Deep in the tropical jungle of Puerto Rico lies the NSF's Arecibo Observatory, where for the first time a team of researchers has captured video evidence from the ground of a lightning phenomenon known as a blue jet. The discovery is the first ground-based evidence linking the ionosphere with cloud tops in blue jet events.

According to Victor Pasko of Penn State, an electrical engineer working at Arecibo, "Pilots and others reported observations of red sprites and blue jets long before the first one was captured on video, and numerous undocumented reports of similar phenomena have appeared in scientific literature for over a century."

Blue jets develop at cloud tops at 12 to about 26 miles. They appear blue to the naked eye, last for up to several hundreds of milliseconds and are cone-shaped.

According to Sunanda Basu, program director in NSF's atmospheric sciences division, which funded the research, the video is the first ground-based evidence of a direct electrical discharge from a thundercloud top to the lower edge of Earth's ionosphere. The electrical contact may represent an important component of the global electrical circuit, says Basu.

The event was recorded using a monochrome low-light video system, but the researchers all agree that the phenomena was seen visually as blue in color. The top of the jet appears to look much more like a red sprite than a blue jet, with hot spots and a fuzzy diffused appearance. Scientists do not yet know if this is a new phenomenon.

[Cheryl Dybas]
-NSF-