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Abstract We study a semi-analytical model of convection in a rapidly-rotating, differentially-heated annulus with sloping top and bottom lids. Rapid rotation leads to a preservation of relatively simple, two-dimensional (2-D) structure in the experimentally-observed flow, while temporal complexity increases with the Rayleigh number. The model is, therefore, two-dimensional; it exhibits a sequence of bifurcations from steadily-drifting, azimuthally-periodic convection columns, also called thermal Rossby waves, through vacillation and a period-doubling cascade, to aperiodic, weakly-turbulent solutions. Our semi-analytical results match to within a few percent previous numerical results with a limited-resolution 2-D model, and extend these results, due to the greater flexibility of the model presented here. Two types of vacillation are obtained, which we call, by analogy with classical nomenclature of the baroclinic annulus with moderate rotation rates, amplitude vacillation and tilted-trough vacillation. Their properties and dependence on the problem's nondimensional parameters are investigated. The period-doubling cascade for each type of vacillation is studied in some detail. 相似文献
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Abstract 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 degree l = 1 of the spherical harmonics. In all cases with l > 1 the solution described by sectional spherical harmonics Yl l (θ,φ) is preferred. 相似文献
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The magnetohydrodynamic dynamo problem is solved for an electrically conducting spherical fluid shell with spherically symmetric distributions of gravity and heat sources. The dynamics of motions generated by thermal buoyancy are dominated by the effects of rotation of the fluid shell. Dynamos are found for low and intermediate values of the Taylor number, T ? 105, if the scale of the nonaxisymmetric component of the velocity field is sufficiently small. The generation of magnetic fields of quadrupolar symmetry is preferred at Rayleigh numbers close to the critical value Rc for onset of convection. As the Rayleigh number increases, the generation of dipolar magnetic fields becomes preferred. 相似文献
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Abstract This Special Issue was originally conceived as an opportunity to publish together papers presented at or submitted for the symposium “Models of the Geodynamo and Core-Mantle Coupling” as part of the International Association of Geomagnetism and Aeronomy (IAGA) 7th Scientific Assembly held in Buenos Aires during August 1993. This Symposium (1 .l) was convened by Michael Proctor and Ivan Cupal. While a large proportion of the papers fall into this category, in the interests of a more harmonious whole it has been decided to adjoin some others. These latter, while not directly connected with the meeting, nonetheless address problems in the same area of geomagnetism, and their presence will, it is hoped, enhance the impact of the Issue. 相似文献
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F. H. Busse 《地球物理与天体物理流体动力学》2013,107(1):325-326
Abstract by J. A. Jacobs, 1975, Academic Press, London, New York, San Francisco, U.S.A., viii + 253 pages. 相似文献
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F. H. Busse 《Pure and Applied Geophysics》1983,121(3):375-390
The major planets produce heat flux from their interiors that is comparable to the radiative flux they receive from the sun.
The dynamics of convection flows carrying the heat flux are discussed, and the dominating effect of the Coriolis force is
demonstrated. The characteristic high-velocity jets in the atmospheres of Jupiter and Saturn can be explained on the basis
of Reynolds stresses generated by the fluctuating convective motions. A simple annulus model, which elucidates the more complex
mathematical analysis of the spherical case given in an earlier paper (Busse, 1983), is considered in detail. Various aspects of the observational evidence are discussed in relation to the model. 相似文献
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F. H. Busse 《Surveys in Geophysics》2003,24(3):269-288
The sequence-of-bifurcations approach for the analysis of transitionsfrom simple to complex forms of fluid flow is described.Formulated for fluid systemswith external conditions that are homogeneous in two spatial dimensionsand in time,this approach determines bifurcations through theirsymmetry breaking properties.Solutions that are periodic in the homogeneous dimensionsand in time are generatedin this way. While the secondary solution induced by theinstability of the basichomogeneous state generically assumes the form of rolls orstripes, higher bifurcationsintroduce solutions exhibiting structures specific for thephysical system underconsideration. These structures often persist in the formof coherent structures inthe turbulent state of the system. Examples from the caseof thermal convection in alayer heated from below are used to illustrate thesequence-of-bifurcations approach. 相似文献
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Desalinization effects on benthic diatom communities were investigated in two adjacent streams in Northern Thuringia, the creek Urbach and the river Helbe. Salt-saturated stockpile effluents had been introduced into the Urbach until 1996, resulting in fluctuating chloride concentrations with maximum values up to 25.4 g · 1−1 (Helbe: max. 3.7 g · 1−1).
The diatom vegetation and hydrographical and chemical data of an Urbach site were compared to those of a sampling site further downstream. Monthly sampling in 1996 started at the end of salt influx in January. Reference samples from the years 1995, 1986 and 1963 were evaluated along with the 1996 samples.
After termination of the introduction of salt-loaded effluents, relative abundances of brackish water species greatly decreased within three months. The Halobion Index (Ziemann 1982), reflecting osmotic and ion composition effects on diatoms, decreased until May 1996, then stabilized. In summer 1996, several diatoms had a mass development, showing that salinization impacts had previously overruled effects of other environmental variables. 相似文献