摘要:

A new nonlinear mode of a density front is presented and we show that long, finite deviations from a steady state of the free streamlines of the coupled front of zero potential vorticity lead to oscillations of these streamlines about their initial locations. The amplitude and frequency of such oscillations are computed and it is found that the frequency depends on the initial displacement and is always higher than the inertial frequency. The results found for the free streamline behavior are also applicable to the coastal front in which the potential vorticity is zero and the along-stream velocity vanishes at the coast.

ISSN:0309-1929    

DOI:10.1080/03091928808213606

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A nonlinear barotropic model is used to examine the interaction of isolated vortices (i.e. patches of anomalous vorticity bounded by a free streamline) with vertical walls. The round undisturbed vortices are inviscid and contain cyclonic or anticyclonic circulation; they are embedded in a resting, infinitely broad ocean. The interaction is examined by, conceptually, “cutting” the vortices with a vertical wall at, say, t = 0. The resulting events are studied using a perturbation scheme in ε, the nondimensional distance between the wall and the undisturbed edge of the vortices. Analytical solutions for times ofO(f−1) (wherefis the Coriolis parameter) are constructed by applying the integrated momentum and continuity equations.

ISSN:0309-1929    

DOI:10.1080/03091928808213607

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Who show through numerical experiments that friction may enhance westward motion of vortices on the beta-plane and establish a relation betwen the dissipation coefficients and westward aceleration. This suggests an explanation fot the dunamics of westward intensification.

ISSN:0309-1929    

DOI:10.1080/03091928808213608

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The influences of nonlinear bottom friction on the along-isobath mean current associated with the topographic rectification of tidal currents are examined in the limit of depth-independence (no vertical structure in the horizontal currents), weak friction and weak nonlinearity. These influences are discussed in terms of the effects of spatial gradients and temporal variations in the effective friction coefficient relating bottom stress to velocity. For typical parameter values, spatial gradients in the coefficient enhance the mean current and temporal variations reduce it. The first influence is the source of Loder's (1980) suggestion that the mean current is enhanced by nonlinear friction. The second influence accounts for the mean current reduction upon the inclusion of nonlinear friction in the example considered by Huthnance (1981). However, it is shown that each of these influences can have the opposite effect for extreme parameter values. Additionally, the inclusion of mean current contributions to the friction coefficient can significantly increase the effective mean friction coefficient and hence also reduce the mean current. The results confirm that theformof bottom friction is important in models for the topographic rectification of tidal currents.

ISSN:0309-1929    

DOI:10.1080/03091928808213609

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This paper investigates the generation of linear baroclinic Rossby waves by a steady zonal current, which either translates at a constant speed or oscillates sinusoidally in latitudinal position. An analytical solution is found for forcing by a steadily moving current, and this confirms the numerical results. A numerical model, in a reduced gravity ocean, produces solutions for oscillating current forcing. All the results indicate a strong relationship between the wave crest orientation (and phase speed direction) of the response, and the speed of motion of the current. This is elucidated by reference to the work of Lighthill (1967) on moving forcing effects.

ISSN:0309-1929    

DOI:10.1080/03091928808213610

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

In 1969 A. E. Gill showed that convection in a porous vertical slab is not possible when the temperature difference is maintained across the layer. He attributed this to the lack of fluid inertia in Darcy's law and based his arguments on two-dimensional linear stability theory. We readdress the Gill problem but by using integral inequality estimates on the full three-dimensional nonlinear theory. We again find there is always stability, but now provided the initial data are less than a threshold which is proportional to the inverse of the Rayleigh number. Of course, this is in complete agreement with the result of Gill, although we believe it adds insight into the physical situation.

ISSN:0309-1929    

DOI:10.1080/03091928808213611

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We consider standing wave solutions of the linearized magnetohydrodynamic (MHD) equations describing a perfectly conducting but viscous magnetofluid in a gravitationally-stratified cylindrical plasma. We assume a relatively strong homogeneous background magnetic field within the flux tube, which is oriented along the cylinder axis; the background atmosphere is in hydrostatic equilibrium, with gravity uniform and parallel to the cylinder axis; the vertical temperature profile (constrained by the stability conditions) is arbitrary. The MHD wave equations are separable, and appropriate boundary conditions are formulated. We employ a numerical shooting scheme to solve the coupled ordinary differential equations and to obtain the damping rates and eigenfrequency spectra for the standing MHD wave modes. Three series of modes are obtained for an isothermal flux tube: Alfvtnic, quasi-fast, and quasi-slow. The quasi-slow mode series is novel, having been missed previously. In the inviscid limit, with a strongly stratified atmosphere, we use three approximate characteristic dispersion relations to reveal the physical nature of the three MHD eigenmode series. The relevance of the present investigation to umbral oscillations in sunspots is briefly discussed.

ISSN:0309-1929    

DOI:10.1080/03091928808213612

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

G. I. TAYLOR, Journal of Fluid Mechanics, Vol. 173, Cambridge University Press, 1986, x + 709 pp., $66.00.

ISSN:0309-1929    

DOI:10.1080/03091928808213613

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

by P. L. Sachdev, Cambridge University Press, 1987, vii+ 246 pp., US $49.50 (ISBN 0-521-265 93-2).

ISSN:0309-1929    

DOI:10.1080/03091928808213614

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

By Rolf Meissner, Academic Press/Harcourt Brace Jovanovich, Orlando, Florida, 1986, 426 pp. $70.00 cloth, $34.95 paper. (ISBN 0-12-488950-6).

ISSN:0309-1929    

DOI:10.1080/03091928808213615

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor