Characteristics of the three-dimensional hydromagnetic waves caused by the local source in a uniform cold plasma are studied. There are two modes of hydromagnetic waves. The one is an isotropic mode which spreads in all directions from the source and transmits the disturbance of magnetic field component parallel to field lines. The other is a mixed transverse mode consisting of two parts, the pure and the converted transverse modes, and communicates the signals of normal components of fields. It is emphasized that the former part is a one-dimensional wave propagating parallel to lines of force through the source region, while the latter is the converted one-dimensional wave from the three-dimensional isotropic mode with the geometrical attenuation. The space-time relations of disturbances belonging to the converted mode are obtained. The structures of hydromagnetic waves generated by the particular external forces, the partial compression and the azimuthal drag, are also presented. In a case of reflection of the transverse wave on the anisotropic conducting sheet, the quantitative relation between the incident electric field and the induced currents in the sheet is shown. Furthermore, space and time variations of hydromagnetic oscillations excited by the azimuthal stress and confined within the region between two parallel infinitely conducting solid are illustrated. With relation to the characters of three-dimensional hydromagnetic waves, qualitative discussion on some geomagnetic disturbances are given.
Society of Geomagnetism and Earth, Planetary and Space Sciences