Magnetospheric substorms in the distant magnetotail observed by Imp 3

Variations of the magnetic field and plasma sheet in the distant magneto tail (20 to 40 RE) during magnetospheric substorms are studied on the basis of the Imp 3 magnetic-field and particle data. Depending on the locations of the satellite with respect to the boundary of the plasma sheet, the variations differ greatly. However, the present results and the results of other workers give a clear indication of an increase of the magnitude of the field outside the plasma sheet and of the simultaneous ‘thinning’ of the plasma sheet during an early phase of substorms. At about the maximum epoch or during the recovery phase of substorms, the plasma sheet expands and appears to be inflated to at least the pre-substorm level. Furthermore, a large excessive flux of the magnetic (∼Z component) field, as compared with the flux of the original dipole field, appears across the neutral sheet.