Scientists Discover Origins of Jellyfish-like Sprites in the Atmosphere: Plasma Disturbances

Atmospheric sprites have been known to exist for nearly a century. Yet exactly how they formed and where they come from have been a mystery--until now. Scientists have now discovered how sprites form.

Sprites are optical phenomena that occur above thunderstorms in the D region of the ionosphere. This area of the atmosphere is located just above the dense lower atmosphere, about 37 to 56 miles above the Earth. The ionosphere in particular is important because it facilitates long distance radio communication.

While sprites appear above thunderstorms, though, not all thunderstorms produce sprites. Instead, recent modeling studies reveal that plasma irregularities in the ionosphere are a necessary condition for the initiation of sprite streamers.

So what exactly do sprites look like? They look a bit like a fiery orange jellyfish with bluish filamentary tendrils hanging down below. In videos, you can see that the downward hanging filaments form much more rapidly than the horizontal spread; this in particular led the scientists to suggest that localized plasma irregularities cause the streamers to propagate.

The the researchers used a two-dimensional cylindrical symmetric plasma fluid model, a mathematical model of the ionization movements in the sprite, in order to study sprites a bit more closely. They used this model to recreate optical sprite creation, and were able to determine where the sprite streamers originated in addition to estimating the size of the plasma irregularity.

After further examination, the researchers found some potential causes for these plasma irregularities. The most obvious is the existence in that area of a previous sprite. Another cause could be meteor events.

The findings reveal a bit more about atmospheric sprites. By using high speed videos and fluid models, the researchers have shown how these phenomena form. This, in particular, is important for understanding how these phenomena influence radio communications.

The findings are published in the journal Nature Communications.