Radio and optical studies of natural and artificially stimulated geospace plasmas

Ashrafi, Mina (2006) Radio and optical studies of natural and artificially stimulated geospace plasmas. PhD thesis, Lancaster University.

Abstract

Results from radio and optical observations of natural and artificially enhanced geospace plasmas are presented. Firstly, naturally occurring plasma phenomena was studied by means of the radio and optical ground-based instruments and the results are compared with the in-situ satellite measurements. Observations of auroral absorption combined with auroral optical data provide information about characteristic energies of precipitating electrons. The energies recorded using the ground-based instruments are compared with the DMSP satellite data recordings during geomagnetic conjunctions. Results of this investigation indicate there is good agreement between the satellite Maxwellian spectra and the characteristic energies derived from the ground-based measurements when there is no ion precipitation and geomagnetic condition is moderate. Secondly, artificially enhanced ionospheric plasma by means of high power HF radio waves have been studied theoretically and experimentally. Radio observations indicate persistent descending of pump-induced enhancement in the UHF ion-line backscatter power. This effect has been modeled using electron temperature and density perturbation equations. It is concluded that a maximum electron temperature enhancement of up to ∼5700 K was achieved on average. Possible mechanisms and improvements to the model are discussed. The artificial optical rings were produced by pump-induced accelerated electrons. The optical emissions’ descent in height during each Heater-on cycle have been estimated by height triangulation from bi-static camera observations. The spatial evolution of the optical emissions, radar ion-line enhancements and stimulated electromagnetic emissions (SEE) spectra all show a similar altitude morphology. Typically, the optical height is close and below that of the radar backscatter, both of which are above the SEE generation altitude. Various radio and optical signatures of the artificially enhanced plasma are discussed. There is evidence that upper hybrid and Langmuir waves may act simultaneously to accelerate electrons causing the artificial optical emissions.