Low-frequency waves and electric fields in the magnetospheric current sheets

Low-frequency distrubances in a plasma immersed in a force-free magnetic field Bo characterized by a zero-order field-aligned current J are analyzed in the shortwave approximation. Parallel electric field E parallel (always small in comparison with E perpendicular) often substantially modifies the properties of waves in the typical current sheets in the enar-Earth magnetosphere. The mode of oscillations corresponding in the limit J = 0 to the Alfven mode is partly or totally absorbed on the auroral oval field lines. Conditions under which optimum absorption occurs are pointed out. The second mode of oscillations, which correspond to the compressional wave in the limit J = 0, is not substantially affected by the magnetospheric current sheets