Upper Atmosphere Lightning

Note: The education section is still under construction and not yet finalized.

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.

Pasko ESOp

Blue Jets and Gigantic Jets are extension of cloud flashes in which one end of the bidirectional leader network propagates upward beyond the thunderstorm.  Sprites, Sprite Halos and Elves initiate and develop spatially separate from the thunderstorm in response to the electric field change caused by a lightning flash in the underlying storm.

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 and therefore only excited N2 in a band that emits blue light.

flashes blue jet

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.  More digital still images have emerged of Gigantic Jets and typically a defined luminous leader is visible from the storm top with more diffuse blue emissions below 50 km and red emissions above 50 km. Due to the red diffuse emissions above 50 km, many people mistake images of Gigantic Jets as red Sprites.  They are two different phenomenon with Sprites being spatial separate from a thunderstorm.

flashes gigantic jet

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.