Very low frequency emissions from the exosphere
Creators: name: Dowden, RL
Publisher: name: University Of Tasmania
Year: 2023

description: This work describes investigations in a relatively new field: very, low frequency radio emissions from the earth's atmosphere. It is new in that most of the development has occurred in the last five or six years, though the phenomena has been known for some decades. Two basic types of emissions occur: continuous (hiss\) and discrete. When this work was begun in 1959 comparatively little was known about \"hiss‚ÄövÑvp though a considerable amount of information about the discrete emissions was obtained during the I.G.Y. The cause of either of these types was still a mystery though two theories (shown to be unlikely in this thesis) which seemed to explain some of the features of the discrete emissions appeared in that year. The dominant feature of this thesis is the doppler shifted (electron) cyclotron theory which is shown to explain all types of V.L.F. exospheric emissions. This idea occurred to the author while writing Chapter 4 (review of theories) after all the experimental work and Chapters 24 5 and 6 had been completed (late 1961). The development of this and other ideas and the general layout of the thesis are given below. Chapter 1. The present chapter mainly an outline of the rest of the thesis. Chapter 2. This brings the reader up to the present state of knowledge of the phenomena. The development of this knowledge is traced from the earliest to the present time. Except for some of the illustrations the author's contributions have been excluded. Chapter.3. The author's observations and experimental techniques are presented and discussed in this chapter. Only work on the continuous emissions was performed. Chapter 4. All the theories proposed (up till about 1961) for the generation of very low frequency emissions as well as some proposed by radio astronomers for high frequency generation are reviewed. The most promising idea seemed to be the travelling wave tube (TWT) process. A new idea suggested itself in discussion of doppler shifted cyclotron radiation from protons. These ideas are developed in later chapters. Chapter 5. Further development of these ideas first required a model of electron density distributions in the exosphere. A theoretical model based on geomagnetic control is derived in this chapter. Soon after this work was done (1960) experimental confirmation appeared. Chapter 6. Using this model Gallet's TWT process is treated in the general case and in more detail. It is show that this process can account for all the relevant characteristics of hiss though not those of the discrete emissions for which it was originally proposed. Chapter 7. The idea from Chapter 4 that cyclotron radiation from electrons is permissible if it is shifted down by doppler effect is developed. It is shown that this process gives the detailed frequency time characteristics of the discrete emissions. A new emission is predicted. Chapter 8. Four tests of this electron-cyclotron theory are presented. The most crucial of these was the observation of the predicted emission with the predicted time characteristics. Chapter 9. Since the frequency-time characteristics of observed discrete emissions could be accurately matched by suitably choosing the electron parameters (energy helical pitch and latitude) it seemed that these parameters could be deduced from observed characteristics. A method of doing this is presented with examples from published spectrograms of emissions. Chapter 10. It is shown in this chapter that this electron-cyclotron process can also account for the characteristics of hiss as well as does the TWT process (as developed in Chapter 6). Tests for distinguishing the two theories are proposed. Chapter 11. A brief resume of the progress achieved is given further work is suggested papers published by the author on this work are listed and acknowledgements are made."