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SILICON SILIC CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc. (Hons.) Technical Editor John Clarke, B.E.(Elec.) Technical Staff Ross Tester Jim Rowe, B.A., B.Sc Nicholas Vinen Photography Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst David Maddison B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Kevin Poulter Dave Thompson SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Offset Alpine, Lidcombe, NSW. Distribution: Network Distribution Company. Subscription rates: $105.00 per year in Australia. For overseas rates, see our website or the subscriptions page in this issue. Editorial office: Unit 1, 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Recommended & maximum price only. 2  Silicon Chip Publisher’s Letter The visual spectacle of thunderstorms and auroras Ever since I was a young boy, I have been fascinated by thunderstorms and their visual spectacle. Indeed on many a stormy night at home I love to go upstairs, open up all the blinds and watch the show. Our home has panoramic views over the sea and the show can often be spell-binding as I watch vast cloud formations flicker and flash, often lighting up the sea and coast as bright as day. And while many people would probably refer to these displays as “sheet lightning” (if they think about them at all), they are far more than that. Yes, the cloud formations do light up and flicker from one cloud to the next but that is partly because the direct lightning strikes are obscured from view by the clouds themselves. But if you look more closely you will often see that most of these strikes are visible, whether from cloud to ground or from cloud to cloud. And often those cloud to cloud strikes themselves are truly spectacular, especially when you realise that they can easily span a distance of 20km or more. And then there are strikes which don’t appear to hit the ground at all but merely spear off into the distance or even straight up into space. How does that work? We now know that what we see of thunderstorms is only a small part of the show and that for every discharge to earth, there are equal discharges out into space, far, far, above the stratosphere, as described in our feature article on Atmospheric Electricity by Dr David Maddison, in this month’s issue. But the spectacle of a thunderstorm is even more amazing when you realise that the light show is continuous and lasts for many hours. In truth, a big storm can last for days. I will often go to bed in the evening while a thunderstorm is raging outside and then get up in maybe five or six hours later and the storm will still be visible far out to sea or even beyond the horizon, maybe more than 100km to the east. And if I bothered to follow it on the Bureau of Meteorology’s weather radar, I could still see the storm several days afterwards until it petered out maybe 1000km away. All that time, there would have been many thousands of lightning strikes per hour; no wonder the light show is continuous! And of course, the evidence of all that electrical activity is not confined to the immediate locality of the thunderstorm which may easily range over an area of more than 100 square kilometres or a great deal larger. In fact, it is merely a tiny part of the global electrical circuit (GEC) and every lightning strike has effects which ripple right around the planet. And then we read in this month’s issue about Schumann resonances (between the surface and the ionosphere) and how those resonances are triggered by lightning strikes. Think of that – the GEC ringing like a bell due to lightning and that is happening all the time, around the world. And it has been like that for billions of years! And the GEC itself is heavily influenced by the Sun and the most visible evidence of that is in the auroras which are visible over vast areas of the polar regions. No wonder there is growing tourism to view those wonderful spectacles. And then think about the Sun-induced violent geomagnetic storms. They utterly dwarf our Earth-bound storms and can have far more reaching effects as well. With all that to consider, the ancients were right to tremble as the power of storms was unleashed upon them. Yet they did not know even a fraction of what was really going on, just as we today do not fully understand the mechanisms of storms. What we do know is truly enthralling and mind-boggling. Next time a storm is brewing, even before it arrives in your locality, take the opportunity to watch and wonder. Be enchanted. Leo Simpson siliconchip.com.au