Energetic particle injections in the inner magnetosphere as a response to an interplanetary shock

The response of the magnetosphere to interplanetary shocks or pressure pulses can result in sudden injections of energetic particles into the inner magnetosphere. On August 26, 1998, an interplanetary shock caused two injections of energetic particles in close succession: one directly from the dayside and the other indirectly from the nightside associated with a sudden magnetic field enhancement induced by the shock's effect on the magnetotail. The latter injection was different from a typical substorm injection in that the nightside magnetic field at geosynchronous orbit enhanced almost simultaneously over a wide range of local times within 10 min after the arrival of the shock. Available observations and our simulations show that like the dayside, the nightside magnetosphere can also inject energetic particles into the inner magnetosphere from a wide local time region in response to a shock impact. The nightside particle injection was due to changes in magnetic and electric fields over a large region of space and thus shows that the magnetic and electric fields in the magnetotail can respond globally to the shock impact.