Thin Ionization Layer of the Enhanced Aurora

Princeton University, Princeton NJ

Investigators

Abstract

Nearly half of the time, auroral displays exhibit thin, bright layers known as "enhanced aurora." These displays are associated with thin, dense, heavy ion layers in the E-region. They result when wave-particle interactions heat ambient electrons to energies at or just above the 17 eV ionization energy of diatomic nitrogen. There are several possible plasma instabilities that could produce suprathermal electrons in thin layers, but there has been no detailed theoretical investigation of how instabilities in the thin ionization layers develop. This project will examine instabilities which would occur in thin, dense, heavy ion layers. It will use extensive analytical analysis combined with particle simulations. A preliminary analysis of a cross field current instability has been found to be strongly unstable in the heavy ion layers. Initial electrostatic simulations show that substantial heating of the ambient electrons occurs with energization at or above the nitrogen ionization energy. Further improvements in the model will lead to precise comparisons with observations, using a variety of data including ground based optics, radar measurements, and in situ rocket measurements. The model will also be used to examine other competing instabilities, so that the mechanism for the enhanced aurora can be established. The theoretical work and simulation code described in this proposal is also likely to have applications to instabilities associated with impurities in fusion devices where heavy ion species originating from the wall and limiter materials are known to contaminate the core hydrogen plasma.