Red Sprites and Blue Jets

Red sprites and blue jets are optical phenomena that occur above the cloud tops in intense thunderstorms. The following YouTube Video shows red sprites and blue jets in real time, courtesy of The Sprites Campaign conducted by the Geophysical Institute of the University of Alaska Fairbanks. Following the video, I will go into the details about what these are, how they form, and when then form.



RED SPRITES
Red sprites are generally associated with cloud-to-ground or cloud-to-cloud lightning. It is estimated that they begin above the cloud tops and extend up to a 95 kilometer (~60 miles) altitude. The bulk of the red sprites occur in the mesosphere, the 3rd layer of our atmosphere. The sprites are usually red at the top and blue tinted near the bottom tendrils where they shoot up from. So what gives them the red color? Current thinking is that sprites result when free electrons are accelerated by the sudden charge in electric field strength caused by the parent lightning discharge below in the storm. The electrons slam into molecules of nitrogen causing the nitrogen to glow. The massive, dim light flashes usually last about a few thousandths of a second. Research suggests this phenomena occurs nearly simultaneously with positive cloud-to-ground lightning strokes and they typically form in clusters stretching 50 miles or more across the sky. It is believed that they for from the disruption of the atmosphere's electrical field in such a way that charged particles in the upper atmosphere are accelerated downward toward the thunderstorm and upward to higher levels within the atmosphere. It is believed that scientists knew of the phenomena as early at 1886; however, their knowledge was not extensive and they merely reported in their journals to have seen something high above the thunderstorm that they did not understand. It wasn't until 1989 that a professor and his graduate students from the University of Minnesota accidentally captured video of this event while testing a low-light video camera for an upcoming research rocket flight. They received the name 'sprites' after being suggested by Professor David Sentman of the University of Alaska-Fairbanks in 1994. 'Sprites' are mythical, fleeting, and playful creatures that appear in mythology and Shakespeare's plays.

BLUE JETS
Blue jets dart upward in a cone-like shape from the tops of thunderstorms that experience vigorous lightning activity. The narrow cones propagate upward in narrow cones of ~15 degrees full width at vertical speeds of roughly 100 kilometers/s (approximately 50-100 miles per second). The reach a height of about 25-50 miles before they begin to fade out. Unlike red sprites, they do not appear to be correlated to specific cloud-to-ground lightning discharges, and to this day they continue to not be well understood. They are more likely to occur at the highest portion of an intense thunderstorm cell, such as ones that produce tornadoes and severe weather. It is possible to see blue jets with the naked eye because they are brighter than sprites.


Photo Courtesy of http://www.electricyouniverse.com

Sources:
Ahrens, C. Donald. "ELVES in the Atmosphere." Meteorology Today: an Introduction to Weather, Climate, and the Environment. Belmont, CA: Brooks/Cole, CengageLearning, 2009. 390. Print
Heavner, Matt. Red Sprites and Blue Jets. Geophysical Institute of the University of Alaska Fairbanks. Web. 22 Aug. 2010. http://elf.gi.alaska.edu/.
"Lightning." Wikipedia, the Free Encyclopedia. Web. 22 Aug. 2010. http://en.wikipedia.org/wiki/Lightning#Blue_jets.
"Sprites, Blue Jets and Elves." Sky-Fire.tv. Sky-Fire Productions, Inc. Web. 22 Aug. 2010. http://www.sky-fire.tv/index.cgi/spritesbluejetselves.html#19.