The role of the Hermanus Magnetic Observatory in geomagnetic field research

Abstract

A b s t r a c t . Geomagnetic field research carried out at the Hermanus Magnetic Observatory over the past decade is reviewed. An important aspect of this research has been the study of geomagnetic field variations, with particular emphasis on ULF geomagnetic pulsations. Features of geomagnetic pulsations which are unique to low latitude locations have been investigated, such as the cavity mode nature of low latitude Pi 2 pulsations and the role played by ionospheric O + ions in the field line resonances responsible for Pc 3 pulsations. A theoretical model has been developed which is able to account for the observed relationships between geomagnetic pulsations and oscillations in the frequency of HF radio waves traversing ionospheric paths. Other facets of the research have been geomagnetic field modelling, aimed at improving the accuracy and resolution of regional geomagnetic field models, and the development of improved geomagnetic activity indices.K e y words: Geophysics, geomagnetic field. IntroductionThe Hermanus Magnetic Observatory (HMO) had its origin during the Second Polar Year 1932-1933, an international cooperative project conceived to gain a better understanding of the Earth and its environment. Thus the HMO began its existence due to man's quest for scientific knowledge and understanding. Over the years, however, the prime objectives and culture of the HMO have changed. Particularly significant changes occurred after 1986 when the CSIR, of which the HMO forms part, was reformed to become a more market oriented organisation with the prime objective that research results should be implemented for the benefit of South African industry and society.Over most of the past decade the HMO has functioned primarily as a service providing and technology development body. The service provision aspect entails the provision of information and data on the geomagnetic field to clients mainly for use in the fields of navigation and geophysical exploration. Notwithstanding these changes, the HMO still finds it essential to carry out fundamental and applied research, albeit at a reduced level compared to earlier years.In this paper research carried out at the HMO since 1986 is reviewed. The work falls into three main categories, namely, the study of geomagnetic variations of various types, geomagnetic field modelling, and geomagnetic activity indices. Geomagnetic Field VariationsA variety of temporal variations, spanning periodicities from fractions of a second up to millions of years, take place in the Earth's magnetic field. Studies at the