Adiabatic motion of auroral particles in a model of the electric and magnetic fields surrounding the Earth

The motion of charged particles in the electric and magnetic fields constituting the earth's magnetosphere is calculated using the assumption that the first and second adiabatic invariants are conserved. The model of the magnetic field includes the effects of the solar wind pressure on the sunward side of the magnetosphere and of the newly discovered current sheet in the magnetospheric tail. The electric field is deduced in the ionosphere from the SD current system which accompanies magnetic bays. The magnetic field lines are then assumed to be equipotentials, so that the electric field can be projected throughout the magnetosphere. The motion of low energy plasma is discussed qualitatively, and the motion of solar wind particles which become trapped on the surface of the magnetosphere is calculated in quantitative detail. It is found that solar wind electrons (kinetic energy at the magnetospheric surface <1 kev) will be accelerated to energies in the range of 1 to 40 kev and will be confined to a narrow latitudinal zone where extensive precipitation into the atmosphere will occur during local nighttime. Protons of similar energy will be confined to a region south of the electron region and will precipitate during local afternoon and evening. The conclusion is reached that auroral events are produced largely by electrostatic acceleration of solar wind particles and occur on lines of force which close in the tail of the magnetosphere within 50RE of the earth.