Over The Horizon

Sprites on Tape

A strange atmospheric phenomenon, known as "red sprites", has been captured on video by a research team from the University of Otago, working 60 kilometres from Darwin, Australia. The 72 images mark the first time the red sprites have been videoed outside the US or from the Space Shuttle -- and is regarded in science circles as a remarkable achievement.

Red sprites are believed to be produced by an electrical discharge from the top of a thunder cloud (about 10 km in altitude) to the base of the ionosphere (90 km up). The jellyfish-shaped luminosity usually extends between the 50-80 km range and is generally about 50 km wide. The dozen or so "jellyfish tentacles" which hang down are only about one kilometre in diameter.

The existence of red sprites was discovered only a few years ago and by accident, when a very sensitive video camera was under test in the US. Until now, the only ground-based video images have been made in the US, mainly in Colorado, though some have been observed from the Space Shuttle.

The Otago team, led by Professor Richard Dowden, had previously established a link between very long wavelength (15 km) radio echoes and red sprites in Colorado and deduced that such radio echoes recorded in the Darwin area during the last 1996/97 wet season meant that luminous red sprites must occur above the Northern Territory also.

Although this is the first video-imaged sighting of red sprites from the ground outside the US, such a phenomenon must have occurred above the Northern Territory every wet season for millions of years. They rarely last more than a tenth of a second and are generally faint, but some -- certainly one and possibly up to nine of the 72 filmed by the Otago team -- can be seen by the naked eye if one is well away from city lights and looking in the right direction.