Transient Luminous Events (TLEs) are electrical discharges that occur in the upper atmosphere. Their blue and red colors arise from electron impact excitation of N2 and O2, with blue emission below 50 km and red above 50 km.
Blue Jets and Gigantic Jets are extension of cloud flashes in which one end of the bidirectional leader network propagates upward beyond the thunderstorm.
The Blue Jet is an extension of the positive end of the leader upward after developing between the upper main positive charge region and a negative screening layer as shown below. Blue Jets do not extend further than 50 km in altitude.
The Gigantic Jet is more energetic as it involves the two main charge regions. It is believed that turbulent mixing in the upper part of the storm prevents a discrete screening layer from forming, and therefore, the negative end of the leader network extends beyond the upper positive charge region and into the upper atmosphere. Gigantic Jets have been observed up to 70 km.
Sprites and Sprite Halos are electrical ionization of the air due to the large electric field change caused by cloud-to-ground flashes in underlying thunderstorms. Unlike Jets which are extensions of flashes from a thunderstorm. The remaining TLEs develop spatially separate from a thunderstorm.
A Sprite is the bidirectional breakdown of the rarified air at approximately 60 km. Sprites are typically triggered by an underlying horizontally extensive +CG flash that transfers a large amount of charge to ground. Since negative charge is raised during a +CG flash, the positive end of a Sprites bidirectional development travels downward to altitudes near 20 km, whereas the negative breakdown travels upward to 90-100 km.
A Sprite Halos is a faint short duration expanding illumination at the typical initial breakdown altitude of a Sprite, but fails to develop tendrils (leaders) like a Sprite. Therefore, a Sprite Halo can be thought of as a failed Sprite. Halos are more common than Sprites as lower energy ground flashes can initiate the illumination, but not achieve the charge transfer to cause the development of a Sprite.
ELVES (Emission of Light and VLF perturbations due to EMP Sources) are an expanding ring of light omission at the bottom of the ionosphere. They only last a tenth of a millisecond and can expand to a diameter of 1,000 km.