Pulsating aurora and magnetic Pi(c) pulsations

• Main Author: Craven, M.(Michael)
• Format: Thesis
• Language: English
• Published: 1984
• Subjects: Auroras; Geomagnetic micropulsations; Antarctic; Pedersen; Strong Peak; Antarc*; Macquarie Island
• Online Access: https://eprints.utas.edu.au/19541/; https://eprints.utas.edu.au/19541/1/whole_CravenMichael1985_thesis.pdf

This thesis is the result of a year spent at Macquarie Island (54° 30'S, 158°57'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.