Lightning is an atmospheric phenomenon that has interested, amazed, and sometimes terrified people for millennia. From an engineering point of view, it is one of several destructive agents created by our atmosphere, and one that can cause damage to many types of structures and systems. The investigation of lightning and its effects described in this thesis was carried out between about 1960 and 2008 mainly in south-east Queensland, Australia. The damaging effects of lightning provide a strong motivation for studying lightning protection techniques for structures and systems. Prediction of the frequency of lightning events to or near a structure or system should determine what protection is necessary, and this will require an estimate of the ground flash density (GFD) (lightning flashes to ground per km2 per year). When this investigation commenced, the GFD was poorly known for Australia. Estimation of the probability of injury to people or damage to a structure or equipment also requires knowledge of other lightning characteristics, including their electric and magnetic fields, and stroke current magnitudes and waveshapes.
A significant effort was therefore directed toward means of measuring the GFD, and this led to the study of lightning flash counters (LFC). These are low-cost devices that can be deployed in sufficient numbers over a region to obtain information about GFD. Some early types of LFC were trialled, mainly in or near Brisbane, Queensland, including the Pierce- Golde LFC developed in the UK. Studies of the field performance of this and other LFCs in the 1960s revealed certain deficiencies, in particular, an unwanted response to cloud flashes. It was found necessary to establish the effective range so that annual counts could be converted to GFD, and to investigate aspects of the physics of ground and cloud flashes as well as their frequency of occurrence. It was found that the time variation of electric field at an observation point caused by a remote lightning flash , known as the electric field change (EFC), was the single most useful type of observation for providing the required information. The time variation of optical radiation from the flash was also studied, but was found to be less useful than the EFC in providing information about physical processes, and less likely to lead to improvements in LFC design.
In developing a new form of LFC that overcame some of the deficiencies of other types, attention was directed towards applying pattern recognition techniques to the EFC as the main source of information about the lightning event, and by using the information provided by the concurrent investigation of the physical characteristics lightning. It was intended that the effective range of the instrument should be more readily determined than for the earlier types of LFC, and that the instrument should provide information about the relative numbers of cloud and ground flashes. The resulting instrument in the 1980s was denoted the CGR3. Several of these were distributed to interested persons both overseas and in Australia, who operated them and provided lightning occurrence information over a latitude range about 60°N to 27° S, providing the basis for a study of the latitudinal variation of lightning occurrence, in particular, the variation of flash density and the cloud flash-to-ground flash ratio with latitude. In the 2000s, to meet a requirement by the Australian Bureau of Meteorology for a lightning sensor suitable for future installation in their Automatic Weather Stations, an improved version of the CGR3, denoted CGR4, was developed. Lightning investigations from 2000 on have focused mainly on testing and improving the CGR4.
In the 1990s, satellite-based global lightning surveys became available, and, in cooperation with researchers in the USA, it became possible to combine the results of the survey using CGR3 instruments with the satellite surveys to produce a global model of lightning occurrence, including diurnal and annual variations. This combined information, together with oceanic surveys of the Earth's ocean surface electric field carried out early in the 20th century, enabled a study of the contribution of global lightning to the ionospheric electric charging process to be carried out.
A NASA satellite survey of lightning in the 2000s was combined with Australian total flash density information from CIGRE 500 Hz and CGR3 lightning flash counters, to produce the first total flash and ground flash density maps for Australia. This enabled a ground flash density estimate to be made for any part of Australia, removing the need to estimate GFD from the local annual thunderday level, and assisting in predicting the need for lightning protection of structures and systems, and in the assessment of personal safety during thunderstorms.