Outward flow of plasms in the magnetotail following geomagnetic bays

Abstract

A study of electrons in the earth's magnetosphere, measured by the Vela 2 satellites, and of magnetograms from high-latitude stations on the earth has revealed that hot plasma containing electrons of energy >45 kev often arrives suddenly in the plasma sheet of the magnetotail at the peak or during the recovery phase of a negative magnetic bay in the auroral zone. It is found also that if a satellite is in the plasma sheet at the time a negative bay starts, it is likely to detect a decrease in the intensity and/or the average energy of the electrons there as the depth of the bay increases. These observations suggest that a contraction of the plasma sheet occurs during the development of a bay, followed by a sudden expansion starting at the beginning of bay recovery. It is concluded that the bursts of hot plasma in the magnetotail derive their energy from processes occurring inside the Vela satellite orbit (radial distance ∼17 RE). The relevance of these observations to models of the magnetosphere is discussed.