Fire tornado: how bushfires create their own weather

ten years ago our nation's capital was ravaged by one of the country's worst fires four lives were lost and over 500 homes but the extent of the devastation caused by the Canberra fires baffled scientists and emergency services it was a pretty big shock because I mean there's there's nothing really in the literature which suggests the fire should spread that fast or could spread that fast in the aftermath it was clear that the worst damage was due to something much more savage than ordinary fire storm there was a police car that was a picked off the ground and dumped into a storm water drain there was a series of streets in the southern edge of Chapman which had suffered severe wind damage as well as fire damage and that was difficult to explain what hit Canberra had never before been documented in science Oh a fire tornado On January the 8th 2003 a huge dry lightning storm struck in multiple places across the AC T sparking a large number of fires one of the biggest began here in the Brindavan arrangers but for days fire conditions weren't particularly alarming a very orderly fire behavior very orderly progression across the landscape then on the 18th of January the situation turned catastrophic dry westerly winds came into play temperatures reached 37 degrees causing surface air to mix with the upper atmosphere creating strong gusts so the fire started over there in the valley it steadily moved along that Ridge until it got to a point into fresh fuel and his whole area was ignited within about 20 minutes this whole area this little area was alive at that stage it was perhaps the biggest fire event that this area had seen for quite a long time Stephon Wilkes was in a chopper at 2:00 p.m. that day mapping the fire I was trying very hard to find out where the front of the fire was to give us an idea of how fast it was coming into town and there was no front the fire had broken up into thousands of smaller fires we were seeing things that none of us had ever seen knowing things were wrong but not being able to make any sense of it suddenly it all went quiet and the chopper pilot turned to me and said Steven I think we're going to get out of here and I looked around and I realized it if I panicked at all I was probably dead as we left I took a photograph of what I saw was a slight rotation and some light coming through the plume and we believe that was pretty close prior to the tornado for me to be honest with you I've only recently realized how lucky I was the next day Stephen returned to document the damage we were speechless we're devastated the houses that were alight and wind damage that was done there were massive trees fully mature yellowbox trees just torn up out of the ground moved a few meters and dumped what kept coming to my mind was a tornado in a science literature fire tornadoes didn't exist but as researchers slowly pieced together information from aerial and ground surveys no other explanation fit this is the damaged path that was mapped from the air soon after the event and it shows it extending from around Mount kori through to the suburb of camber that looks like a quite a long path it extends a total of 25 kilometers was just under half a kilometre in widths before it hit the city whatever ripped through the suburb of Chapman hit the Pierce pine plantation first amidst the blackened trunks it left a distinctive trail of destruction the trees had all been snapped off at about three metres above the ground the alignment of the trees left lying on the ground was indicative of a vortex softwood trees like Pines can only snap off when wind speeds reach a level equivalent to two on the Fujita scale of tornado intensity the highest being five at this strength trees can be uprooted cars lifted off the ground and roofs torn off all of this supported our claim that the wind speeds were around 250 km/h but ironically the real clincher was areas where there was no damage at all the key part of it is the fact that these gaps are in here a tornado is able to lift off from the ground and reattach later and these gaps support the notion that it is a tornado the alternate hypothesis a fire whirl is unable to lift off from the ground that's attached to the hot fire ground as the evidence came together extraordinary images emerged of the tornado itself helping to define the characteristics of the vortex tornado in the photo corresponds to about two centimeters so that means that the base of the tornado must have been about half a kilometer wide they're perfect war meter that's amazing it's 4:00 p.m. in can bar district playing fields very different-looking afternoon - when Tom Bates stood here watching the fire war over the hill so where did you first see the tornado coming on male arrowing he attacked across the top of the hill spot fires loving the bottom yeah stood up on this side as it was just like a great big wave ready to burst incredibly Tom caught the moment on film oh never a more loss anything like it Oh at the far right the funnel of the tornado comes into view this is Rafael sitting in a i-10 shootin team over here I didn't in camera Illinois killing me no one has captured a tornado like that as clearly in a fire situation before one of the interesting things about the video was a pair of football goal posts in the foreground that gave us a measurement stick in the vertical direction so we could go out to where the video was taken and we could measure the speed of movement over the ground and also the wind speeds within the vortex we were able to estimate a vertical wind speed of over 150 corn meters per hour scientifically documenting a fire tornado was a world first but that left a vital and more important research question how could a series of relatively contained fires develop so quickly into such a violent pyro convective event I guess I was really interested in trying to understand what caused the thunderstorm which spawned the tornado in the multispectral line scans taken on the day dr. Jason Sharples was struck with the same puzzling images again and again sections of the fire spreading sideways these are instances where the fire where it would normally be spreading downwind have started actually spreading a crosswind and what we found were that these instances without exception were connected with Lee facing slopes I want to leave facing slope facing away from hot westerly winds normally these are considered the sheltered sides the safest areas to take cover from a fire but in the case of the Canberra fires it was these slopes that burnt the fastest and the most intensely framed a hypothesis that this this phenomenon was being caused by the interaction between the fire that went in the terrain so what we did in Portugal was to try and emulate these conditions in a combustion tunnel in the experiments the fire behaved exactly as it did in Canberra racing up the Li slope and channeling sideways as it hit the headwind multipled spot fires were created igniting large tracts of the slope before these experiments confirmed it no one knew a fire could behave in this way here's what's going on the wind travels upslope but as it hits the crest it's moving too fast to follow the terrain and lifts off swirling back on itself in an eddy the fire moves with it and the disastrous result is that two sides of the hill light up at the same time with extraordinary speed turns a small fire in we're very big fire very quickly rather than spread in a as a fire front as it normally would it causes what we call deep flaming so that's where we get large tracts of the landscape all igniting in a relatively short amount of time the intense and deep flaming caused by the fire channeling events happened immediately before the thunderstorm formed with such a huge area alight a massive amount of energy was released into the atmosphere in fact in the peak ten minutes of flaming more energy was released than the Hiroshima atomic bomb the massive smoke plume of heat and moisture formed a gigantic pyro cumulonimbus cloud a huge supercell thunderstorm Stephen took these incredible photographs as it formed as the moist hot fire plume is lifted into the upper atmosphere it's hit by upper-level winds of a different speed and direction setting up a vortex and a tornado is born as for fire tornadoes the team hopes never to see another one but they're even more hopeful that their discoveries on fire behavior may one day save lives when it comes to an extreme fire we have learned an awful lot about how to stay safe and how to protect the community the real challenge now is getting those learnings out right across the bush fire industry you

Channel: ABC Science

Views: 560,221

Keywords: Bushfires, Fire tornado, Australian bushfires, Australia, Canberra, Fire, bushfire, Fire Whirl, catalyst, abc science, australian science, abc, abc tv, abc iview, research, education, science education, lightning, storm, tornado, cyclone, twister, whirlwind, el tornado, the storm, thunderstorm, canberra bushfires 2003, canberra bushfire footage, crazy weather, combustion, bushfire australia, Anja Taylor

Id: rqYEeivt8Eg

Length: 11min 9sec (669 seconds)

Published: Fri Jun 07 2013