TORNADOES wreak devastation but are very difficult to predict. On one day in
May last year, 50 tornadoes touched down in Kansas and Oklahoma, killing 40
people and causing $1.2 billion of property damage. But according to NASA
researchers, counting the lightning flashes in storms could give meteorologists
a quick and accurate way to forecast when tornadoes will hit.
Steve Goodman of NASA’s Global Hydrology and Climate Center in Huntsville,
Alabama, and colleagues discovered that the number of lightning strikes in a
storm increases tenfold about 20 minutes before a tornado forms, and then falls
off dramatically. “This could help improve the lead time of some tornado
identifications, and also reduce the false alarms,” Goodman told a symposium
last week convened in Oklahoma City to examine the shattering events of last
year.
During part of those storms last May, a NASA satellite carrying an instrument
called the Lightning Imaging Sensor flew over the area, taking snapshots of six
different storms, including some images of tornadoes as they formed. The images
confirmed ground-based observations from Florida which showed that lightning
flashes increase dramatically —from about 10 per minute to 60 or 100 per
minute—as air rises in big updraughts during the preliminary formation of
the tornado. The number of flashes then falls again when air begins to flow in
downdraughts, about 10 minutes before the tornado finally takes shape.
Advertisement
Goodman says he’s not sure yet how well the lightning flashes would predict
tornadoes. But he thinks they might improve the accuracy of forecasts, and hopes
to get NASA’s approval to put a $15 million sensor on a geosynchronous
satellite that could observe most of North America. At the moment, the average
warning time in the US before a tornado hits is about 12 minutes. But many
people are complacent about the warnings, as only 30 per cent of the alerts
result in actual tornadoes.