Replies

Additional information on sprites. Follow link for additional photos.

http://science.nasa.gov/newhome/headlines/essd23sep98%5F1.htm

These weird flashes were first observed
from the ground, when, quite by accident,
they were captured on video on July 5, 1989
by University of Minnesota scientists John
Winckler, Robert Franz and Robert Nemzek.
The scientists were actually performing a
calibration test for a low light level
monochrome camera, and weren't
particularly looking at the thunderstorm to
the east of their observing site at all. The
next morning, while viewing the test video,
they saw giant twin pillars of light extending
upward more than 30 kilometers above the
thunderstorm.

The flashes were first recorded from space
by the Space Shuttle (STS-34), as it passed
over a highly active thunderstorm in
northern Australia on Oct. 21, 1989. The
shuttle's monochrome TV cameras filmed
what are now called sprites and jets. The
observations were being conducted as part
of the NASA/Marshall Mesoscale Lightning
Observation Experiment. Otha H. Vaughan, Jr.,
of NASA's Global Hydrology Center was the
principal investigator.

In 1994, while flying an extremely sensitive
color camera normally used for auroral
photography in a high altitude aircraft,
University of Alaska scientists confirmed that
the flashes have a generally reddish color
which often fades to purple or blue in the
downward extending tendrils. Dr. Davis
Sentman of UAF named these "sprites" after
the creatures in Shakespeare's "The
Tempest," in part because of their transient,
ephemeral nature. The UAF team also
discovered and named blue jets.

The sprites appear high above the
thunderstorm while the jets shoot out from
the top of the thunderstorm. Sprites appear
to cascade as high as 96 km (60 mi) above
the Earth. Sprites can look like giant red
blobs, picket fences, upward branching
carrots, or tentacled octopi, and can occur
singly or in clusters. The jets appear to be
ejected from the storm top with velocities as
high as 100 km per sec and move up as high
as 32 kilometers.

Stratospheric lightning events could
generate strong electric fields and
electromagnetic pulses which may interact
with the Earth's ionosphere and
magnetosphere. Strong fields at high
altitudes may generate runaway electrons
which could then produce high energy
x-rays and even gamma rays. Thus, it is
possible that lightning may generate a
broad spectrum of electromagnetic
radiation, ranging from extremely low
energy to extremely high-energy gamma
radiation. This theory is supported by the
Burst and Transient Source Experiment
(BATSE) aboard the Compton Gamma Ray
Observatory which has detected gamma
rays coming up from the Earth - not deep
space - when the spacecraft was over
thunderstorms.

Researchers want to know what effect
upward lightning may have on future
commercial aviation operations and high
altitude balloon research flights in the
stratosphere.