Tomikazu Namikawa

Exact solutions of magnetohydrodynamic equations for fluids in a circular magnetic field

Exact solutions of the nonlinear magnetohydrodynamic equations for a highly conducting fluid within an axisymmetric container are obtained. Attention is focused on fluids in which the unperturbed velocity and magnetic field are axially symmetric and purely zonal. It is shown that there are exact solutions with large amplitude but restricted form, indicating that an arbitrary disturbing force produces other motions as well as Alfven waves propagating along an azimuthal magnetic field whose strength varies with radius.

An exact nonlinear Alfvén wave solution in a toroidal magnetic field

Abstract The propagation of Alfven waves along a non-uniform toroidal magnetic field in a highly conducting incompressible fluid rotating uniformly is studied. It is shown that there is an exact Alfven wave solution with large but restricted form.

Surface-tension-driven convection under the simultaneous action of a magnetic field and rotation

Abstract Linear stability theory is applied to the problem of surface-tension driven convection when a magnetic field and rotation are simultaneously present. It is shown that the overall behaviour of a fluid is similar to that for the case of buoyancy-driven convection.

Propagation characteristics of hydromagnetic waves in a cold plasma mixed with a hot plasma and right-hand polarized Pc1 and Pc5

Abstract Propagation characteristics of hydromagnetic waves in a cold plasma mixed with a hot plasma under a uniform static magnetic field are investigated. The existence of cold plasma seriously affects the polarization properties of the waves. The results are applied to the interpretation of Pcl and Pc5 with righthand polarizations guided along the geomagnetic field line.

The α-effect generated by standing Alfvén waves

The mean electromotive force generated by nonlinear standing Alfven waves propagating along the mean magnetic field is investigated. It is shown that the alpha-effect can exist owing to the interaction between oppositely propagating two waves, provided that the initial fields have nonzero helicity. The result is discussed in the context of field-aligned currents and periodic particle flux variations in the earths magnetosphere.

Thermoconvective Waves in a Viscoelastic Liquid Layer

The propagation of thermoconvective waves in a horizontal layer of viscoelastic liquid (Oldroyds liquid B) heated from below is investigated. It is shown that the wave propagates without damping at the critical condition for the onset of overstability and that as the elastic parameter increases the damping length (the logarithmic decrement) becomes large (small) near the critical Rayleigh number for the onset of stationary instability. When the ratio of retardation time to relaxation time is very small, the weakly damped wave can exist for high frequencies even if the liquid layer is isothermal.

The effect of random Alfven waves on the propagation of hydromagnetic waves in a finite-beta plasma

Using first-order smoothing theory, Fourier analysis and perturbation methods, the evolution equation of the wave spectrum as well as the nonlinear forces generated by random Alfven waves in a finite-beta plasma with phenomenological Landau-damping effects are obtained. The effect of microscale random Alfven waves on the propagation of large-scale hydromagnetic waves is also investigated by solving the mean-field equations. It is shown that parallel-propagating random Alfven waves are modulationally stable and that obliquely propagating random Alfven waves can be modulationally unstable when the energy of random waves is converted to slow magnetoacoustic waves that can be Landau-damped, providing a dissipation mechanism for the Alfven waves.

Propagation properties of hydromagnetic waves in a hot plasma and right-hand polarized PC1 and PC5

Abstract Propagation characteristics of hydromagnetic waves in a hot plasma are investigated and the results are used to the interpretation of Pc1 and Pc5 with right-hand polarization guided along the geomagnetic field line.

The mean electromotive force generated by random hydromagnetic waves in a collisionless plasma

The mean electromotive force generated by random hydromagnetic waves is calculated by using Fourier analysis methods for the cases of an incompressible Hall plasma and a compressible plasma with finite β . It is shown that in the case of a Hall plasma the α effect can exist in the interaction between two waves which propagate in opposite directions and have different phase velocities and several new β –terms are produced by the Hall effect, while in the case of a compressible plasma the α –effect can exist only in the interaction between the Alfven mode and the fast or slow magneto-acoustic mode, and not between the fast and slow magneto-acoustic modes. The results are discussed in the context of the substorms in the earths magnetosphere.

Influence of proton heat fluxes on the propagation of hydromagnetic waves

Abstract It is shown that the propagation properties of hydromagnetic waves are asymmetric with respect to the direction of the magnetic field and the garden-hose instability criterion is modified by the heat flux anisotropy in the CGL approximation.