REFLECTION OF SHEAR ALFVEN WAVES AT THE IONOSPHERE AND THE DIVERGENT HALL CURRENT

A general expression for the reflection and mode conversion of MHD wav es at the ionosphere is derived. On the basis of the expression, the e ffect of ionospheric divergent Hall current (Hall part of the inductio n current associated with the inductive electric field of fast magneto sonic wave) on localized toroidal oscillation is examined. When the ho rizontal scale of localized oscillation is of the order of several tim es of the height of ionosphere, the inductive electric field can play a significant role in the reflection of shear Alfven waves with longer periods (e.g., similar to 100 s) in the high-latitude region, especia lly, in the auroral zone. Then, the contribution of the divergent Hall current to the field-aligned one can be no longer neglected and so th e eigenfrequency of localized toroidal oscillation is effectively cont rolled by the height-integrated Hall conductivity in the ionosphere.