The study of lights in the upper atmosphere pushes the capabilities of science, especially high-speed video. It also takes luck and friends in high places—like mountaintop observatories.
Special viewing sites are needed to see sprites, as they always hide above thunderstorms. At the Yucca Ridge Field Station, run by FMA Research in northern Colorado, sprite-watchers can see lightning from storms 1,000 kilometers away over the Great Plains. A similar observatory is in the Pyrenees range of southern France. Other researchers take storm-jumper planes into the turbulent night skies to capture the elusive flashes.
The other major observing platform is in orbit. Important research has been done from the Space Shuttle, including the fateful flight of Columbia that crashed during reentry in 2003. And Taiwan's second satellite, launched in 2004, is dedicated to this field.
The Role of Luck
The hunt for sprites and their siblings has also depended on lucky breaks. Sprites were first recorded in 1989 when some University of Minnesota scientists, waiting to film a rocket launch, pointed the camera at a distant thunderstorm. One of them checked the wiring and fixed a loose cord. Minutes later the tape caught a flash so brief it occupied only two frames. Those two frames of video launched a whole new branch of Earth science.
On 22 July 2000, Walter Lyons was at Yucca Ridge shooting video of a huge "mesoscale" storm complex when a smaller isolated "supercell" thunderstorm drifted northward, blocking the view. Supercells—the typical anvil-shaped cumulonimbus thunderstorms—do not produce sprites, but Lyons let the cameras roll. To his surprise, the recordings showed two new kinds of lights at the top of the supercell: gnomes and pixies.
Lyons is still looking for new lights. The scientific literature has eyewitness descriptions of lights in the high atmosphere dating back more than a century. Most correspond to sprites and blue jets. But a tantalizing handful describe bright white streaks rising straight and unbranched from thunderstorm tops. A few photos give the further detail that the tops of these lights shade to blue.
Some day we will capture these on tape, analyze their spectra, and give them a name. Like sprites, elves, and trolls, they have always been here, but we never had eyes to see them with.
The Sprite Community
The annual December meetings of the American Geophysical Union have been reunions of the close-knit sprite community since 1994. At the 2001 session, the group in attendance paused to remember their late friend and mentor John Winckler (1917–2001), the geophysicist and collector of odd lightning stories who pointed the camera at that Minnesota thunderstorm in 1989. At the same time, talks by a European-African group and a sprite-hunting team from Taiwan were proof of the field's growth.
Every year brings advances in the study of sprites and their relatives. At the turn of the millennium this is what we were learning:
- David Sentman, the man who gave sprites their name, documented gravity waves in the high atmosphere caused by sprites. In effect, sprites "splash" energy into the ionosphere like a swimmer flopping into a pool. Thus they join meteors, eruptions, thunderstorms and earthquakes as causes of ionospheric gravity waves.
- The STEPS 2000 campaign recorded sprites as other observers detected distinctive infrasound signals—I would call these "sprite thunder." Walter Lyons prepared a PDF document on the subject.
- The first sprites were observed in Brazil, a major thunderstorm playground, using instrumented balloons and planes. See them in this photo gallery.
- Tohoku University's sprite group (apparently defunct as of 2009) looked for sprites in winter, monitoring cold-front storms in the ocean near Japan. This meteorological setting is quite different from the Great Plains of North America, yet sprites appear there too.
- And a group at National Cheng Kung University in Taiwan observes over mainland China as well as the Pacific. They were the ones who discovered gigantic blue jets.
PS: This atmospheric research is also tied to the ongoing study of ordinary lightning. New networks are observing lightning in wonderful detail, yielding data that can give insight into the forces that cause sprites. To anyone who has ever watched heat lightning hidden deep in the high clouds, the resulting pictures are a magical glimpse at something never seen before.