摘要:

A large-scale circulation in the form of azimuthal (east-west oriented) rolls has been discovered in the convection zone of the Sun (Ribeset al.0, 1985; Ribes, 1986). The characteristics of the global circulation (for example orientation, number, lifetime and so forth) are quite different from those of meridional cells (oriented parallel to the solar axis) which has been predicted by theory (e.g. Glatzmaier, 1985). This raises the important question as to whether or not the newly-discovered azimuthal rolls contribute to the transport of heat from the deep interior of the Sun to its surface. Here we report new results that exhibit the convective nature of the azimuthal rolls. These are based on 22 years of observation of the roll pattern (Ribes, 1986), a 11 year sequence of solar diameter measurements (Laclare, 1987), and four years of luminosity measurements (Willsonet al., 1981). The first indication is provided by the distribution of solar activity, which frames the roll pattern rather than being superimposed on it. The second hint comes from a temporal association that exists between the onset of new rolls and the luminosity and diameter oscillations with a period of 980 days.

ISSN:0309-1929    

DOI:10.1080/03091928808208849

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We consider the formation of small-scale magnetic structures in solar coronal loops, with the aim of understanding the possible role of these structures in the process of coronal heating. A simplified model of a coronal loop is discussed. Neglecting loop curvature, we consider an initially uniform magnetic field embedded in a perfectly conducting plasma between two flat parallel platesz=0 andz=L, which represent the photosphere at the two ends of the loop. Slow, random motions at these boundary plates produce twists and braids in the magnetic field. We discuss the properties of such braided fields assuming the field evolves through a series of force-free equilibria.

ISSN:0309-1929    

DOI:10.1080/03091928808208850

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The stability of a horizontal layer of Boussinesq fluid, heated from below and cooled from above, rotating uniformly about the vertical in the presence of a uniform vertical magnetic field is studied for the case where the thermal diffusivity K is much larger than the magnetic diffusivity η(= 1/μσe'where μ is the magnetic permeability and σeis the electrical conductivity). The stability problem depends on the five dimensionless numbersRa, T, M, q, qb. The Rayleigh number,Ra, is a measure of the buoyancy force, the Taylor number,T, is a measure of the Coriolis force, the Hartmann number,M, is a measure of the Lorentz force andq=k/η, whileqb=Kμσb'where σbis the electrical conductivity of the boundary.

ISSN:0309-1929    

DOI:10.1080/03091928808208851

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

In slightly viscous rotating stratified systems weak potential vorticity sources can excite finite amplitude response when the group velocity of the long waves vanishes. This mechanism is used, in a two layer fluid, to generate steady state solutions that can be characterized as currents. The currents are strongly sheared in both the vertical and the meridional directions but they vary slowly in the zonal direction. Numerical simulations reveal that the currents are unstable with respect to small perturbations and that the unstable response is dominated by trapped eigenmodes. A WKB analysis jointly with a second order turning point problem are used to derive a consistent description of the spatial and temporal characteristics of the unstable eigenmodes. The stability analysis is applicable to zonally varying basic states whose zonal gradient vanishes at some isolated points of the flow domain.

ISSN:0309-1929    

DOI:10.1080/03091928808208852

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 an imposed current distribution, in a reduced gravity ocean, both with and without an eastern coast. A zonal current is impulsively applied and maintained along the northern edge of the domain of solution. Using Green's function techniques, analytical solutions are found, and these are evaluated for small times. Numerical solutions are obtained for larger times. The upper layer depth field consists of a transient response, due to the sudden application of the current. Maintenance of the current causes a response which is singular along the line of imposed non-zerohy. The interior field decays with time (this is shown asymptotically). The parameters used are appropriate for the mid-latitude North Pacific, and the results are relevant to sudden transport changes in the North Pacific Current.

ISSN:0309-1929    

DOI:10.1080/03091928808208853

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The model equations describing two-dimensional thermohaline convection of a Boussinesq fluid in a rotating horizontal layer are known to support multiple instabilities, depending on the values of certain control parameters (Arneodoet al., 1985). Most of these multiple instabilities have already been studied for double or triple diffusive convection, where behaviours ranging from simple steady to irregular motions have been found. Here we consider the one remaining bifurcation mentioned by Arneodoet al.(1985): the interaction between a steady and an oscillatory convection roll when the linear spectrum for a single wavenumber comprises one zero and one pair of purely imaginary eigenvalues. The method of centre manifolds and normal forms is used to derive evolution equations for the amplitudes of the convection rolls close to bifurcation and the behaviours associated with the equations is discussed.

ISSN:0309-1929    

DOI:10.1080/03091928808208854

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The connection between the effective convection velocities for scalar and vector fields due to the action of turbulence is discussed. An explicit relation between the two is calculated for the special case of two-dimensional flows and fields and it is shown that both velocities are zero for homogeneous turbulence. The calculation leads to new insights on the rde of symmetry in determining the advection velocity for the case of a vector field.

ISSN:0309-1929    

DOI:10.1080/03091928808208855

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor