Core plasma in the magnetosphere

The “core” of magnetospheric plasma distribution functions is of prime importance in the magnetospheric plasma behavior. For the purposes of this review and because of recent instrumental characteristics, we shall regard the term “core plasma” to include ions and electrons with energies less than 50 eV. In the period 1983–1986, several new and important core plasma phenomena and regions have been identified, including: the cleft ion fountain, the plasmaspheric heavy ion torus, core molecular ions, high core plasma densities in the plasma sheet boundary layer, intense transverse heating of core plasmas in the equatorial regions, the low‐energy ion transition (LEIT) delineating the plasmaspheric and plasma sheet regions, the supersonic polar wind, toroidal or ring heavy ion distribution functions in the auroral region, conic‐to‐field‐aligned ion signatures of inverted V auroral events, and large‐scale electron density structure in the magnetosphere. On the theoretical/modeling side, significant progress has been made on: the effect of hot electrons on the polar wind; simulation of thermal helium heating at the equator; kinetic models of the plasma transport from localized ionospheric regions; time‐dependent hydrodynamic models of the polar wind and plasmasphere‐ionosphere coupling; studies of the behavior of the plasmaspheric He + , O + + and counterstreaming He + ‐H + ; and kinetic models of plasmasphere refilling. In this report, we shall briefly review the progress during the past quadrennium in these and other topics under the general headings: (1) core plasma in the plasmasphere and plasmapause region, (2) core plasma in the polar cleft and polar cap magnetosphere, and (3) core plasma in the auroral and plasma sheet magnetosphere.