The ancient Greeks might have thought Zeus was furious with heaven itself. The power of lightning strikes that shoot upwards from storm clouds has been measured for the first time 鈥� and they turn out to be every bit as powerful as normal lightning.
First caught on camera in 2003, 鈥済igantic jets鈥� shoot upwards from thunderclouds and can reach altitudes above 80 kilometres. But it wasn鈥檛 until 21 July last year that at Duke University in Durham, North Carolina, and his colleagues managed to measure the electrical discharge from a single gigantic jet, released from .
鈥淣o one had been very close to one with the right radio instrumentation before,鈥� Cummer says. 鈥淪o we didn鈥檛 know whether they just petered out without doing anything much, or whether they actually took some charge and dumped it somewhere.鈥�
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Electric jet
The jet came out of a high storm cloud, beginning at an altitude of about 14 kilometres, and shot upwards for a further 75 kilometres.
At those heights, the atmosphere is a much better electrical conductor than at ground level because of ionising radiation from space. As a result, the jet was able to discharge 144 coulombs of charge into the upper atmosphere in about 1 second.
This is comparable to the charge transferred by a large cloud-to-ground lightning strike.
鈥淚t鈥檚 fantastic that they see such a high charge transfer between the thundercloud and the ionosphere,鈥� says of Pennsylvania State University in University Park.
Changing weather
Gigantic jets could be important for our ability to predict lightning strikes.
鈥淭here is this newly identified path for discharging the thunderstorm, and a lot of charge can be moved,鈥� says Cummer. 鈥淚n storms that can produce gigantic jets, it might influence what other lightning is happening in the storm.鈥�
This time, however, the team found no difference in the rate of ordinary lightning strikes around the time of the gigantic jet. 鈥淚鈥檓 surprised they saw no drop in lightning rates before or after the jet 鈥� but that might be because of the sheer size of the storm,鈥� says Pasko.
Gigantic jets are one of a host of new atmospheric phenomena discovered in recent years. Other examples are sprites and blue jets.
Journal reference: , (in press)
