rayleigh numbers ranging from the critical value for the onset of convection to several times this value. Linear stability analyses of the nonlinear axisymmetric steady states show, when heating is both from below and from within, that near the onset of convection, a fully three-dimensional general motion is preferred, while at higher Rayleigh numbers, axisymmetric steady general motions are both preferred over axisymmetric steady even motions and stable against nonaxisymmetric perturbations. When heating is strictly from within and the lower boundary is adiabatic, the only possible steady motions are fully three-dimensional, i.e. all steady axisymmetric solutions are unstable to azimuthal perturbations.

ISSN:0309-1929    

DOI:10.1080/03091928008241171

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A one-dimensional energy-balance equation involving diffusive energy transport and taking into account the ice-albedo feedback is considered. A systematic elimination of the spatial degrees of freedom is performed. This gives rise to a zero-dimensional climate model displaying the explicit dependence of planetary albedo on planetary temperature and on some model parameters. In the general case, the zero-dimensional model involves memory effects as well as two characteristic relaxation rates.

ISSN:0309-1929    

DOI:10.1080/03091928008241172

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A hydrostatic tidal model is presented which can successfully account for the two major features of lunar asymmetry. These are the observed offset between the centre of figure and the centre of mass, and the preferential distribution of lunar maria on the earthward side of the moon. The model requires that the following three processes occurred at the Roche stability limit: (a) formation, (b) petrological differentiation to give a mantle and an approximately 100 km thick crust, and (c) rigidification of the distorted mantle. We further demand that the mantle-crust boundary retain its distorted shape over the subsequent recession of the moon from the earth. Persistence of this distortion on a time scale of the order of one billion years can only occur if the upper mantle has a very high viscosity: this may be a physically implausible requirement. An extension of this model to consider the influence of asymmetric tides on crystal-liquid differentiation in a converting moon remains open for exploration.

ISSN:0309-1929    

DOI:10.1080/03091928008241173

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

This study uses σ-stability analysis to explore the hydromagnetic instabilities of a star with an axisymmetric toroidal magnetic field. Necessary and sufficient conditions for σ-stability are derived and are used to obtain the maximum growth rate (MGR) of instability. The concepts determining the point of MGR and the σ-stability line are introduced as rigorous tools to investigate the instabilities.

ISSN:0309-1929    

DOI:10.1080/03091928008241174

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The Cowling anti-dynamo theorem is proved using the Bullard and Gellman spectral formulation of kinematic dynamo theory.

ISSN:0309-1929    

DOI:10.1080/03091928008241175

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

By W. Unno, Y. Osaki, H. Ando, H. Shibahashi, University of Tokyo Press, 344 pp., Y5800 ($32.50, £16.50). (ISBN 0-86008-258-X) 1979.

ISSN:0309-1929    

DOI:10.1080/03091928008241176

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor