Transient Proccsses near the Dayside Magnetopause Associated with Solar Wind Changes

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Based on Geotail observations near the dayside magnetopause on October 17-18 and November 4,1992, we have studied oscillatory variations at the magnetopause and in the magnetosphere. The results are summarized as follows :1. Magnetopause crossings, associated with the northward interplanetary magnetic field (IMF) observed on November 4, were characterized by quasi-periodic pulses of a sawtooth wave form in the magnetic filed and the plasma flow components tangential to the magnetopause. The direction of magnetic field outside the magnetopause current layr was northward with antisunward tilt, indicating the draping of magnetic filed on the magnetopause. Boundary normals of wavy magnetopause systematically inclined sunward on the upstreamside, while they tend to incline antisunward with considerable deviation on the downstream side. 2. When the magnetopause crossings were observed in association with the southward IMF,we also observed a clear inbound/outbound dependence of the magnetopause orientation consistent with the tailward-moving recurrent bumps at the magnetopause. However, recurrence of tailward-moving structures is less regular than that for the case of northward IMF.In addition, there is an implication that the northward (southward) flow along the magnetopause occurred for the inward (outward) directed magnetic filed component nonnal to the magnetopause. 3. Pc5 and compressional Pc3 pulsations were observed in the dayside magnetosphere on October 17-18. The signature of the Pc5 pulsations agrees with the theory of file line standing oscillations with the mode being the fundamental. The observed Pc5 pulsations were regarded to be triggered by sudden compressions and expansions of the magnetosphere. On the other hand, compressional Pc3 pulsations are consistent with fast magnetosonic waves propagating earthward.