POPULATION OF THE NEAR-EARTH MAGNETOTAIL FROM THE AURORAL-ZONE

This paper reports the development and performance of a large scale ki netic simulation using a three-dimensional model of the terrestrial el ectric and magnetic fields in an effort to reach a better understandin g of the ionospheric contribution to the near-Earth (x < 10 R(E)) regi on during quiet and slightly disturbed times. The simulation employed the Tsyganenko [1989] magnetic field model and an electric field deriv ed from the Heppner and Maynard [1987] ionospheric potentials. For the conditions considered in this study (southward interplanetary magneti c field (IMF), (phi(XT) = 20 - 40 kV), it was found that the cleft ion fountain plays a relatively minor role in supplying particles to the near-Earth region. The ionospheric contribution to the near-Earth prot on population is significant during quiet times with the bulk of the O + ions in the near-Earth region coming from the auroral zone upwelling region. However, the plasma mantle becomes the dominant hot proton so urce during more active times. Using the nightside auroral zone as a s ource, we launched distributions of H+, He+, and O+ ions and calculate d densities, pressures, and other bulk parameters in the near-Earth pl asma sheet and partial ring current. Because of the static nature of t he model, ionospheric ions had very limited access to the trapped ring current, but the ions formed a reservoir of energetic particles just outside this region that in theory could act as a source for the ring current during more active times. The residence time of ions in the mo del is too short for charge exchange losses to become significant, and the principal loss mechanism is through the dusk flank of the magneto pause, with precipitation into the ionosphere playing a minor role.