Associate Professor Neil Thomson

The Earth's upper atmosphere intercepts important electromagnetic and fast particle radiation from the Sun and beyond, giving protection for life below. This radiation also ionizes the upper atmosphere allowing long-distance radio communication and providing a way to monitor changes in the incoming radiation. In particular, the lowest edge of this ionization, at heights 50-90 km (depending on time of day etc) forms the upper level of the Earth-ionosphere 'waveguide' (bounded below by the ground). Very Low Frequency (VLF) radio waves, both natural (eg lightning) and man-made, propagate in this waveguide. Their readily measured propagation is very sensitive to the height and sharpness of the waveguide ceiling. These, in turn, are very sensitive to many changes: solar flare x-rays, gamma-ray bursts, fast particle precipitation, cosmic rays, day-dusk-night-dawn, latitude, season, solar cycle etc.

My research interests are centered on measuring and understanding these effects, most recently concentrating on the quiet earth-ionosphere waveguide height and sharpness which provides the reference baseline for all these changes. This involves experimental observations both here and around the word, together with the modeling of the results and their underlying physics.

I also have research interests at greater heights, in the Earth's plasmasphere (~ 10,000 km altitude) which again involve radio propagation both observational and modeling (ray tracing).