Mission to Geek

Sprites, jets, and elves don't sound like the stuff of science, but they are. They are the names given to various colored flashes of light seen high in the Earth's atmosphere, flashes of light that until recently scientists believed were figments of the over-active imaginations of airline pilots, who usually were the ones to report them.

It's now most commonly believed that they are, in effect, upwardly-striking lightning from the tops of thunderstorms or the remnants of the "cells" that make them up.

In a simple form, lightning happens when the potential difference between in the charges in a stormcloud and the ground below become great enough to overcome the electrical resistance of the air between. But that surge of charge from cloud to ground can leave in its wake a new potential difference: between the cloud and the ionosphere above it. If and when that potential difference is great enough, a jolt of charge can slam upwards to the ionosphere.

It's all part of a global electrical circuit which is now being studied by satellites.

The phenomena are difficult to study as they occur between 50 and 100km (30-60 miles) above the Earth's surface, too high for most aircraft and too low for satellites.

To study them, the Taiwanese government built the Republic of China Satellite 2 (Rocsat -2), which includes a sensor built by the University of California at Berkeley, US, to gather information about the lights.

The instrument contributed by the Americans is called Isual - the Imager of Sprites and Upper Atmospheric Lightning. ...

The first Isual image was returned on 4 July. It showed red sprites - short fluorescent "tubes" glowing like neon lights - reaching to the ionosphere.

Another image showed a brilliant lightning flash with a trio of red sprites above it and a sprite halo encircling it. ...

The red sprites are formed in the regions of molecular disintegration [caused by strong local electric fields]. The blue jets, however, seem to come from the top of thunderclouds.

Elves are rapid bursts of light due to electromagnetic pulses from lightning jolts.

After (somewhat reluctantly) concluding the earlier reports were based on actual observations, some scientists have suggested that the flashes may also be the source of many of the UFO sightings airline pilots are rumored to have had.