摘要:

A series of laboratory experiments have been carried out which demonstrate the conditions favourable for vacillation in baroclinic thermally driven flows in a rotating annular convection chamber. As earlier studies have indicated amplitude vacillation occurs close to the transitions between dominant wave numbers in the regime under which regular waves are observed. Amplitude vacillation is shown to be less common when the depth of the system is decreased; it is not greatly affected by the use of a free or rigid upper boundary condition. It is however much more frequent when the Prandtl number of the convecting fluid is increased from 11 to 74 although in these experiments other parameters of the system, eg the isotherm slopes, were necessarily changed. Shape vacillation is only significant in the experiments when the upper surface is free; it is not influenced by the nature of the fluid.

ISSN:0309-1929    

DOI:10.1080/03091928108208771

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The mutual interaction of fields induced by spatially separated potential vorticity sources in a quasi-geostrophic barotropic flow is investigated using the weakly nonlinear approach. It is found that a powerful nonlinear response can be triggered by Rossby lee waves. This resonance phenomenon which dominates all other nonlinear corrections depends on certain global resonance conditions and on the change in the phase of the Rossby lee wave across the distance separating the sources. The response is particularly strong for topographic forcing possessing δ-function characterisitics.

ISSN:0309-1929    

DOI:10.1080/03091928108208772

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

We calculate the trajectories of particles in two-dimensional model flows typifying atmospheric or oceanic eddy motions. Rather than restricting the flows to be weak (but solutions to the relevant dynamics), we have considered motions where the streamfunction is only a kinematic model resembling the actual flows but the amplitude can be large so that flow speeds can greatly exceed the phase speed. For steadily propagating disturbances, there is an equivalent one-dimensional Lagrangian motion problem and we have applied results from analyses of such to periodic channel waves and isolated circular eddies. We show that the mean Lagrangian drift rate in periodic channel waves is very sensitive to the initial position and may be either prograde or retrograde. Large volumes of the fluid may be “trapped” to translate along with the wave. The wave drift depends on the phase velocity relative to the Eulerian mean flow and peaks at about 1/3 of the transient Eulerian speed at geophysically relevant amplitudes. For isolated eddies such as Gulf Stream rings, we calculate the trapped volume carried with the eddy and the displacements of the particles outside. We show that some particles may translate quite large distances along with the eddy while others move rapidly in the opposite direction and are left behind.

ISSN:0309-1929    

DOI:10.1080/03091928108208773

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

In Naeser (1979), later denotedN, it was shown that a frequency shift of a wave spectrum had to be expected as a result of dissipation of energy and conservation of spin of the waves. While time-dependency was treated inN, mainly space-dependency is treated here. In order to do this, the velocity of the spin of the waves is calculated. It is shown that this can be made equal to the group velocity by a second order coordinate transformation. In the limits of deep and shallow water the transformation becomes the identity, and leaves the Stokes drift at its usual value if the moment point is located at the mean water level.

ISSN:0309-1929    

DOI:10.1080/03091928108208774

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Results are presented of calculations on the generation of residual vorticity by tidal currents over the bottom topography of the Southern Bight of the North Sea. A typical order of magnitude is 10−6to 10−7s−1. This is compared with current measurements on calm days, when similar magnitudes are found. At windspeeds less than about 5 m/s tidal generation of residual vorticity is important; at higher windspeeds wind effects begin to dominate. Our results are relevant in understanding the spatial variability of residual currents, because a non-zero vorticity implies the existence of horizontal gradients in the residual current field.

ISSN:0309-1929    

DOI:10.1080/03091928108208775

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Experimental investigations of the surface discharge of two-dimensional heated saline jets into surroundings with stable, constant salt gradients were carried out. The discharge conditions were parameterized with the densimetric Froude number, and the Reynolds number. The evolution of the discharge was monitored by flow visualization methods, and by the measurements of temperature and salinity distributions. For comparison, experiments of the surface discharge of heated water into homogeneous surroundings at the corresponding discharge conditions were also conducted. The results clearly showed that while in the former case, the region away from the vicinity of the discharge manifold was marked by the presence of salt-finger convection, in the latter case this region exhibited stable thermal stratification. Furthermore the occurrence of salt-finger convection considerably retarded the motion of the jet, and increased the penetration depth of temperature and salinity fields.

ISSN:0309-1929    

DOI:10.1080/03091928108208776

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The problem of the removal of the degeneracy of the patterns of convective motion in a spherically symmetric fluid shell by the effects of rotation is considered. It is shown that the axisymmetric solution is preferred in sufficiently thick shells where the minimum Rayleigh number corresponds to degreel= 1 of the spherical harmonics. In all cases withl> 1 the solution described by sectional spherical harmonicsYll(,) is preferred.

ISSN:0309-1929    

DOI:10.1080/03091928108208777

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Two alternative methods are described for obtaining inviscid velocity components at the surface of earth's liquid core, assumed perfectly conducting, given perfect and complete measurements of the geomagnetic main field and secular variation at earth's surface. The mantle is treated as a spherically-symmetric insulator for purposes of extrapolation to the core. Both methods utilize the vertical component of the induction equation and require one-dimensional interpolation along special curves on the core surface as the initial step. For the next step, the first method then utilizes the two horizontal components of the induction equation, whereas the second method relies on the horizontal components of Ohm's law. Both methods work within the confines of the ambiguity elucidated by Backus (1968) but nonetheless can still yield results of value, because the two horizontal velocity components are determined separately and at distinct locations. A brief comparison of the two methods suggests that the one, based in part on Ohm's law, should be superior from a practical viewpoint.

ISSN:0309-1929    

DOI:10.1080/03091928108208778

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor