Lightning: Red Sprites in Atmosphere, Explained
Lightning sprites are bright flashes in the atmosphere that happen 25 to 50 miles above thunderstorms, and they often resemble red jellyfish. They've been seen by airline pilots and have appeared on NASA shuttle videos.
Now a study from Florida Institute of Technology, led by professor Ningyu Liu and published in a recent issue of Nature Communications, provides evidence that atmospheric gravity waves create sprites.
Why should we study these mysterious flashes in the sky high above thunderstorms? Sprites can interfere with or disrupt long-range communication signals by changing the electrical properties of the lower ionosphere, so it is important to understand how they form in our atmosphere.
The researchers' work included computer-simulation results from a sprite initiation model, and dramatic images of a sprite event. The study found that perturbations in the upper atmosphere created by atmospheric gravity waves can grow in the electric field lightning produces, and eventually lead to sprites, according to a release.
"Perturbations with small size and large amplitude are best for initiating sprites," Liu said in a release. "If the size of the perturbation is too large, sprite initiation is impossible; if the magnitude of the perturbation is small, it requires a relatively long time for sprites to be initiated."
Part of the work included analyzing a sprite event captured simultaneously by high-speed, high-sensitivity cameras on two aircraft during a mission sponsored by the Japanese broadcasting corporation NHK. High-speed images show that a fairly long-lasting sprite halo occurred before the fast initiation of sprite elements, just as the model predicted, according to the release.
Liu added, in a release, "Our findings also suggest that small, dim glows in the upper atmosphere may be frequently caused by intense lightning but elude the detection. There may be many interesting phenomena waiting for discovery with more sensitive imaging systems."
Collaborators from Florida Tech (one of whom is now at University of New Hampshire), University of Alaska Fairbanks, and the United States Air Force Academy worked on the study.
Did you know? As with tornadoes and other phenomena, some people "hunt" lightning sprites as part of their job--like the team from University of Alaska Fairbanks, the U.S. Air Force Academy, and Fort Lewis College in Durango, Colo., mentioned here.