The Hidden Life of Thunderstorms

Scientists are sending unmanned aircraft into electrical storms to learn more about the mysterious inner workings of thunderstorms.

There's much more to a thunderstorm than meets the eye. Literally. If you could see the invisible force fields around magnets and clothes that have "static cling," a storm on the horizon would look very different.

Engulfing and dwarfing the storm clouds, ghostly ribbons of huge magnetic and electric fields would arch high above the thunder clouds to the top of the atmosphere, and would sprawl downward from the clouds like tendrils groping the landscape. These invisible fields are always in motion, swelling and contorting as the storm clouds churn, lurching suddenly as lightning bolts strike.

Scientists have long assumed that this mostly hidden side of thunderstorms serves as the electrical "pump" that maintains a huge difference in charge between the earth's surface and an upper layer of the atmosphere called the ionosphere. There's a voltage drop between the two, measuring somewhere between 150,000 and 600,000 volts. Left to itself, this difference should naturally balance out in about 15 minutes, but it doesn't.

So a pump must exist. Unfortunately, the numbers don't add up. Scientists are still trying to figure it out: All the cloud-to-ground lightning strikes occurring over the whole planet - about 15 strikes per second - don't move enough electric current to maintain the charge difference seen. Something else must be happening.

Image courtesy The Aerospace Corporation Thunderstorms are also huge electrical dynamos.

"There are other sources besides lightning, and that's part of what we're trying to get a handle on," says Richard Blakeslee, a scientist at the Global Hydrology and Climate Centre at NASA's Marshall Space Flight Centre

He explains: "The earth and its atmosphere are like a giant electric circuit. In fair weather, the charge difference between the ionosphere and the ground drives a steady trickle of current from the atmosphere to the ground, despite the fact that air is a poor conductor of electricity."

Image courtesy NASA Earth's surface and the ionosphere form an electrical circuit. Thunderstorms help keep the current flowing.

"So something must drive a current back from the earth up into the atmosphere to complete the loop and keep the circuit flowing - namely thunderstorms. The two flows should be equal, but so far we still haven't 'balanced the budget'."