SPACE PLASMA THEORY

High Latitude Ionospheric Modification by Radio Waves
Gondarenko, Guzdar

The artificial generation of large and small-scale ionospheric irregularities using HF-heaters can impact a variety of space and ground-based communications, navigation, and surveillance systems. The understanding of the generation of these irregularities is thus a key objective. One mechanism that can create the irregularities is the thermal self-focusing of the high-powered heater waves. Over the last few years we have developed a 2D nonlinear code which investigates the spatio-temporal development of such irregularities. In the accompanying figure we show the development of the heater wave (left panels), the electron temperature (middle panels) and the plasma density (right panels) at t = 5.6s near the reflection height of a linearly stratified ionosphere. The heater wave generates the irregularities by the process of thermal self-focusing near the critical height and the irregularities, diffuse along the magnetic field lines (vertical direction) producing the field aligned structures. The goal of our studies is to investigate the spectrum of these irregularities for different ionospheric conditions and different polarizations and power density of the heater wave.

This research is supported by the National Science Foundation and the Office of Naval Research.

3D Simulation of the Dynamics of High Latitude Plasma Patches
Gondarenko, Guzdar

The ionospheric plasma at high latitude is known to display varied characteristics. During the phase when the interplanetary magnetic field is southward, large scale plasma patches/blobs, typically hundreds of kilometers, are formed in the cusp region and convect to the polar cap over periods of several hours. These patches are seen to have small scale irregularities, which are typically ten to a hundred times smaller than the size of the patch. We have developed a three-dimensional code for the plasma patch to gain an understanding of this meso-scale structuring. Earlier two-dimensional simulations showed that the structuring would lead to rapid fragmentation of the patch, contrary to observations. Introduction of the third dimension along the earth's field line causes the long wavelength instabilities to be stabilized. Thus this work will hopefully lead to a more complete understanding of the selection of the scalelengths of the structuring in the nonlinear phase and better agreement with observations.

The top figure shows five isosurfaces for the initial patch, with the peak density in red. After about an hour the patch develops irregularities (shown in the lower figure) due to the gradient drift instability and secondary Kelvin-Helmholtz instabilities.

This work is supported by the National Science Foundation.