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Rain imminent
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THE LAST WORD Rain imminent During the 2008 Monaco Grand Prix, I was watching the drivers battle with the damp conditions when the commentator said that rain was expected at the track in 6 minutes. How can forecasting be so accurate? If such technology is available, why isn’t it offered to the public? Incidentally, the rain didn’t arrive on this occasion, but was predicted with such confidence that presumably the forecasting must be accurate most of the time.
Many readers thought the answer was probably weather radar. The US, Australia the Netherlands and Germany all appear to have publicly available services. Here’s a typical example… ■ I assume they use a weather radar. We have one sited 200 kilometres to the west of us, at West Takone, Tasmania, and by checking on the Australian Bureau of Meteorology website we can see a real-time picture of where the rain is falling and how heavy it is, or a loop showing how fast the rain is moving towards us. Great for getting the washing dry. When our roof collapsed in the middle of winter and we were living under tarpaulins, it was wonderfully useful. The builders kept an eye on the weather radar,
■ The reason we can achieve such accuracy in forecasting at each grand prix is because we have radar and weather stations on-site provided by the the FIA, the governing body of world motor sport. In Monaco, these are operated by the French “We can see a real-time meteorological office, Météo France, which has an experienced picture of where the rain forecaster on-site to predict when is falling or how fast it is moving towards us” inclement weather will arrive. Each racing team is offered a subscription to the service, which and when there looked to be at is then fed to the team’s timing least 20 minutes clear they would stand at the trackside. This displays whip off the tarps and work until radar images, temperatures and I gave them a 5-minute warning pressures in near real time. There to put them back again. is also a minute-by-minute rain Jan Horton update provided via the trackside West Launceston, Tasmania TV feed system, which also Australia updates on-track events such as the blue warning flags waved at Misty morn cars about to be lapped. While camping in the desert north Joseph Birkett of Coober Pedy, South Australia, Trackside IT Engineer on 8 July 2007 my son and I were Red Bull Racing privileged to witness a white Milton Keynes rainbow at daybreak (see photo). Buckinghamshire, UK
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions, please send an SAE to LWQlist at the above address.
an aircraft, a fogbow can appear as an almost complete circle. Storm Dunlop Chichester, West Sussex, UK
The landscape was covered in mist and the white rainbow’s arc seemed to grow as the sun came up, though it faded away as the mist evaporated. I’ve asked old swagmen, indigenous locals and several lecturers at two universities, but no one has ever witnessed the phenomenon. What caused it?
■ This was a fogbow, sometimes known as a cloudbow or mistbow. Like a primary rainbow, it is centred on the point opposite the sun and has an angular radius of approximately 42 degrees. It is caused by the same mechanism: reflection and refraction of sunlight by water droplets. In this case the droplets are unusually small – less than 50 micrometres across –allowing diffraction to spread the bands of colours so that they overlap and appear white. Occasionally, fogbows will show a bluish tinge to the inner edge and a reddish one on the outer. From some viewpoints, such as
Do Polar Bears Get Lonely? A brand new collection serious enquiry, brilliant insight and the hilariously unexpected Available from booksellers and at www.newscientist.com/ polarbears
■ A fogbow is a frustrated rainbow, formed in essentially the same way. Sunlight destined to create rainbows and fogbows is refracted twice – once as it enters a water drop and again as it leaves. While inside the water drop between the two refractions, the light bounces off the inside back surface, sending it heading back towards the sun. This is why rainbows and fogbows are seen when the sun is behind the observer. The path of blue light is bent more than red by the droplet causing sunlight to be dispersed into the colours of the visible spectrum with blue at the bottom of a rainbow and red at the top. Rainbows appear white when water droplets are less than 100 micrometres across – small enough for diffraction to dominate over refraction. Each water drop forms its own diffraction pattern – bands of alternate constructive and destructive interference – for each colour: the smaller the drop, the broader the bands. When the drops are small enough, these bands become so broad that all the colours overlap, essentially mixing them all together again, to make white. Beautiful images can be found at www.atoptics.co.uk/droplets/ fogbow.htm. Mike Follows Willenhall, West Midlands, UK
THE LAST WORD Rain imminent During the 2008 Monaco Grand Prix, I was watching the drivers battle with the damp conditions when the commentator said that rain was expected at the track in 6 minutes. How can forecasting be so accurate? If such technology is available, why isn’t it offered to the public? Incidentally, the rain didn’t arrive on this occasion, but was predicted with such confidence that presumably the forecasting must be accurate most of the time.
Many readers thought the answer was probably weather radar. The US, Australia the Netherlands and Germany all appear to have publicly available services. Here’s a typical example… ■ I assume they use a weather radar. We have one sited 200 kilometres to the west of us, at West Takone, Tasmania, and by checking on the Australian Bureau of Meteorology website we can see a real-time picture of where the rain is falling and how heavy it is, or a loop showing how fast the rain is moving towards us. Great for getting the washing dry. When our roof collapsed in the middle of winter and we were living under tarpaulins, it was wonderfully useful. The builders kept an eye on the weather radar,
■ The reason we can achieve such accuracy in forecasting at each grand prix is because we have radar and weather stations on-site provided by the the FIA, the governing body of world motor sport. In Monaco, these are operated by the French “We can see a real-time meteorological office, Météo France, which has an experienced picture of where the rain forecaster on-site to predict when is falling or how fast it is moving towards us” inclement weather will arrive. Each racing team is offered a subscription to the service, which and when there looked to be at is then fed to the team’s timing least 20 minutes clear they would stand at the trackside. This displays whip off the tarps and work until radar images, temperatures and I gave them a 5-minute warning pressures in near real time. There to put them back again. is also a minute-by-minute rain Jan Horton update provided via the trackside West Launceston, Tasmania TV feed system, which also Australia updates on-track events such as the blue warning flags waved at Misty morn cars about to be lapped. While camping in the desert north Joseph Birkett of Coober Pedy, South Australia, Trackside IT Engineer on 8 July 2007 my son and I were Red Bull Racing privileged to witness a white Milton Keynes rainbow at daybreak (see photo). Buckinghamshire, UK
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions, please send an SAE to LWQlist at the above address.
an aircraft, a fogbow can appear as an almost complete circle. Storm Dunlop Chichester, West Sussex, UK
The landscape was covered in mist and the white rainbow’s arc seemed to grow as the sun came up, though it faded away as the mist evaporated. I’ve asked old swagmen, indigenous locals and several lecturers at two universities, but no one has ever witnessed the phenomenon. What caused it?
■ This was a fogbow, sometimes known as a cloudbow or mistbow. Like a primary rainbow, it is centred on the point opposite the sun and has an angular radius of approximately 42 degrees. It is caused by the same mechanism: reflection and refraction of sunlight by water droplets. In this case the droplets are unusually small – less than 50 micrometres across –allowing diffraction to spread the bands of colours so that they overlap and appear white. Occasionally, fogbows will show a bluish tinge to the inner edge and a reddish one on the outer. From some viewpoints, such as
Do Polar Bears Get Lonely? A brand new collection serious enquiry, brilliant insight and the hilariously unexpected Available from booksellers and at www.newscientist.com/ polarbears
■ A fogbow is a frustrated rainbow, formed in essentially the same way. Sunlight destined to create rainbows and fogbows is refracted twice – once as it enters a water drop and again as it leaves. While inside the water drop between the two refractions, the light bounces off the inside back surface, sending it heading back towards the sun. This is why rainbows and fogbows are seen when the sun is behind the observer. The path of blue light is bent more than red by the droplet causing sunlight to be dispersed into the colours of the visible spectrum with blue at the bottom of a rainbow and red at the top. Rainbows appear white when water droplets are less than 100 micrometres across – small enough for diffraction to dominate over refraction. Each water drop forms its own diffraction pattern – bands of alternate constructive and destructive interference – for each colour: the smaller the drop, the broader the bands. When the drops are small enough, these bands become so broad that all the colours overlap, essentially mixing them all together again, to make white. Beautiful images can be found at www.atoptics.co.uk/droplets/ fogbow.htm. Mike Follows Willenhall, West Midlands, UK