Satellite studies of magnetospheric substorms on August 15, 1968: 4. Ogo 5 magnetic field observations

In this paper we examine the changes in the magnetic field on the midilight meridian 15-8 R/sub E/ behind thc earth. These changes are conveniently divided into two main phases: a growth phase and an expansion phase. The beginnings of the growth phase coincide within experimental error to the arrival of a southward solar wind magnetic field at the dayside magnetopause and also to the beginning of the growth phase at synchronous orbit and ground observatories. During the growth phase the magnitude of the field increases in the lobe of the tail. In the cusp both the magnitude and the inclination of the field incrcase. Slow changes in the cross-tail field aecompany these effects. Nearly coincident with the onset of the polar substorm the lobe field magnitude begins to decrease, the cusp field magnitude and inclination decrease, and there are sudden changes in the cross-tail field. About this time the plasma sheet begins to expand. Inside the expanding plasma sheet and associated with the field rotation ara large fluctuations in the field. The response of the field at 8 R/sub E/ was simultaneous with the ground onset, whereas further back at 11.3 and 2.4 R/sub E/ above the expected neutralmore » sheet the largest changes were delayed by 15 min. (auth)« less