The detection and analysis of VLF triggered emissions.

The work described in this thesis consists essentially of two parts. The first is the design and development of/ ä rocket-borne
V. L. P. receiver for the observation of the magnetic field component
of electromagnetic waves in the frequency range 100 to 20,000 Hz.
The author's particular contribution was/ the optimisation of the design
of a smallμ-metal rod aerial. The approach was necessarily partly
empirical, partly theoretical. The former involved the systematic
adjustment of the number of turns, coil geometry, dimensions and type
of wire, etc. for the particular rod length small enough to be flown
in the space available in the rocket nose-cone. This was complemented
by a theoretical approach involving the rod and equivalent circuits
which satisfactorily reproduced the measured frequency response and
signal/noise properties of the aerial and preamplifier.
The second part of the thesis is concerned with the analysis and
interpretation of discrete V. L. F. emissions using the phenomenological
theory of Helliwell. Both medium and high latitude emissions were analysed
in detail. Significant advances were made in the computer iteration
techniques applied to the analysis of these emissions and limitations in
the analytical methods used were investigated in great detail. Particularly
interesting were several "slow risers" recorded at Andoya (L
= 6.6)
in northern Norway. The analysis determined the time varying energy
spectrum of the phase-bunched electrons giving rise to the emission
in the vicinity of the earth's equator (- 6.6 earth radii) for a rangeof possible equatorial ambient electron densities. It was possible
to determine an upper limit to the electron density at the equator
which, since it was in excellent agreement with that (2 to 5 electrons/
cc) determined by more direct measurements, provided new experimental
support for the theory. The limitations in the theory were examined
and a small error in the original formula of Helliwell corrected.