whole_CravenMichael1985_thesis.pdf (8.6 MB)
Pulsating aurora and magnetic Pi(c) pulsations
thesisposted on 2023-05-27, 00:44 authored by Craven, M.(Michael)
This thesis is the result of a year spent at Macquarie Island (54¬¨‚àû 30'S, 158¬¨‚àû57'E) on the 1983 Australian National Antarctic Research Expedition, collecting data pertaining to pulsating aurora and geomagnetic Pi(c) micropulsations. Data was collected with a 0.2s sampling period and stored by an LSI-11 microcomputer on floppy disks for the bulk of the year, then on RLO2 hard disk for the final months. Strong peak-to-peak correlations were observed between the optical pulsating aurora, measured at the N2+ 4278A band head emission, and the micropulsations. Average time delays were determined to be 0.6s and 0.3s for the D and H Pi(c) micropulsations respectively, trailing the optical fluctuations. The H component Pi(c) micropulsations will be shown to be consistent with a precipitation induced Hall conductivity enhancement of the westward E-region auroral electrojet during the greater part of this activity. The sign, or phase, of the 4278A/H micropulsation correlation function was in close agreement with the large scale magnetogram H component perturbation. The D component Pi(c) have in the past been interpreted as either an E-region Pedersen conductivity induced variation, or a direct field aligned current effect. Their correlation sign, or phase, is shown to be not in accord with the large scale D component magnetograms which are known to be effected by other than E-region currents, namely the field aligned fluxes.\ The D micropulsations are more frequently correlated at an acceptable level with the optical emission and their correlations are in general of greater magnitude than those of the H Pi(c). Experimentally observed lack of a frequency doubling in the micropulsations with respect to the optical trace occasional phase reversals of the correlations and the delay sequence wherein the optical pulses predominantly lead the H micropulsations which in turn generally lead the D component can all be reasonably explained in terms of the above theories. A model has been developed involving rotations of the total ionospheric electric field which makes basic predictions concerning the phases of the correlations and the lead-lag relationship between the micropulsation components. These predictions are borne out by the data set specifically during phase reversals and strongly indicate that the H and D Pi(c) micropulsations result from precipitation induced conductivity fluctuations in E-region current systems."
Rights statementCopyright 1985 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (M.Sc.)--University of Tasmania, 1985. Bibliography: leaves 216-226