A red sprites appearance lasts from ~20 to ~100 milliseconds,
but can be very bright and visible to the naked eye in dark
areas.However, the brightness remains several times below a
lightning discharge. On average, red sprites appear at an altitude
of about 40 - 90 km from the stratosphere (<50km) through the
mesosphere to the thermosphere (>80km). Sightings up to an
altitude of 100 km in the thermosphere are also possible. The
height dimension of a single sprite varies from ~10 km to ~60 km,
the width can possibly reach 5 - 30 km. However, some 'sprite
walls' or 'multiple sprites' can exceed 100km horizontally.
But how does the rare luminous phenomena come to this name, when
they were discovered and what is the reason of origin?
Until 1989, the existence of Red Sprites was generally denied
because only jet pilots announced sporadic sightings. Here they
reaped rather grumpy and sarcastic reactions :-(. Thus, many
sightings have been omitted. 1989 the first Red Sprite photos did
succeed, but due to the not yet advanced camera technology the
results were scientifically useless.
1991 the astronauts of the former Space shuttle mission succeeded
photographically to capture this phenomenon specifically the first
time from space. These photos served as the first meaningful
evidence. Afterwards high-tech peppered research aircrafts were
inserted by very costly experiments from the NASA and NOAA, which
should explain and analyze these phenomena further. After this
efforts yielded no results for months, and the researchers
literally get messed around with this situation, the called these
discharges almost mischievously 'Sprites'.
But after a while and patient effords impressive high speed
filmings succeeded.
By
the way, there is still no definitive plausible explanation for
the origin of Red Sprites, but there are countless theories. One
theory explains that large energetic thunderstorm cells charge
prior to lightning discharge, forming a (-e) leveling layer over
the top of the cell. The initiator is always a
positive!
violent
cloud-to-ground lightning which causes charge shifts (+) in the
upper areas of the thunderstorm cell. Now the overlying (-e) layer
is preserved longer and faces the (+) charged upper ionosphere
(>90km). An quasi oversized electrostatic field is created for a
short time according to the principle of a plate capacitor, which
produces the surge, the so-called red sprite. This electromagnetic
impulse ionizes nitrogen atoms from the stratosphere (<50km) to
the upper thermosphere (90km) and causes them to glow through
fluorescence (cold plasma, fluorescent tube principle or polar
light).
In addition, another theory explains that the luminous phenomenon
could be caused or supported by the cosmic gamma radiation that
always occurs in the ionosphere. The cosmic gamma rays probably
produce an (-e) chain reaction by collision. Thus a high-energy
ion-electron cloud (-e) which reaches into the upper thermosphere
(90km) arises, whereby the typical and unique sprite forms appears. There is
also a
scientific report in the Washington post
which explain some theories.
