Thin Ionization Layers and Enhanced Aurora Current

Project Description:

Nearly half of the time, auroral displays exhibit thin, bright layers known as ``enhanced aurora.'' There is a substantial body of evidence that connects these displays with thin, dense, heavy ion layers in the E-region. Based on the spectral characteristics of the enhanced layers, it is believed that they result when wave-particle interaction heats ambient electrons to energies at or just above the 17 eV ionization energy of N2. While there are several possible instabilities that could produce suprathermal electrons in thin layers, there has been no clear theoretical investigation which examines in detail how wave instabilities in the thin ionization layers could develop and produce the suprathermal electrons. This task is the aim of this project.

We plan to examine instabilities which would occur in thin, dense, heavy ion layers using extensive analytical analysis combined with particle simulations. In the proposed research section, we present preliminary analysis of a cross field current instability that is 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 N2 ionization energy. Further improvements in the model should lead to more precise comparison with observations. The proposed model may also be used to examine other competing instabilities, so that the mechanism for the enhanced aurora can be established.

Principal Investigator:

Jay R. Johnson
Princeton University

Co-Investigator:

Hideo Okuda
Princeton University

Collaborator:

Dirk Lummerzheim
Univerisity of Alaska

The following presentations describe the progress of this project:

Cross-Field Current Instabilities in Thin Ionization Layers and the Enhanced Aurora (pdf file) To be submitted to Journal of Geophysical Research

Enhanced Aurora and Instabilities in Thin Ionization Layers--- (pdf file)

This project is supported by NSF Grant ATM-0411392
  Jay R. Johnson / jrj@pppl.gov/243-2603