Magnetic field perturbations in the magnetotail associated with polar magnetic substorms

Abstract

Using data from the IMP-A and IMP-B satellites, it is shown that when a polar magnetic substorm onset is observed at the earth's surface, there is a pronounced effect in the magnetotail at approximately the same time. This magnetotail perturbation appears as a temporary reduction in the tail field reflecting primarily a reduction in the component of the field pointing along the sun–earth line parallel to the neutral sheet. Large perturbations in the component of the magnetic field perpendicular to the ecliptic plane which are observed around 24RE suggest that reconnection of magnetic field lines is the physical mechanism responsible for the observed effects. It is suggested that substorms act as a safety valve limiting the size of the magnetotail by periodically bleeding magnetic flux from the tail into the inner dipole configuration.