Red SpriteCredit: NASA

Out of the cold blue sky came the sprite, jets, and elves.  Kind of sounds like the first line of a philosopher's poem from antiquity.  Maybe a more catchy title would be "Sprites, Jets, and Elves - Oh My!"  However, the title of this article does not refer to mischievious fairies or benevolent woodland dwelling creatures of myth, but to three unique phenomena of the upper atmosphere.  We're all aware of lightning, a huge electrical discharge in the atmosphere during a thunderstorm.  But what you might not know is that scientists don't really understand lightning in general.  And electrical activity can delve into the very strange the higher up in the atmosphere you go. 

A Little Info on Lightning

In a thunderstorm, through a process that is not understood, charges separate and aggregate.   The ground beneath the thunderstorm becomes oppositely charged to the base of the clouds, thus creating an electric field between the storm clouds and the ground.  Lightning discharges occur when the resistance between the charged particles in released in the form of energy.  The lightning strike process is way too complex for this article, but it will be mentioned that lightning strikes are either cloud discharges, or cloud-to-ground.   Cloud-to-ground strikes are for obvious reasons much more dangerous to humans.  Lightning is by itself very strange, and we would most likely find it so, if it wasn't so common.  However, as scientists are beginning to discover, there are quite a few phenomenons associated with electrical fields in the open atmosphere, and they are all strange and complex. 

 

 

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Red Sprites

Upper-atmospheric lightning is a term used to describe a family of electrical phenomena in the upper-atmosphere.  Scientists prefer the term transient luminous event (TLE), as the phenomena is distinctly different from lightning, and lacks several characteristics of tropospheric lightning.  Sprites are the most common TLE.  A sprite is a bright flash of red light occurring above a thunderstorm.  The general form of a sprite is large, red tendrils stretching up into space.  Often times sprites are accompanied by a halo, simply called a sprite halo. 

Sprite from the International Space StationCredit: NASA

Sprites had been reported for more than a hundred years back, but were not scientifically proven until 1989 when they were accidentally caught on film.  Other types of sprites include the jellyfish sprite, which branches out over an area of about 30 miles, and the C-sprite which resembles a column.  Sprites appear to be related to lightning activity within the thunderstorm it is associated with.  Sprites usually only last a couple of milliseconds, but they have been known to last up to two seconds. 

 

Blue Jets

Blue jets project from the top of a thunderstorm cloud into the sky above in a narrow cone.  They are blue in color and are brighter than sprites.  Unlike sprites, they do not appear to be closely related to lightning.  Jets normally last under a second and reach up to about thirty miles from their origin.  Sometimes a blue luminous phenomenon is recorded above thunderstorms that resemble blue jets, but are not in a cone shape.  It is thought that these are blue jets that don't quite materialize, and are tentatively called blue starters.  A couple of jets have been observed to reach 60 miles above the associated thunderstorm. 

Blue JetCredit: pbs.org

Blue jets were unknown to science and discovered only in 1994 by accident.  There are to this day less than a hundred photographs of blue jets. 

Elves

Sprites with ELVESCredit: NASA

ELVES are a flattened, dim glow about 250 miles in diameter.  They occur about 60 miles above the surface directly over thunderstorms.  ELVES were first discovered during a shuttle mission in 1990.  Their color for a while was a mystery, but has since been determined to be a dim red hue.  ELVES is an acronym for Emissions of Light and Very low Frequency Perturbations due to Electromagnetic Pulse Sources which describes the process that creates the light that is generated.