Red sprites and blue jets are strange lights that appear in the upper atmosphere above thunderstorms.

The red sprites are large flashes of red light that last just a few thousandths of a second. They can reach as high as the lower edge of the stratosphere, about 90 km high.

They are faint and usually require a low light level camera to detect them.

They can spread over huge regions of the sky. Some as large as 10,000 cubic kilometres have been reported.

Over in the blink of an eye

Blue jets seem to emerge directly from the tops of clouds and shoot upwards in narrow cones through the stratosphere at speeds of about 100 km a second.

For two weeks a Gulfstream 2 jet aircraft has carried 8 TV imaging systems above the western United States in search of thunderstorms and sprites.

Observations in the air were co-ordinated with ground based observatories.

One remarkable event was seen over central Iowa. A sprite was seen with tendrils of light trailing all the way down to the clouds.

These dancing lights are undeniably beautiful but scientists would like to know how they are caused.

The sprites and jets indicate that thunderstorms are more complicated than was once thought. Scientists are speculating that they might be an essential part of the earth's global electrical activity.