May 2002 General Meeting Report
Space Weather and the TIGER Radar.
Professor Peter L. Dyson
Department of Physics, La Trobe University.

It was a pleasure to welcome back Professor Peter Dyson, who some 2 2 years ago gave us a remarkable insight into the nature of space weather and its impact on Earth. After a quick hop-skip-and-jump through some basic physics and the origin of solar wind and its interaction with the Magnetosphere, on hand of a professionally prepared PowerPoint presentation (the computer worked flawlessly this time) Peter Dyson steered us to his favourite subject TIGER, an acronym that stands for Tasman International Geospace Environment Radar.

The Tiger concept is two Aover the horizon radar@ stations with beams intersecting at a specific angle that can cover the vast ocean area between the continental landmasses of Australia and New Zealand and the Antarctic. Its prime function is to locate aurora regions and measure motion caused by electric fields. The first of these stations is on Bruny Island south of Tasmania, which has been operational since December 1999. The second Station is going to be on the southern-most end of New Zealand with the centre of their radar beams intersecting approximately halfway down to the Geomagnetic Pole. This pattern can theoretically blanket an area of 10 degree radius around the pole, where most of the solar wind particles, guided by the Earth=s magnetic field lines, enter the atmosphere.
Over-the-horizon radar is not as straight forward a process as it sounds. Capable of detecting targets up to 3000km away, it depends though on multiple reflection between the Ionosphere and the surface of the Earth (or ocean), both of which can be in relative motion to each other. From early radio days it is well known that the density and electric properties of the Ionosphere, which extends from around 100km to a height of 350km, not only fluctuate with day and night and temperature, but are not consistent throughout its several layers. On top of this large ocean waves affect the angle of radio wave reflection. The radar stations can vary their frequencies between 8 and 20 MHz to adapt to and follow favourable propagating conditions. Optical and satellite monitoring of sphere density also helps to arrive at data reasonably consistent.

The information collected by the system will, apart from location ships and aircraft and auroras, help in predicting with greater accuracy dangerous radiation levels in the solar wind, resulting from erupting solar prominences, and give a direct measure of solar storms and their effect on the Earth environment. So confident are the people associated with the system of it=s potential benefits that the next generation of TIGER is already on the way, called SUPERDARN, for Super Dual Auroral Radar Network. It consists of a series of multiple intersecting radars covering the whole of Antarctica, capable of giving complete horizontal velocity vectors. Each pair of OTH Radars will swing through 16 beams in two minutes, measuring echo range and line of sight Doppler shift.

Time was not long enough to deal adequately with all the aspects of the fascinating subject. What about the mysterious AWhistler@ electrons, oscillating along the Earth=s magnetic lines of force? Or the study of the structure of the Plasma-sphere and its effects on GPS accuracy, done by Dr. Elizabeth Essex? It looks as though Peter Dyson has to come back again in this evolving narrative of space weather.