摘要:

A theory of the general circulation which admits mid-ocean fronts is examined. This study is related to some earlier studies of two layer planetary geostrophic systems, where it was argued that interior discontinuities, or “fronts”, generally arise as a result of the nonlinearity in the continuity equation. Similar dynamics are studied here under more general circumstances. It is argued that the most general solution for the interior thermocline requires several fronts, each of which arises in response to a mismatch of subsurface potential vorticity structure on isopycnals. Further, these fronts can influence each other and determine large areas of the basin scale potential vorticity field. Comparisons between special analytical solutions and numerical solutions are made. The main result of this work is that the frontogenisis in planetary geostrophic dynamics is robust, characteristic of highly stratified systems and of potential importance to basin scale structure.

ISSN:0309-1929    

DOI:10.1080/03091929408203630

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We study a class of vortex dipoles consisting of two patches of uniform potential vorticity in an otherwise quiescent flow on a β-plane. Steadily propagating solutions that are desingularised analogues of point vortex dipoles are found and compared with the point vortex solutions. Like the point vortex dipoles, both rapidly and slowly propagating solutions exist. Numerical simulations show that the slow solutions are unstable and break up under the influence of weak external perturbations. The fast solutions are more robust. The minimum dipole strength necessary for the existence of a steadily propagating solution is less than that found for point vortex dipoles.

ISSN:0309-1929    

DOI:10.1080/03091929408203631

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Modon solutions of the equivalent barotropic vorticity equation on a sphere with a horizontal shear in the zonal background flow are presented. These solutions are wavelike tripoles that exist in the presence of a prescribed shear term quadratic in the sine of the latitude. The sphere is divided into an inner and outer region separated by a boundary circle, and different linear relationships between potential vorticity and stream function in a comoving frame are assumed for the two regions. There are two constraints on the wavenumbers of the solutions in the inner and the outer region, the radius of the circle, and the strength of the prescribed shear. The strength of the prescribed shear determines the latitude of the jet and the strength of the tripole. These solutions are compared with earlier results for equivalent barotropic modons on the beta plane.

ISSN:0309-1929    

DOI:10.1080/03091929408203632

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Using a nonlinear critical layer analysis, we find a class of steady state, finite-amplitude waves in the Garcia model of an inviscid stratified shear layer. The vorticity distribution inside the vortex cores is similar to that of the family of two-dimensional vortices, known as Stuart vortices, found by Stuart (1967) in a homogeneous shear layer. The solutions obtained are compared with those previously obtained using similar techniques, but for which the Prandtl-Batchelor theorem had been invoked inside closed streamlines to justify the homogenization of vorticity therein.

ISSN:0309-1929    

DOI:10.1080/03091929408203633

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The formation of a steady quasi-geostrophic flow component over undulating bottom variations is analysed in the case when wave-topography interactions dominate over nonlinear wave-wave couplings. A low-order model is proposed to describe quasi-linear dynamics and our main attention focusses on the qualitative structures of two functions: the correlation between relative vorticity and topography (C) and a topographic stress force (D).Cturns out to be both positive and negative depending on the parameters of an incident wave and topography mode, and on the dissipation mechanism taken into account. The β-effect increasesCand isotropy of the dynamical wavy field or that of the topography decreases this quantity.

ISSN:0309-1929    

DOI:10.1080/03091929408203634

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We use a 2-dimensional non-hydrostatic model on the vertical plane to examine the nature of convective adjustment. In the first part of the study, we investigate the mixing of an initial unstably stratified 2-layer fluid with molecular viscosities. The linear growth rates compare well to those obtained using an analytic model. The stratification of the convectively adjusted state is sensitive to the Prandtl number (Pr, the ratio of the eddy viscosity to thermal diffusivity). This is important as the instantaneous convective adjustment used in coarse resolution ocean circulation models corresponds toPr→0, while the case of immiscible fluids corresponds to the limit of largePr.Mixing in the ocean as well as in our numerical model are both characterized by a finite value ofPr.In the second part of the study, we scale up to ocean scales with a more realistic surface forcing and turbulent viscosities. The implications of our results for instantaneous convective adjustment are discussed.

ISSN:0309-1929    

DOI:10.1080/03091929408203635

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Experiments on modelling of vortex structures occurring in a rotating fluid have been carried out. It has been proved that a differential rotation depends on a convection regime. It is supposed that the structures, studied on the models, are analogous to those occurring in the convective zone of the Sun and planet liquid-metal core.

ISSN:0309-1929    

DOI:10.1080/03091929408203636

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Thermal convection in rapidly rotating systems is investigated numerically with self-gravitating spherical shells, within Boussinesq approximation, with the radius of the inner sphere η = 0.4 relative to that of the outer sphere. Marginal convection experiences a series of metamorphoses with decreasing Prandtl number: from the columnar mode to the spiralling mode, and then to the wall-attached mode. The physical processes of the metamorphses are clarified by diagnosing both the vorticity and the thermodynamic balances.

ISSN:0309-1929    

DOI:10.1080/03091929408203637

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0309-1929    

DOI:10.1080/03091929408203638

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The statistical behavior of time series of reversals (TSR) of the Geomagnetic field is studied. It is demonstrated that TSR possess the self-similarity property under time scale transformations. The authors believe that such a simple statistical property should be a consequence of the unique physical mechanism leading to the reversals, and it is not necessary to find special reasons for the explanation of the long and short time intervals between them. To test this idea, TSR were analysed which result from various models of the Geomagnetic field. Simplest models like the well-known Rikitake model do not exhibit self-similarity properties despite the fact that their TSR show statistical behavior. More realistic models with significantly larger number of degrees of freedom (e.g. Hollerbachet al., 1992) really demonstrate such self-similarity properties.

ISSN:0309-1929    

DOI:10.1080/03091929408203639

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor