On the stratification of the magnetospheric convection

Stability of the large-scale stationary convection in the Earth magnetosphere relative to low-frequency electromagnetic perturbations has been considered. Excitation of the small- scale (across a magnetic field) Alfven waves at the expense of relative motion of electrons and ions in ionosphere has been investigated in the magnetic field of the dipole configuration. Interaction of magnetosphere and ionosphere was taken account of by means of a boundary condition on the ionospheric base which is true in the case of very stretched perturbations along the magnetic field. A dispersion equation has been derived and investigated with provision for a real altitudinal profile of electron and ion velocities in the ionosphere. The instability described is used to explain periodical structures-arcs of aurora polaris existing in the ionosphere