3st PART

















Above the clouds thunderstorms, gigantic jets of light rise up to the ionosphere sometimes. These flashes of light are called T.L.E. They are hardly visible to the naked eye. But some astronauts from the International Space Station were able to see, when they were just over a violent thunderstorm and at the right time as these events last less than a second.

Click here to see a video of sprites and blue jets ESA 750ko. Credit : Danish National Space Center

- Farfadets or Sprites :

They are bright flashes that occur in the mesosphere, above cumulonimbus is 20 to 96 km altitude over a width of 15 km. This is when the electric field is strong enough and the air tenuous enough, then the electrons will accelerate to the speed required to transport their kinetic energy in the molecules they encounter, what excites and releases this energy in form of light called sprites. They occur only above active thunderstorms and they are mostly associated with positive lightnings so when the lightnings go down towards the ground. They are mainly red and they usually don't last more than a few milliseconds. The first images of a sprite were obtained by chance in 1989. To see them you must be able to see above the thunderstorm and a view on a dark background stellar. Because of their low brightness, the sprites can't be seen in the presence of light, as found in cities. The best distance to see is to be 200-300.km from the thunderstorm. At this distance the sprites are a vertical angular distance of 10-20°.

Halo sprites precede sprites and propagate downward from about 85 to 70 km altitude and last about a millisecond. These halos are thought to be produced by the same physical process that produces sprites, but for which the ionization is too weak to cross the threshold required for streamer formation.

Farfadets or Sprites

Click here to see this animation of
filmed Sprites, gif format : 1 MB

- Elves :

Just after the sprites it can appear the elves, and their duration is more ephemeral, less than a thousandth of a second. They occur above the clouds positive or negative polarity during a lightning. The origin of the elves are powerful lightnings that emit electromagnetic pulses propagating very quickly from lightning. They can be spread on 400 km in diameter. When the upper part of this "sphere" reached an altitude of approximately 75 to 100.km, the electrons will be accelerated by an electric field conveyed by these impulses. The gas molecules will be excited and affected by the electrons such that they will release the surplus energy into light in the form of a ring. This occurs so rapidly that this ring will be seen as a flattened disc. They were discovered in 1994.

Elves layer


- Blue Jets

These optical phenomena were observed for the first time in 1994. They are conical jets of blue light propagating from the top of the electrically active core regions of thunderstorms to the upper atmosphere at a speed of about 74,56 mps (120 km/s) and don't exceed 40 km altitude with a lifetime of a couple of tenths of a second. But they aren't associated with cloud-to-ground lightning. They are also brighter than sprites. Blue jets occur much less frequently than sprites.

Click here to see the animation
of the Blue Jet in format gif : 850ko


- Gigantic Jets

gigantic jets are by far the rarest of TLE that have so far been discovered. The first confirmed gigantic jet was reported in 2001, after American researchers saw a blue jet reaching 70 km above the clouds at the Arecibo Observatory in Puerto Rico.These electrical discharges can take several forms, such as sprites (orange-red flashes) and blue jets, which appear as blue cones.


- Trolls

Trolls, also recently observed, resemble blue jets, but are red and seem to occur after tendrils of vigorous sprites extend downward toward the cloud tops.


- Emission of radio waves, X-rays and gamma

Gamma and X ray bursts of short duration (about 1 millisecond) were detected by the Compton satellite who observed gamma rays from space. These rays occur above the thunderstorms regions and their sources are assumed to be at altitudes of more than 30 km. When sprites are produced by a relativistic electron avalanche triggered by cosmic radiation, electron beam may interact with air molecules and produce X-rays and secondary gamma. Sprites require an energy of about 20 electronvolts. But gamma rays in demand over a million electronvolts.

Violent lightnings emit radio waves into the Van Allen belts which is situated in the magnetosphere which is an extension of the Earth's magnetic field that reaches the outer layers of the atmosphere. Energetic electrons traveling near the speed of light between the two ring-shaped zones, separated by a space known as the region of the slot of the Van Allen Belt, consisting of turbulence. This space is where the aurora borealis creates what could be a safer place for the orbits of satellites.

During solar flares emitted particles decompose instantly and flow around the area of the slot of the Van Allen belt.

The Van Allen belt upper and
lower and between the region
of the slot of the Van Allen belt

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