摘要:

The effect of the horizontal structure of midlatitude oceanic heating on the stationary atmospheric response is examined by means of a simple continuously stratified quasigeostrophic model, linearized about a basic state with constant zonal flowUo, on a beta plane. Solutions are obtained for three non-periodic zonal heating structures (line source, rectangular, and segmented cosine), and these are compared with the solution for the frequently used zonally periodic heating distribution. All four heating distributions assume an e−αzvertical structure and a cos ly meridional structure.

ISSN:0309-1929    

DOI:10.1080/03091928808208830

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This is a broad survey of the interaction of modons with topography in a one-layer, quasigeostrophic model. Numerical simulations of modons interacting with ridges, hills, random topography and other obstacles are presented. The behavior of the modon is compared to numerical simulations of a two-point-vortex model, which proves a useful guide to the basic trajectory deflection mechanism. Under sufficiently strong but quasigeostrophically valid topographic perturbations, the modon is shown to fission into two essentially independent, oppositely-signed vortices. In the breakup of a modon near a hill it is found that the positive vortex migrates to the top of the hill. The resulting correlation between the positive vorticity trapped over the hill and the topography is in sharp contrast with the theories of turbulent flow over topography and generation of flow over topography by large scale forcing, both of which describe the development of vorticity anticorrelated with topography. A heuristic explanation of this new behavior is provided in terms of the dynamics of β bT-plane vortices. Further, it is found that a modon travelling over rough topography homogenizes the field of potential vorticity in its vicinity. This behavior is explained in terms of the induced eddy activity near the modon.

ISSN:0309-1929    

DOI:10.1080/03091928808208831

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

An attempt is made to understand the channelling effect observed in the Rhine valley by the use of simple models. We consider two-dimensional flow of a homogeneous rotating viscous fluid over a valley. Two different approaches are described: (i) a linear theory of a horizontally averaged flow over a valley of finite depth; (ii) a numerical model. The linear theory gives wind profiles in the valley which compare favorably with the results of the nonlinear numerical model. There is qualitative agreement with observations. An analysis of the linear solution reveals that the channelling effect is a feature of Ekman flow where advection is important above the valley, but not in the valley.

ISSN:0309-1929    

DOI:10.1080/03091928808208832

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A simple model is considered describing tidal effects in a plane alluvial river with a mean seaward flow. The effects of quadratic resistance and sediment transport are accounted for in the model. It is shown that quadratic resistance introduces exponential decay of tidal effects together with a phase change between the free surface and the fluid velocity. The dissipation length and the phase change are examined quantitatively.

ISSN:0309-1929    

DOI:10.1080/03091928808208833

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The two dimensional incompressible MHD equations describing the decay of a random initial velocity field in the presence of a uniform magnetic background field are solved numerically by a Chebyshev spectral method. The nonlinear interactions of standing Alfvén-waves of a given energy are studied for various Reynolds numbers and field strengths of the magnetic background field. Small scale structures are generated by these interactions, which increase the energy dissipation, however, the uniform background field suppresses the production of arbitrary small scales. Thus energy dissipation is found to be insignificant at sufficiently high Reynolds numbers. Anisotropies of the fluctuating field components are also studied. In the temporal evolution they appear first in the magnetic field. This is explained by the conservation of mean square vector potential in the limit of infinite conductivity.

ISSN:0309-1929    

DOI:10.1080/03091928808208834

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor