For more than 80 years, it has been suggested that an electrical discharge connects the tops of thunderclouds and the lower ionosphere.

Now, due to research conducted during a thunderstorm in Puerto Rico by Penn State scientists, this suggestion is a fact.

There are two types of optical flashes that have been observed over thunderclouds, which are called a sprite and a blue jet, said Victor Pasko, associate professor of electrical engineering.

A sprite forms at the ionosphere, which is a conducting shell around the earth, and shoots downwards at incredible speeds.

A blue jet, on the other hand, charges up from the tops of thunderclouds at extraordinary speeds and is cone-shaped, Pasko said.

"Sprites last for only a few milliseconds, whereas blue jets last hundreds of milliseconds and are easier to see," Pasko said.

Last August and September, an observational campaign was set up at the Arecibo Observatory in Puerto Rico to study lightning and lightning-induced ionospheric effects.

The study that was conducted by Pasko, John D. Mathews, professor of electrical engineering and researchers from Stanford University and New Mexico Tech, was sponsored by the National Science Foundation.

On Sept. 15, during the observational campaign, the researchers used a low light intensifier, which was provided by ITT Night Vision Industries, to video record phenomena during a thunderstorm at night.

The researchers recorded and observed through the naked eye a blue jet that generated up from a thundercloud, which also exhibited features observed in sprites, and reached an altitude of 70 kilometers.

"We saw the blue jet from about 200 kilometers away and even from that distance it looked spectacular," Pasko said. "It was deep blue in color."

Before this observation, it was thought that blue jets only reached an altitude of about 42 kilometers, and that they never made a connection with the lower ionosphere.

The researchers' results show the first video observation of blue jet phenomena from the ground, Pasko said.

Although the phenomena they observed contained behaviors detected in sprites, the researchers classify the it as a blue jet, according to their paper, titled "Electrical Discharge from a Thundercloud Top to the Lower Ionosphere."

The paper was published in the March 14 issue of Nature magazine.

"The initial stage of the observed phenomena closely resembles the general geometrical shapes and propagation speeds of previously documented blue jets, and the event was seen visually to be blue in color," the report states. "We therefore speculate that it can be classified as a blue jet, which propagated upwards beyond the previously documented altitude."

Jeremy George (undergraduate-electrical engineering) helped Pasko in modeling the formation of this newly observed phenomenon.

"I worked with Pasko in developing a two and three-dimensional fractal model to replicate a blue jet," George said.

George is working with Pasko on a paper that will present results of the model, which allows blue jets to propagate up to the altitude of 70 kilometers.

"Our model shows that this can actually occur," George said.