[BAA-ebulletin 00754] RARE SPRITES CAPTURED ON VIDEO

[Rick]

[BAA-ebulletin 00754] RARE SPRITES CAPTURED ON VIDEO
(c) 2013 British Astronomical Association    http://www.britastro.org/

RARE SPRITES CAPTURED ON VIDEO

On Tuesday 23rd July 2013, cameras of the NEMETODE meteor detection network operated by members of the BAA Meteor Section captured a number of sprites, elusive phenomena associated with lightning events that are very rarely observed within the UK. This is a first for NEMETODE, a network of video cameras designed to determine the orbits of meteoroids.

As William Stewart, the camera operator, explained, "Most people are familiar with the commonly observed lightning discharges from cumulonimbus thunderstorm clouds. These clouds typically have an altitude of over 5 kilometres, and we've all seen lightning as it jumps between clouds or between the clouds and the ground. Sprites are very different. They are unusually shaped electrical discharges in the very high atmosphere, almost at the edge of space, at altitudes of 50 - 90 kilometres. They occur above thunderstorm clouds and are triggered by the more commonly observed lightning discharges. Imaging them requires specialist equipment and a significant degree of luck, one of the reasons why their existence has only been confirmed in the past 25 years".

The first event was captured from Ravensmoor, Cheshire at 02:06:16 GMT, early on 23rd July, using a Watec 902H camera with a Computar 8mm f0.8 lens linked to a PC running motion capture software. The progenitor lightning event was determined to be most likely linked with a major thunderstorm that was over Nottinghamshire at the time.

Late in the evening of the same day, a further three events were captured at 22:38:52, 22:42:06 and 22:45:23 (all times GMT). The thunderclouds were however much further away from the camera, most likely over the Humber Estuary on the North Sea coast, and only the tops of the sprites were captured, the lower sections being below the camera's field of view. Detailed image analysis, combined with knowledge of the location of the progenitor events, again confirmed the huge scale and extreme altitude of these rare phenomena. The 22:38:52 event is of particular note as it was simultaneously imaged by a camera of the UKMON meteor detection network and has been the subject of recent publicity.

William Stewart continues, "This was very much a case or right place, right time, right equipment. NEMETODE cameras monitor the same volume of atmosphere from separate locations. The systems are fully automated and, while the operators' sleep, they record moving objects within the cameras' fields of view. When a meteor passes through this volume, its true path (and hence the original orbit of the parent meteoroid) can be inferred through the use of triangulation. Although the system regularly captures meteors, sprites are, in comparison, extremely rare and it was a tremendous surprise to see the first one come up on screen during an analysis later that day. The additional three were a further unexpected bonus. Unfortunately my NEMETODE observing partner, Alex Pratt, was clouded out from his location in Leeds and so was unable to image the events".

Robert Cobain, who participates in a similar network with Armagh Observatory, imaged a possible sprite from his home in Bangor, Co Down in January 2005 while, more recently, Graham Roche recorded sprites from south Dublin in October 2011. The Armagh Observatory has also reported sprite observations associated with thunderstorm activity on the night of the 24/25th July 2013.

Videos and higher resolution images of the NEMETODE sprites, together with links to the other sprites mentioned here, are available at: http://www.nemetode.org/sprites.htm

This e-bulletin issued by:

William Stewart
NEMETODE video camera network

Dr John Mason
BAA Press and Publicity Officer

2013 August 1