A numerical model for auroral precipitation

A numerical simulation model is used to show that the velocity distribution function of electrons responsible for the discrete aurora is modified by two processes: (1) In the region above the ionosphere, electrons are accelerated by a dc potential drop that extends from the plasma sheet to the topside ionosphere. In this region the number of particles per unit length in a magnetic flux tube increases with altitude. The simulations also show that electrons will be accelerated to higher energies on field lines with low plasma density. (2) When the accelerated electron beam encounters the ionospheric plasma, wave‐particle interactions occur. When the plasma density is a function of the coordinates perpendicular to the magnetic field, upper and lower hybrid waves are excited, which heat the electrons perpendicular to the magnetic field. Upper hybrid waves produce rapid perpendicular heating, which leads to large perpendicular gradients in the upward flowing parts of the electron distribution function, which in turn would enhance growth rates in auroral kilometric radiation. Linearized analysis of growth rates of upper and lower hybrid waves are presented to assess the likelihood that upper hybrid waves play a significant role in auroral processes.