Radar Interferometer Observations and Theory of Plasma Irregularities in the Auroral Ionosphere
Abstract
The radar interferometer technique first used at the equator in Peru is also a very powerful means for studying auroral plasma instabilities. It is shown to be a very useful tool for probing the essentially two-dimensional turbulence associated with the auroral plasma instabilities. The horizontal interferometer successfully measured the transverse vector electron drift velocities and the electric fields associated with radio aurora and visual discrete auroral arcs. The technique works well for a variety of radar auroral echoing types including diffuse with structure and discrete. The interferometer observations generally show that separate echoing regions within the scattering volume are responsible for composite spectra (e.g. type I and type II spectral features occurring simultaneously within the same spectrum). Kilometer scale ((lamda) (TURN) 50 km (+OR-) 20 km) wave-like structures are often observed along the radar line-of-sight during intense magnetic storms (K(,p) > 6). Quasi-periodic temporal variations in the horizontal drift velocity and in the mean Doppler shift of the power spectra have also been observed, and these appear to be associated with Pi micro-pulsations and perhaps kilometer scale gradient drift waves. A new spectral type, referred to here as type IV, has been identified and is shown to be probably a type I spectrum with an unusually large Doppler shift from a region where the local ion acoustic speed is much larger than normal, due to enhanced electron temperatures caused by anomalous plasma wave heating in the auroral electrojet. A linear fluid theory of plasma waves in the auroral E region is developed to set the framework for understanding the generation mechanisms for radar aurora. The linear theory is extended to long wavelengths as well as to a parameter regime characteristic of the upper E region, where ion magnetization effects are important. The general dispersion relation includes the effects of cross-field and field aligned drifts, ion inertia, electron density gradients, recombination, divergence in the ion flow, and parallel propagation. The significance of upper E region waves in light of observations of electrostatic ion cyclotron waves is emphasized. A new kinetic theory for collisional ion cyclotron waves is presented that extends the fluid linear results to wavelengths for which kR(,i) > 1.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1985
- Bibcode:
- 1985PhDT........57P
- Keywords:
-
- WAVES;
- ION CYCLOTRON;
- E REGION;
- Physics: Atmospheric Science