摘要:

The parameter ranges relevant to propagating oceanic eddies are explored with a view to simplifying the equation sets previously used to simulate such eddies. The reduced gravity shallow-water model is used as a starting point. We consider eddies whose width is of the same order as, or somewhat larger than, the Rossby deformation radius. Two model equations emerge from these scalings, both permitting modon solutions and easy numerical integration. Both, too, give fair simulations of the shallow-water model, but disagree in details.

ISSN:0309-1929    

DOI:10.1080/03091928708210109

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The process of wave steepening in Long's model of steady, two-dimensional stably stratified flow over orography is examined. Under conditions of the long-wave approximation, and constant values of the background static stability and basic flow, Long's equation is cast into the form of a nonlinear advection equation. Spectral properties of this latter equation, which could be useful for the interpretation of data analyses under mountain wave conditions, are presented. The principal features, that apply at the onset of convective instability (density constant with height), are:

ISSN:0309-1929    

DOI:10.1080/03091928708210110

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

It is shown that compressible convective motions in a density-stratified rotating fluid give rise to non-diffusive fluxes of the angular momentum (Λ-effect), thus leading to differential rotation. This also occurs for the case of extremely small convection anisotropy. Attention is focused on this case of quasi-isotropic convection and the Λ-effect of quasi-isotropic convection is derived. The corresponding fluxes of the angular momentum, as well as the resulting deviation of the rotation from homogeneity, are shown to be proportional to the second spatial derivative of the fluid density squared. The solution of the Reynolds equation is found for a particular density profile. Isorotational surfaces corresponding to different values of the Rossby number,Ro, are considered. The angular velocity increases with depth and towards the equator whenRo≾0.3which corresponds to the middle and lower parts of the solar convection zone. The results obtained are compared with observations. A possible physical picture of the differential rotation set up by compressible convection is suggested.

ISSN:0309-1929    

DOI:10.1080/03091928708210111

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

In an earlier paper (Fearn and Proctor, 1984) we described results from a preliminary model of a spherical hydromagnetic dynamo driven by convection. An iterative approach was used. Starting from some guess for the mean toroidal field Bwe solved for the form of the convective instability in the presence of this field. The mean e.m.f. E [defined in (2.13)] associated with the convection was calculated, and from this, anα-effect was constructed (α=EΦ/B). We then solved a mean fieldαΩ-dynamo model to produce a new “B”. This cycle was repeated untilBconverged. For a preliminary investigation, there were good reasons for using anα-effect formalism. However, a more straightforward and physically more realistic approach is to use the e.m.f.EΦdirectlyto force the mean field dynamo. This “EΩ-dynamo” is used here. The converged results of Fearn and Proctor (1984) are successfully reproduced and in addition we have found converged steady dynamos in the absence of any poloidal flow (cf. Roberts, 1972). Our iterative dynamo is still far from being completely self-consistent since several parameters and the mean fluid flow have had to be arbitrarily prescribed. The next step is to incorporate more of the dynamics. We use the mean momentum equation to determine the mean flow and, in particular, apply Taylor's (1963) constraint to determine the otherwise arbitrary geostrophic flowUG(s)TheEΩ-dynamo permits this to be done with relative ease (see Fearn and Proctor, 1987). No converged results were found. Solutions either became too detailed to resolve, magnetic instabilities became present, or the solution jumped between two different modes of convection.

ISSN:0309-1929    

DOI:10.1080/03091928708210112

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

This paper describes a re-investigation of the geomagnetic dynamo model proposed by Braginsky (1978). This axisymmetric nonlinear model was dominated by Lorentz and Coriolis forces, and was maintained by a specified thermal wind and by a specifiedα-effect. Of particular interest were the strong indications of non-uniform behavior in the limit of small core-mantle coupling. The solution did not seem to approach a form independent of that coupling as had been suggested by Taylor (1963), but developed a model-Z structure as had been proposed by Braginsky (1975). In view of the significance of this result to dynamo theory, his integrations were repeated at higher resolution, with the results described in this paper. Apart from a few minor differences, Braginsky's findings were confirmed. Other integrations also gave dynamos of model-Z structure.

ISSN:0309-1929    

DOI:10.1080/03091928708210113

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

by Ghislain de Marsily, Academic Press, vii+440 pp. U.S. $29.95 (ISBN 0-12-208916-2) 1986.

ISSN:0309-1929    

DOI:10.1080/03091928708210114

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

by M. T. Landahl and E. Mollo-Christensen, Cambridge University Press, vi+154 pp., †34.50 (ISBN (0-521-26306-9) 1986.

ISSN:0309-1929    

DOI:10.1080/03091928708210115

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor