New Mexico Tech
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Sprite Research
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
What are Elves?
Elves are diffuse regions of luminosity which occur high
above energetic CG discharges of positive or negative polarity. Elves most likely result when an energetic
electromagnetic pulse (EMP) propagates into the ionosphere. Though they
can be accompanied by sprites, the causative mechanism is of an entirely different nature.
Incidentally, elves got their unusual name as an acronym for Emission of Light and VLF perturbations due to EMP Sources. To learn more about elves, check out the following web site: Stanford's Fly's Eye Experiment
Observations
The following is a list of some observations that New Mexico Tech researchers have made in the past couple of years:
Detection of substantial slow field changes produced by some sprites. These field changes are very strongly correlated with the light output of the sprites.
Detailed images of relatively close sprites (within 200 km) which shows the streamer nature of many sprites as well as the occurrence of sprite-jets in the "decaying phase" of some sprites.
Radar documentation of relatively small storms which produced sprites.
3D maps and static electric-field change measurements of lightning which was directly associated with sprites caught on video.
Detection of a significant number of elves caused by negative CGs (in collaboration with Chris Barrington-Leigh of Stanford).
High-speed video of sprites and elves at frame rates as high as 4,000 per second
This web page has been accessed
times since December 18, 1997
Questions, comments, and/or suggestions? Send them to: stanley@kestrel.nmt.edu
This web page was last modified on February 7, 1998 by Mark Stanley