摘要:

Numerical experiments have been conducted to investigate the evolution of pure baroclinic eddies using two-layer planetary geostrophic equations in the presence of localized bottom topography. In particular, we interpret the eddy motion in terms of JEBAR (joint effect of baroclinicity and relief). It is shown that the emission of barotropic flows (or waves), westward acceleration and energy conversion occur when an eddy interacts with bottom topography. A meridional ridge acts as a repellor for a cold eddy and an attractor for warm eddy due to JEBAR-induced barotropic flows (or waves), which is consistent with the vorticity argument. This mechanism may provide a possible explanation not only for the global distribution of the phase speed of baroclinic Rossby waves observed in the Pacific by the TOPEX/POSEIDON satellite altimeter but also for the abrupt change in the trajectories of the westward propagating baroclinic eddies observed in the North Atlantic.

ISSN:0309-1929    

DOI:10.1080/03091929708208971

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Low-frequency topographic Rossby waves in continuously stratified flow propagate along both coastal shelves and seafloor ridges. Where the cross-section of the coastal shelf or ridge changes abruptly, or where a seafloor ridge abuts a coastal shelf, incident waves are scattered. This paper uses an isobath tracing result and a new, more efficient, method of calculating the wave modes to completely resolve the transmitted and reflected modes in these geometries.

ISSN:0309-1929    

DOI:10.1080/03091929708208972

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A variable-grid, high-order finite difference (FD) method is applied to the modeling of mantle convection in both two- and three-dimensional geometries. The algorithm combines extreme simplicity in programming with a very high degree of accuracy. Memory requirements are low and grow almost linearly with the total number of grid points in three dimensions, regardless of the increase in grid points in the vertical direction. Higher-order methods, such as eighth order, yield significantly better results than a second-order method for the same grid size, with only a modest increase in memory requirements. This is particularly important for high Rayleigh number convection, where the large number of grid points required to obtain an accurate enough solution with second-order schemes would make the computation extremely costly. The small-scale features in the hard-turbulent regime under high-Rayleigh number situations can greatly stress low-order methods, and in these situations a high-order method is definitely needed. We have numerically simulated three-dimensional time-dependent convection for constant properties up toRa= 108, using an eighth-order FD scheme. Both purely base-heated and partially internally heated situations have been considered. The hot plumes are broader near the surface with internal heating. Detailed studies of the three-dimensional constant viscosity plumes indicate that no small-scale circulation takes place in the ascending plume heads regardless of the heating configuration in accordance with predictions from boundary layer theory.

ISSN:0309-1929    

DOI:10.1080/03091929708208973

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Anufrievet al.(1995) have recently presented a mean field geodynamo model in which the magnetic field appears to scale as B = O(E1/8), where the Ekman numberEis a measure of viscous to Coriolis forces. They called these new solutions semi-Taylor states, as they seem to be intermediate between Ekman states having B = O(E1/4) and true Taylor states having B = O(1), both familiar in the literature. I present a balance which will yield precisely such an O(E1/8) scaling, and in the process demonstrate that this is indeed the only intermediate state one may have. I suggest how one might reconsider this particular solution of Anufrievet al., in light of this balance. Finally, I discuss the possible geophysical implications of these new solutions.

ISSN:0309-1929    

DOI:10.1080/03091929708208974

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

First the exact numerical solutions of DIA system of equations describing the transportation of magnetic field in an infinite medium are presented. It is assumed that the turbulence is stationary, homogeneous, isotropic and incompressible. The spectra of turbulence of δ-type and Kolmogorov's type were used. The steady state values of magnetic field diffusivityDTand the α-effect coefficient αTwere calculated for various values of space-scale and lifetimes of these spectra and the spectra of helicity. Also investigated is the dependence ofDTand αTon the degree of helicity. The corrections to the αT-coefficient due to the contribution of four-order velocity correlators are given. The results are compared with those due to the self-consistent technique.

ISSN:0309-1929    

DOI:10.1080/03091929708208975

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In order to understand the topology of complex flux systems we analyse in detail the rich structural properties of the magnetic field created in turn by two or three balanced or unbalanced flux sources. Passing through each three-dimensional magnetic null point (where the field vanishes) is an isolated spine field line and a flux surface known as a fan. The fans form separatrix surfaces which separate the volume into topologically distinct regions and generally intersect each other in separator field lines linking pairs of null points. Furthermore, the fan of one null can terminate at the spine of another null, whilst the spine terminates either at a source or at infinity. The skeleton of complex three-dimensional magnetic fields therefore comprises the magnetic null points and a network of spine curves and separatrix fan surfaces. The skeletons due to three sources are classified and found to be surprisingly complex. For example, a new discovery is that a configuration with a separator may be produced by only three sources.

ISSN:0309-1929    

DOI:10.1080/03091929708208976

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor