>From New Scientist, also abstract below. Article http://www.newscientist.com/article/dn20667-second-world-war-bombers-changed-the-weather.html Abstract http://doi.wiley.com/10.1002/joc.2392
Article Second world war bombers changed the weather 00:01 08 July 2011 by Michael Marshall For similar stories, visit the Histories , Climate Change and Aviation Topic Guides Allied bombing raids during the second world war inadvertently experimented on the weather by producing huge contrails over south-east England. A study of one 1944 raid offers a rare opportunity to check our models of how contrails change temperatures. After listening to a radio programme in which an elderly woman recalled seeing a wartime sky "turn white with clouds" as fleets of bombers took off, Roger Timmis of Lancaster Environment Centre in the UK realised that the planes could have affected the weather. Contrails are known to have several effects on climate. On the one hand, they act as a blanket, trapping heat that would otherwise escape into space. On the other, during the day they reflect incoming sunlight, cooling the Earth below more than it is warmed by the other effect. But overall, the consensus among climatologists is that they warm the planet. In the 1940s – unlike today – there was hardly any civilian air traffic, so historical records offer an opportunity to test the daytime effects. "Pilots cared about contrails a lot," says Rob MacKenzie, formerly of Lancaster University, and now at the University of Birmingham, UK. "Aircraft were tracked using contrails and shot down. So pilots would report them." Using operational records from the US Army Air Force and the British Royal Air Force, and archived weather data, Timmis and MacKenzie realised they could compare temperatures immediately beneath a raid's flight path to those several kilometres upwind, where there would have been no contrails. Clear May morning Conditions were ideal as one particular raid took off on the morning of 11 May 1944, with clear skies and enough moisture for contrails to form. Timmis and MacKenzie found that where the aircraft circled and assembled into formation it was significantly cloudier and 0.8 °C cooler than the area upwind of the bases. "It's innovative to use these historical records," says David Lee of Manchester Metropolitan University, UK. He says the documented cooling due to daytime contrails is "entirely consistent" with what is already known. Field studies of contrails are rare, says David Travis of the University of Wisconsin-Whitewater. Most of our understanding of their effects is based on model studies. Travis says studies like this MacKenzie's study could help change that. He previously found that temperatures were more variable when planes were grounded in the aftermath of 9/11, but faced criticism because the contrail effect couldn't be separated from natural variability in the weather. By comparing temperatures on the same day, but some kilometres apart, the bomber raid study was able to get around this problem. Abstract Dense and persistent condensation trails or contrails were produced by daytime US Army Air Force (USAAF) bombing raids, flown from England to Europe during World War II (WW2). These raids occurred in years when civilian air travel was rare, giving a predominantly contrail-free background sky, in a period when there were more meteorological observations taken across England than at any time before or since. The aircraft involved in the raids entered formation at contrail-forming altitudes (generally over 16 000 ft, approximately 5 km) over a relatively small part of southeast England before flying on to their target. This formation strategy provides us a unique opportunity to carry out multiple observation-based comparisons of adjacent, same day, well-defined overflown and non-over-flown regions. We compile evidence from archived meteorological data, such as Met Office daily weather reports and individual station meteorological registers, together with historical aviation information from USAAF and Royal Air Force (RAF) tactical mission reports. We highlight a number of potential dates for study and demonstrate, for one of these days, a marked difference in the amount of high cloud cover, and a statistically significant (0.8 °C) difference in the 07:00–13:00 UTC temperature range when comparing data from highly overflown stations to those upwind of the flight path on the same day. Although one event cannot provide firm conclusions regarding the effect of contrails on climate, this study demonstrates that the wealth of observational data associated with WW2 bombing missions allows detailed investigation of meteorological perturbations because of aviation-induced cloudiness. Copyright © 2011 Royal Meteorological Society -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
