LINEAR MAGNETOSONIC N-WAVES AND GREEN-FUNCTIONS

Fourier analysis is used to consider the characteristics of linear mag netosonic N waves propagating through a uniform background medium at r est, with constant uniform magnetic field B0. The disturbance is drive n by an initial compressed and localized gas pressure perturbation, re presented by a Dirac delta distribution. The solutions for the perturb ed gas and magnetic field variables are expressed as second derivative s of appropriate wave potentials. The wave potentials split naturally into fast and slow magnetosonic components. The fast- and slow-mode wa ve potentials reduce to one-dimensional integrals over the wave normal angle theta between the wave vector k and B0. Alternatively, the fast -mode wave potentials can be written as Abelian integrals over the slo w-mode phase speed c(s), whereas the slow-mode potentials reduce to Ab elian integrals over the fast-mode phase speed c(f). The structure of the integrals depends on the location of the observation point relativ e to the fast and slow magnetosonic eikonal or group velocity surfaces . Calculations of the time evolution of the magnetic field of the N wa ve show a family of magnetic field fines connecting the cusps of the s low magnetosonic group velocity surface, plus a further family of fiel d lines not connected with the cusps. The wave disturbance is confined on and within the fast magnetosonic group velocity surface. The gas p ressure perturbation shows singular N wave type disturbances on the fa st- and slow-mode eikonal surfaces. The Green's function for the magne to-acoustic wave operator for a uniform background medium initially at rest is also obtained. Generalization of the N wave solutions for non -singular distributions of the initial gas pressure perturbation are a lso obtained.