New Mexico Tech
In the time span of only a few years since their "discovery", sprites have become one of the most hotly researched phenomena in upper atmospheric physics. The characteristics of sprites have been documented by researchers from different parts of the world. However, in spite of the attention that sprites have received, no theory yet exists which satisfactorily explains their initiation and development.
What are Sprites?
Sprites are most likely a form of lightning discharge which develops at high altitudes (30-95 km) in a substantial quasi-electrostatic field originating from a large parent discharge in the cloud below. Predominantly red in color, they usually last no more than a few milliseconds and do not appear to contact the cloud directly. Because of their low surface brightness, they have only been imaged at night (primarily with highly sensitive monochromatic cameras). However, if ones eyes are sufficiently dark-adapted, one can actually detect them without any visual aid.
Most sprites appear to be associated with positive cloud-to-ground (CG) lightning strokes which are significantly displaced from the electrically active cores of thunderstorms. No sprite has yet been found which was initiated by a negative CG (the normal polarity for a CG). However, there are some sprites which are delayed significantly (by over 150 milliseconds) from the occurrence of a positive CG and there may even be some which are not directly associated with a CG at all (though the evidence for this is far from conclusive).
A magazine article on sprites can be found in the August '97 issue of Scientific American