Magnetospheric energy principle for spherically symmetric monopolar magnetospheres.
A new magnetospheric energy principle is developed for spherically symmetric monopolar magnetospheres with open straight field lines. The principle is based on the self-adjointness of the force operator, which ensures energy conservation in the unperturbed magnetospheric plasma volume. A Neuman-type boundary condition for the perpendicular displacement at the ionosphere yields a negative contribution to the potential energy variation. This contribution makes high-mode-number incompressible field-line-bending modes unstable owing to the plasma displacement over the spherical ionospheric surface.