摘要:

We examine, via direct numerical integration, the transient and rectified response of a flat-bottomed barotropic ocean to a spatially localized oscillatory wind-stress pattern. These experiments exemplify in many respects the dynamics which drive the deep motion in recent eddy-resolving ocean circulation studies [e.g., Holland and Rhines (1980)], and may be contrasted with the results of Pedlosky (1965) and Veronis (1966) for spatially broad, time-dependent forcing.

ISSN:0309-1929    

DOI:10.1080/03091928308221747

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A conducting fluid is contained in a cylindrical annulus with rigid, perfectly conducting boundaries and is permeated by a magnetic fieldB0= B0(s)ϕ (where (s,,z) are cylindrical polar coordinates). The equations governing the linear stability of this system are separable inz, and timet, and form a tenth-order boundary-value problem in s. The five conditions which must be satisfied at each boundary are u · ŝ = 0, u × ŝ=0 and e× ŝ=0 where u is the fluid velocity and e the electric field. In the limit where the cylinder is rapidly rotating about its axis, viscous effects can be neglected in the body of the fluid. The system of equations reduces to sixth order and the no-slip conditions can no longer be applied. A complication arises when waves on a timescale long compared with the rotation period are of interest, because then the equations reduce to fourth order and it is unclear what are the correct boundary conditions to be applied. A boundary-layer analysis shows that the normal magnetic field and a linear combination of the normal velocity and tangential current must vanish at the edge of the mainstream. This was checked by a numerical solution of the full, tenth-order system. The boundary condition derived is applicable when the Lorentz force is a leading order effect in the momentum equation.

ISSN:0309-1929    

DOI:10.1080/03091928308221748

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The breakdown and separation or reattachment of boundary layers adjoining a mainstream are studied in the three related situations (i)-(iii) of the title. For (i) the classical steady boundary layer generally admits a logarithmic singularity in the displacement when breakdown occurs on a downstream-moving surface whereas the corresponding singularity for an upstream-moving surface can be logarithmic or of minus-one-sixth form. Conversely, the breakdown can be delayed to the onset of zero mainstream flow, in which case the displacement singularity is again logarithmic. In certain flows these singularities prove to be removable locally, yielding a breakaway separation or reattachment and including the first known successes of a classical strategy in describing large-scale separation. Other flows, by contrast, require an interactive strategy. Again, even on a fixed surface a breakdown different from Goldstein's can be produced if there is a moving section of surface further upstream. The application to (ii), semi-similar unsteady boundary layers, e.g. near an impulsively started wedge-like trailing edge, then follows readily and predicts analogous forms of singularity. The corresponding singularity in displacement predicted for fully unsteady classical boundary layers, (iii), occurs within a finite time and, like (i) (usually) and (ii), a three-tiered breakdown is involved at first. Subsequently interaction comes into play. Comparisons with numerical and/or earlier work are noted. In all three situations (i)-(iii), although the dynamics involved near breakdown, separation or reattachment are predominantly inviscid, the presence of small viscosity is of significance in enforcing smoothness of the local velocity profiles.

ISSN:0309-1929    

DOI:10.1080/03091928308221749

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A model of the inner-core boundary (ICB) is constructed which is consistent with current ideas of the dynamic and thermodynamic state of the core and which is capable of reflecting seismic waves with period of one second. This requires the mass fraction of solid below the ICB to grow to an appreciable fraction in roughly one kilometer. This rapid growth of solid with depth is a result of downward fluid flow from the outer core which is a part of the convective motions which sustain the geodynamo. The solid which crystallizes from this descending fluid after it crosses the ICB continually coats the dendrites which occur there. The gradual cooling of the outer core causes the ICB to advance by growth of dendrites at their tips. The balance of these two effects gives an equilibrium profile for the mass fraction of solid with depth below the ICB which is capable of yielding sharp reflection of seismic waves.

ISSN:0309-1929    

DOI:10.1080/03091928308221750

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor