摘要:

When a monochromatic Rossby wave is forced on a flow which is slowly varying in time, the location of the critical line, where the phase speed of the wave is equal to that of the flow, also slowly changes. It is shown that this translation can play an important role in the vorticity balance near the critical line.

ISSN:0309-1929    

DOI:10.1080/03091928608245885

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A stratified parallel flow in a potential force field is investigated. The density, the velocity, and the potential field of the flow are allowed to vary in two directions. Three sufficient conditions are derived for guaranteed stability of the flow. Two are the classical stability conditions in their respective directions. The third, measured by a newly defined Richardson number, is a result of the shear interaction and the pressure balance condition for stability. Like the classical Richardson number which is always positive preceding stability, this new number acts as a constraint on the other two stability conditions. In addition to the above stability criteria, a semi-ellipse theorem is derived for the present flow.

ISSN:0309-1929    

DOI:10.1080/03091928608245886

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The propagation of Rossby-gravity waves, which are of astronomical interest near the critical level (or corotation point), is considered in a linear-shear, exponentially stratified flow by means of a ray tracing method. It is shown, using the analytic solutions for the stream function, that for a Richardson numberJ> 1/4 a wave-packet can cross the critical level in a finite time. In the unstable stratified case (J< 0), it cannot cross the critical level for large |J| (J< 0), but may do so for some intermediate |J| values.

ISSN:0309-1929    

DOI:10.1080/03091928608245887

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

With the help of simplifying approximations, we have derived expressions for the non-diffusive fluxes of the angular momentum which are brought about by the action of Coriolis forces on the convective motion. The original turbulence, which is not perturbed by the Coriolis forces, is considered given and weakly anisotropic, the anisotropy having a preferred radial direction. The eddy viscosities are evaluated. Hence, a closed equation for the angular velocity is derived, and then solved for the case of slow rotation. It is shown that the differential rotation is generated most effectively in the case of moderate rotation when the Rossby number is of order unity. At small Rossby numbers, the rotation differentiality is inhibited. A negative eddy viscosity is suggested for the case of rapid rotation. Some implications for the Sun and other astrophysical objects are discussed.

ISSN:0309-1929    

DOI:10.1080/03091928608245888

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We derive an equation governing the nonlinear propagation of a linearly polarized Alfvén wave in a two-dimensional, anisotropic, slightly compressible, highly magnetized, viscous plasma, where nonlinearities arise from the interaction of the Alfvén wave with fast and slow magnetoacoustic waves. The phase mixing of such a wave has been suggested as a mechanism for heating the outer solar atmosphere (Heyvaerts and Priest, 1983).

ISSN:0309-1929    

DOI:10.1080/03091928608245889

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

In this paper we consider the propagation of magneto-acoustic-gravity waves in a compressible, conducting isothermal atmosphere permeated by a uniform horizontal magnetic field. The singular levels, arising in a horizontal magnetic field, are considered in their most general form. Exact analytical solutions for a number of particular cases of wave propagation are obtained. The wave transformation is analyzed for all these cases using the solutions obtained.

ISSN:0309-1929    

DOI:10.1080/03091928608245890

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Recently Andrews has discussed an example of a topographically-forced non-zonal now satisfying the Arnold-Blumen sufficient condition for stability. At large distances from the topographic centre this flow becomes purely zonal and westward. After underlining the richness of solutions of the Andrews model, the present paper goes on to show that Andrews' technique can be applied successfully to a model where the vertical profile of static stability resembles those found in the ocean. In particular we obtain a large class of hydrodynamic stable flows, forced by the bottom topography, for continuously stratified fluids (two layers each with uniform Brunt-Väisälä frequency).

ISSN:0309-1929    

DOI:10.1080/03091928608245891

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The nonlinear stability properties of stationary exact nonzonal solutions for inviscid ilow over topography are examined within a barotropic model in spherical geometry. For stationary solutions, such that the potential vorticity is proportional to the streamfunction,necessary and sufficientconditions for nonlinear stability are established. For a truncated system with rhomboidal truncation wave numberJthese are that the solid body rotation component of the zonal winduibe negative, corresponding to westward flow, asJ→ ∞. These results are established by using the methods of statistical mechanics. The sufficient condition for stability is also established by applying Arnol'd's method.

ISSN:0309-1929    

DOI:10.1080/03091928608245892

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The linear, normal mode instability of barotropic circular vortices with zero circulation is examined in thef-plane quasigeostrophic equations. Equivalents of Rayleigh's and Fjortoft's criteria and the semicircle theorem for parallel shear flow are given, and the energy equation shows the instability to be barotropic. A new result is that the fastest growing perturbation is often an internal instability, having a finite vertical scale, but may also be an external instability, having no vertical structure. For parallel shear flow the fastest growing perturbation is always an external instability; this is Squire's theorem. Whether the fastest growing perturbation is internal or external depends upon the profile: for mean flow streamfunction profiles which monotonically decrease with radius, the instability is internal for less steep profiles with a broad velocity extremum and external for steep profiles with a narrow velocity extremum. Finite amplitude, numerical model calculations show that this linear instability analysis is not valid very far into the finite amplitude range, and that a barotropic vortex, whose fastest growing perturbation is internal, is vertically fragmented by the instability.

ISSN:0309-1929    

DOI:10.1080/03091928608245893

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An investigation is made of the evolution of small-scale, axisymmetric vortices in a stratified fluid with spatially variable Coriolis parameter. The criteria for smadness are a horizontal scale less than or equal to the first internal radius of deformation and a vertical scale less than or equal to that of the ambient stratification. These circumstances match those of Sub-mesoscale, Coherent Vortices frequently observed in the oceans. The dynamical model is the balance equations, which include various effects of finite Rossby number. The principal topics are the regime of nearly uniform propagation, the development of an equilibrium ratio of vertical and horizontal scales (i.e., Burger number selection), and the occurrence of various types of instability for vortices with extremes in amplitude or shape.

ISSN:0309-1929    

DOI:10.1080/03091928608245894

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor