Comment on the group velocity of surface waves on the plasma sheet boundary

Abstract

In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the Earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity of the compressional surface magnetohydrodynamic waves itself is nonzero transverse to the magnetic field—a characteristic which has been omitted in the spectrum of Chen and Hasegawa (1974), being used by Maltsev and Lyatsky. This characteristic of compressional surface MHD waves is inherent for the spectrum ω = ( k ‖ k )V A(k 2 ‖ + 2k 2 ⊥) 1 2 , obtained by Nenovski (1978) in the cold plasma limit V A ⪢ V S ( V A is Alfvén velocity, and V S , sound velocity). A comment has been made on the restrictions, proceeding from the approximation, used by Maltsev and Lyatsky. The estimation of the velocities for movements of auroral riometer absorption bays have been reviewed.