https://apod.nasa.gov/apod/ap220912.htmlResearch has shown that following a powerful positive cloud-to-ground lightning strike,
red sprites may start as 100-meter balls of ionized air that shoot down from about 80-km high
at 10 percent the speed of light.
The most interesting detail in that statement is the movements towards Earth. I have never heard about that direction regarding phenomena observed above clouds. Usually in articles about sprites, blue jets and related, it's about movement into space, which leads the reader to think about those observations as being results of lightning below and not considering the energy source above.
I did some calculations about that to estimate the energy needed for acceleration of one of those air spheres:
- sphere radius: r=50m
- air density at 80km: d=0.0000157005 kg/m^3 (near ground it is 1.225 kg/m^3)
- speed: v=0.1c=299792000 m/s
- sphere volume: V=4/3pi*r^3
- sphere mass: m=V*d = 523598 m^3 * 0.0000157005 = 8.22 kg
- energy for acceleration: E = 3.6938724981504E15 J = 1026 GWh
- yearly electric energy consumption of Germany: 510 TWh
Difficult to imagine how hot air below clouds could cause this