Lightning Current Parameters, Correlated Electromagnetic Fields and Digital Images of Lightning Discharges to the Gaisberg Tower

In Austria about 100.000 to 200.000 lightning strikes to ground are registered every year. Lightning causes annual damages of several tens of million of Euros. In the past lightning protection was mainly focused an personal safety and the avoidance of lightning caused fires. Overvoltage protection becomes more and more important as a result of today`s extensive use of sensitive electronic equipment. Lightning discharges are impulse currents of amplitudes up to 200.000 A associated with an intense electromagnetic field pulse. On the one hand this radiated field pulse is used to locaie lightning discharges with lightning location systems; an the other hand it may damalte electronic equipment up to distances of several hundred meters from the striking point. The detailed physical processes occuring within the lightning channel are still unknown and not accessible to direct measurements. At the best we can measure ihe lightning current at ground level but not at a given height. Since 1998 the radio tower at Gaisberg near Salzburg is instrumented for direct lightning current measurement. Ort average data from 50 - 60 lightning strikes are collected an that site every year. Worldwide there are only a very few comparable experimental sites for direct lightning measurements, like ihe CN tower in Toronto, a chimney of 200m height in Japan and a tower in Brazil. Simultaneous measurements of current and electromagnetic fields at various distances of the same flash is one of the best approaches to gather information about the processes along the lightning channel. Those measurements require fast digitizers with large data storage capability and a precise time synchronization of the distant recording stations. Today GPS satellite synchronized clocks and the commercially available digitizers allow performing such measurernents in the field of basic lightning research.