Observation of reconnection phenomena at synchronous orbit

Abstract

On October 6, 1979, the solar wind pressure increased suddenly causing earthward motion of the magnetopause in past 6.6 RE. Plasma and magnetic field measurements were made in the magnetosheath and boundary layer close to the magnetopause in the noon sector. Large‐amplitude variations in the magnetosheath magnetic field intensity with a quasi‐period of 10 s were observed. Nearly static structures of high‐β plasma associated with the magnetic field minima and low‐β plasma associated with the magnetic field maxima were observed convecting toward the earth. Flux transfer events were observed at the magnetopause with the same time scale and amplitude as the magnetosheath magnetic field variations in the southward magnetosheath magnetic field. No flux transfer events were observed during an extended period of northward magnetosheath magnetic field. The morphology of charged particle data for the transition between the magnetosphere and the magnetosheath for a northward magnetosheath magnetic field is presented. A convection electric field of ∼9 mV/m was inferred from the spectral difference between solar and antisolar drifting ions in the magnetosheath near a magnetopause rotational discontinuity. A trapped component was observed in the magnetosheath plasma during both northward and southward magnetosheath magnetic fields. It is concluded that flux transfer events result from the interaction of the earthward convecting plasma filaments with magnetospheric magnetic field at the magnetopause. The estimated flux erosion from the dayside magnetosphere is ∼3×1011 Mx/s.