摘要:

The effect of mixing on a zonally stationary modon (Stern's modon) and rider is analysed using the method of multiple scales. Cases in which only the rider contributes to the mixing, or only the modon mixes, or a combination of both, are considered separately. In each case the mixing is shown to establish a dipole field aligned in such a manner to drive meridional motion in a direction dependent on the type of mixing. Moreover, the radius and amplitude of the modon and rider field are shown to decrease in response to mixing. The rule by which they decrease is dependent on the type of mixing. For the particular case when both the modon and rider fields contribute equally to the mixing, it is shown that cyclones propagate north and anticyclones propagate south.

ISSN:0309-1929    

DOI:10.1080/03091929508229067

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A uniform asymptotic analysis of unsteady storm surges due to surface winds of the formS(r)exp(—iωt)H(t),,H(t) = Heaviside unit function], near a circular islandr=ais carried out for large times and distances. Assuming that the undisturbed depth ish1(r/a)α forr>a, with α ≥ 0 andh1= constant, some interesting features of the motion are described. These include, amongst others, several characteristics along with a graphical illustration of the asymptotic envelope of the dominant progressive long wave generated.

ISSN:0309-1929    

DOI:10.1080/03091929508229068

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A model of a homogeneous isotropic turbulent flow is presented. The model provides different realizations of the random velocity field component with given correlation latitudinal and lateral functions and a spatial structure which obeys the Kolmogorov theory of homogeneous and isotropic turbulence. For the generation of the turbulent flow the structural function of the flow in the form suggested by Batchelor (Monin and Yaglom, 1975) was used. This function describes the spectrum of turbulence both in the viscous and inertial ranges. The isotropy and homogeneity of the velocity field of the model are demonstrated.

ISSN:0309-1929    

DOI:10.1080/03091929508229069

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this paper, we investigate the problem of the effect of Newtonian cooling on vertically propagating magneto-acoustic waves resulting from a uniform horizontal magnetic field in a viscous and thermally conducting isothermal atmosphere. We consider the case in which the combined effect of the viscosity and the magnetic field is large compared to that of the thermal conduction. It will be shown that the atmosphere may be divided into two distinct regions connected by a transition layer in which the reflection and the modification of the waves take place. In the lower region the effect of the thermal diffusivity, kinematic viscosity and Alfvén speed is negligible, whereas in the upper region the effect of these quantities is more pronounced. Moreover, if the Newtonian cooling coefficient is large compared to the adiabatic cut off frequency, it will act directly to eliminate the temperature perturbation associated with the wave in a short time compared to the period of oscillation. This eliminates the attenuation in the amplitude of the wave since the isothermal regime is dissipationless. Also, the magnitude of the reflection coefficient depends on the relative strength of the viscosity with respect to the magnetic field. The reflection coefficient and the attenuation factor are derived for arbitrary values of the Newtonian cooling coefficient. This problem leads to a singular perturbation problem which may be solved by matching inner and outer approximations in an overlapping domain.

ISSN:0309-1929    

DOI:10.1080/03091929508229070

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this paper, the turbulent diffusion of a magnetic field in the kinematic approximation, i.e., kinematic dynamo theory, is studied in the context of spectral densities rather than mean fields. In particular, we derive the evolution equations for the magnetic energy and helicity spectra, given the corresponding kinetic energy and helicity spectra. We verify that for the kinematic turbulent diffusion problem, the total magnetic helicity remains an exact invariant—as it must for ideal magnetohydrodynamics; and that with the use of inequalities connecting the magnetic energy and helicity spectra, one can place bounds on the magnetic energy spectrum which depend on the field topology.

ISSN:0309-1929    

DOI:10.1080/03091929508229071

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Mean-field electrodynamics, including both the α-effect and the effect of Lorentz forces damping action on small-scale helical fluid motions (the latter taken in the limit of low magnetic Reynolds number values) is formulated for the electrically conducting, rotating, inviscid Boussinesq fluid. A self-consistent system of two coupled ordinary differential equations in terms of mean magnetic field intensity and helicity bulk density is derived for the case of spatial homogeneity and isotropy. The mean-field induction equation takes into account both the α-effect and the effect of magnetic viscosity. The helicity balance equation contains the helicity source due to buoyant forcing and the helicity sink because of Ohmic dissipation. This system has the unique stationary solution, which is the global attractor, and describes the saturated values of mean magnetic field intensity and helicity. Possible implications to the problem of the terrestrial magnetism are discussed briefly.

ISSN:0309-1929    

DOI:10.1080/03091929508229072

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Maximally-Efficient Generation Approach (MEGA) for an αω-dynamo is investigated based on the simplest model of the Parker Migratory Dynamo. The α-effect is supposed inhomogeneous. The equations which govern the magnetic field are solved with the use of a WKB method. Turning points and the behavior of the solution in their vicinity are derived. The point of maximum dynamo wave amplitude is shown to be shifted from the point where the generation sources are maximum towards the direction of the dynamo wave propagation. For the solar dynamo the obtained direction of the dynamo wave propagation reverses over the subpolar domains. Dynamo waves with a poleward migration are observable over the polar regions of the Sun. The generation threshold is calculated. The properties of the dynamo waves are compared with observational data for the solar cycle. An asymptotic solution for oscillating modes of the galactic disk dynamo is also obtained.

ISSN:0309-1929    

DOI:10.1080/03091929508229073

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor