摘要:

The model ocean has an active upper layer driven by surface wind stress and surface heating on time scales of one to ten years. The deep passive mixed lower layer redistributes cold water from polar regions to the sub-tropical ocean. The dynamics of the upper layer are represented by the reduced gravity equations modified to allow interaction between the two layers by deep upwelling and entrainment at the interface. There is deep upwelling and entrainment at the bottom of the mixed layer. A selection of different distributions of surface wind stress and surface heating are used to drive the circulation including slowly moving wind bands, and slow changes of surface heating.

ISSN:0309-1929    

DOI:10.1080/03091929508229761

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper examines large-scale (in the sense of small Rossby number) wind and buoyancy driven ocean circulation in a thermodynamic single active layer reduced gravity model. It is proved that in a closed domain bounded by a piecewise orientable boundary there are an infinite number of steady state solutions for a given wind stress.

ISSN:0309-1929    

DOI:10.1080/03091929508229762

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new technique is presented for the efficient time-integration of the equations that describe the slow deformation in the Earth's mantle. This method is based on the adaptive, high order implicit solver for differential-algebraic equations (DASPK) and is independent of the choice of spatial discretization technique. Using a standard finite element package for the spatial discretization, it is shown that the solution of the 2-D convection-diffusion equation for temperature can be performed at much lower computational cost, but at the same or higher accuracy, compared to a traditional implicit second-order method. The solution to the full set of 2-D mantle convection equations is 3 to 4 times more efficient. Both in 2-D and 3-D, the memory and CPU-usage of this implementation depends linearly on the number of grid points and has good properties with respect to vectorization and parallelization. As an application of this technique, convection in the Earth's mantle with strongly temperature and pressure dependent rheology is studied in axisymmetric geometry. Models are developed that are consistent with current estimates of surface heat flow and radial viscosity distribution. General characteristics are: a dynamic upper mantle overlying a near-stationary lower mantle; strong plumes rising from the core-mantle boundary, even at high rates of internal heating; and an effective Rayleigh number of nearly two orders of magnitudes lower than commonly used values in the range of 107to 108.

ISSN:0309-1929    

DOI:10.1080/03091929508229763

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this paper we investigate the stationary thermoconvective instability of a rotating fluid layer with a deformable free surface. In order to understand phenomena which could appear in planetary and stellar systems, a variety of mechanical and thermal boundary conditions is considered, which give upper and lower stability bounds to all possible physical situations. It is shown that rotation is stabilizing when surface deformation is present, for large values ofG[sgrave], the product of the Galileo and Prandtl numbers, which appears due to surface deflection. Moreover, it is shown that for certain boundary conditions the interaction between rotation and gravity through surface deformation leads to an increase in convection cell size (decrease in wavenumber) and destabilization of the system when the Taylor numberTaincreases andG[sgrave] is relatively small. The Boussinesq approximation is violated when infinite size convection cells appear in our analysis. Therefore, graphs of the critical values ofG[sgrave] andTacorresponding to the limits of this approximation are given along with analytical expressions for the corresponding Rayleigh numbers.

ISSN:0309-1929    

DOI:10.1080/03091929508229764

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Resistive-MHD winds from strongly magnetized, rapidly rotating stars are examined semi-analytically. The basic equations are reduced by assuming that the plasma surrounding a central star forms a thin disk around the equatorial plane owing to the action of centrifugal force.

ISSN:0309-1929    

DOI:10.1080/03091929508229765

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

For party-symmetric flows of the formvr(r, t)1r+vhwherevhis an arbitrary horizontal (non-radial) component andris the spherical radius, in a spherical electrically conducting fluid volume the evolution of the poloidal magnetic field decouples from the toroidal magnetic field. It is shown that flows of this class cannot maintain poloidal magnetic fields against ohmic decay. Specifically,, whereS(r) is the spherical surface of radiusrconcentric with the origin andBis the magnetic induction, is shown to decay to zero monotonically and unconditionally. The proof uses a comparison theorem, established by maximum principles for one dimensional parabolic inequalities, to construct comparison function bounds, one of which decays to zero, on the absolute magnetic flux through. The result strengthens the antidynamo theorem of Ivers and James (1988) for partly-symmetric flows by relaxing the incompressibility ofvh.

ISSN:0309-1929    

DOI:10.1080/03091929508229766

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The paper presents evidence that a kinematic dynamo with a purely poloidal magnetic field does not exist. In particular, it is shown that the poloidal scalarS, if it satisfies a certain regularity condition, decays monotonically with respect to the norm maxz(maxx, yS—minx, yS) in the case of a plane fluid layer and with respect to the norm maxr[r(max|r|=rS—min|r|=rS)] in the case of a spherical fluid volume. The result is valid for nonsteady, radially varying conductivity, possibly moving boundaries and a nonsteady, compressible flow field constrained in such a way that no toroidal magnetic field is generated. Similar decay results apply to the nonradial derivatives ofS.Since the above norm is equivalent to the uniform max-norm, we have also (not necessarily monotonic) decay ofSin the max-norm. For steady or time-periodic flow fields these results imply exponential decay ofSand its derivatives to zero. The steady case, finally, is ruled out by application of standard maximum principles for elliptic partial differential equations.

ISSN:0309-1929    

DOI:10.1080/03091929508229767

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor