Deadliest Tornado Outbreak in Decades Was Fueled by Smoke From Land Clearing

Even experienced weather forecasters were taken aback by the ferocity of the 2011 tornado outbreak. On its worst day, April 27, more than 120 twisters touched down in the Southeast, doing $4.2 billion of damage and killing 316 people.

Now a computer simulation of the day's events suggests that smoke drifting into the United States from fires set to clear farmland in Central America helped intensify the fatal wind funnels. Researchers publishing the finding in an upcoming Geophysical Research Letters hope that meteorologists will begin to consider air pollution a risk factor when making tornado forecasts.

"I never expected to see an April like that," says Greg Carbin, a meteorologist at the the National Oceanic and Atmospheric Administration (NOAA) Storm Prediction Center in Norman, Oklahoma, who wasn't involved in the research. "Everything came together to produce an outbreak the likes of which hadn't been seen for nearly 40 years."

Tornadoes from May 1950 to May 2013, rated 1 to 5 on the Enhanced Fujita (EF) scale. Twisters frequently strike in the Deep South as well as in the Great Plains. The EF scale is based on wind speed and degree of damage.

MARTIN GAMACHE AND VITO ZARKOVIC, NG STAFF; CRAIG HOWARTH, 422 SOUTH. SOURCES: NOAA, TWISTEX

Smoke and other tiny airborne particles called aerosols have been linked to severe weather events before. Aerosols may quiet tropical storms and ramp up the amount of lightning dished out by thunderstorms, for instance. One study blamed human-made haze for an uptick in summer tornadoes and hailstorms, which are more common on weekdays along with exhaust-belching traffic.

Still, you won't hear about aerosols in local news coverage of storms; the science remains controversial. "There's a lot of debate in this area," says David Lerach, an atmospheric scientist at the University of North Colorado, in Greeley. "Some people think that the effects of aerosols on storms are insignificant, while others have staked their careers on it."

Even global climate change simulations struggle with aerosols, which along with clouds remain the single greatest source of uncertainty in those models.

Making a Bad Situation Worse

To pin down smoke's influence on tornadoes, Pablo Saide, an atmospheric scientist at the University of Iowa, in Iowa City, and his colleagues first turned to NASA's Aqua satellite. Its payload includes an infrared camera that in 2011 detected the heat of fires in Central America. Such fires are set every year, before the summer monsoons, to clear land for farming.

Link:
Deadliest Tornado Outbreak in Decades Was Fueled by Smoke From Land Clearing