Studies of magnetic micropulsations with special reference to discrete emissions in the vicinity of one cycle per second
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The work on magnetic micropulsations described in this thesis falls into two parts. The first part considers micropulsations associated with meteoric phenomena, a high-altitude thermo-nuclear explosion, and man-made electromagnetic interference.
In the study on the association of micropulsations with meteors, both the effects of hourly meteor rates and individual meteor occurrences on micropulsation activity in the 1.5 cps band recorded at the same site, are considered. It is found that the variation in hourly meteor rates, plotted through a succession of nights, is not significantly related to the corresponding micropulsation activity. Most individual meteors do not have any associated micropulsation activity, but the number of coincidences is greater than random, and it remains possible that some of the larger meteors do produce magnetic effects.
Observations of the magnetic disturbance produced by the July 9, 1962 thermo-nuclear explosion above Johnston Island are described and the characteristic oscillation periods are interpreted.
In the second part of the thesis, the development of recording and data analysis instrumentation, suitable for observing the frequency-time properties of signals in the Pc1 band (0.2 - 5 cps), is described and the characteristics of eight months of recorded data are interpreted in order to gain insight into the origin of the discrete Pc1 emissions generally known as pearl-type micropulsations or hydromagnetic emissions.
Special attention is given to the design of a galvanometer-photocell preamplifier and it is shown that the frequency response of a standard laboratory galvanometer may be extended, by the application of feedback, to cover a considerable portion of the Pc1 band.
The fine structure properties of hydromagnetic emissions are found to be in qualitative agreement with recently suggested theories for emission propagation by hydromagnetic ion cyclotron wave packets in the magnetosphere. Significant diurnal variations in hydromagnetic emission fine structure parameters are established, and it is shown that these are not associated with the daytime attenuation of hydromagnetic waves in the ionosphere, but with the emission source in the magnetosphere. The diurnal variations indicate that the emission source is located near the L=4 field line between 03 - 06 hr LT, and near the L=6.5 field line between 12 - 15 hr LT. The diurnal movement in the emission source position provides a simple explanation for the variation in hydromagnetic emission diurnal occurrence with latitude, and is also consistent with the variation in average emission frequency with latitude. It is suggested that the diurnal movement in the source position may result from the magnetospheric convection of low energy trapped particles.
A preliminary analysis of the effects of geomagnetic activity on hydromagnetic emissions shows that the average nighttime location of the emission source is in the vicinity of the L=5 field line on extremely quiet days, and the L=3.7 field line on moderately disturbed days.