Magnetospheric substorms observed at the synchronous orbit

The behavior of the magnetic field at the synchronous orbit during magnetospheric substorms is discussed for several events during December 1966 and January 1967. The vector measurements of the field were made with magnetometers on board the geostationary satellite ATS 1. The field was observed to be depressed and inclined radially outward in the dusk-to-midnight quadrant while substorms were in progress. Similar distortions of the magnetosphere were not observed in other local-time sectors. When the satellite was near local midnight, the onset of the expansive phase of an auroral substorm was coincident with the recovery of the field at ATS 1. When the satellite was further toward the dusk meridian similar recoveries were observed, but they were followed by a renewed depression in the field. An interpretation of the data in terms of partial ring currents in the dusk-to-midnight quadrant is discussed.