Hydromagnetic wave coupling in the magnetosphere—magnetic fields and poynting fluxes

Abstract Using a numerical model with cylindrical geometry, we further extend the picture of impulsively-stimulated hydromagnetic wave coupling in our model magnetosphere by examining the structure of the magnetic fields associated with previously-derived hydromagnetic wave electric fields, for two radial Alfven speeds models, one including a plasmapause at L = 4. We also evaluate the time-integrated Poynting vector to estimate net energy flow in these models. The transverse magnetic field components behave much as expected, except for a geometrical enhancement which becomes obvious for small radial distance. The compressional magnetic field components are found to have “near nodes” at certain radial positions where nodes would be expected. At these “near nodes” the amplitudes do not reach zero and phase changes of less than π occur over extended radial distances. This behaviour is interpreted in terms of “reflection” and “coupling” points of the governing hydromagnetic equations. Asymptotic values of the time-integrated Poynting vector in the case without a plasmapause show that energy flow into the ionosphere via field-line resonances is dominated by the outermost (lowest frequency) resonance. However, significant energy flow into the ionosphere is generated by transient field-line oscillations and by the initial compressional impulse. With the plasmapause at L = 4, field-line resonance energy flow into the ionosphere is completely dominated by a double resonance at the plasmapause. Energy flow into the ionosphere from transient fields is still significant.