A completely new discovery was made in
recent years related to
thunderstorms. It has been observed that far above thunderstorm tops at
altitudes between 50-100km there often occur optical flashes now known
as red sprites and blue
jets . These optical flashes are
very faint and last for only a fraction
of a second, so even if you saw one yourself you would probably think
were dreaming. Other strange lights above thunderstorms have been
halos and trolls. However, we now know that these upper
discharges occur simultaneously with a very specific type of powerful
in the thunderstorm underneath these transient luminous events (TLEs).
powerful lightning flashes that produce the sprites also produce strong
low frequency (ELF) radiation that
can be picked up tens of thousands
of miles away, at our Negev desert ELF station.
We have been involved in a number
of field projects to detect
the electromagnetic signals that are related to
formation, that can be detected in Israel, more than 11,000 km away
from the parent thunderstorms. Below (left) is shown the first
image of a red sprite taken by a team
the University of Alaska, from a research aircraft flying at 15 km
around a thunderstorm in the United States. The black disk at the
of the image (below 20km) is the thunderhead anvil, which blocks out
light from the regular lightning (white light) in the
On the right is one of our black & white sprite images taken with
our cameras in France looking horizontally toward the horizon.
The thunderstorm is a few hundred kilometers away from the camera,
allowing us to see the sprite in the upper atmosphere 50-100km above
Hundreds of thousands of sprites
have now been
documented and studied. They are red in colour due to the
excitation of Nitrogen gas in our atmosphere. The lightning below
the sprites results in large electric fields in the mesosphere (50-100
km altitude) which result in the breakdown of air (mainly N2)
a fraction of a second after the lightning discharge. This
intense lightning discharge also sends radio waves propagating outward
into the earth-ionosphere waveguide in all directions. Hence,
a sprite occurs somewhere on the earth, we receive simultaneously a
wave pulse here in Israel that can be clearly differentiated
all other signals. An example of one of these signals is shown
This signal occurred exactly at the time (within half a second
a sprite was observed optically in the United States. Could
this be a coincidence? Well, besides the time correlation we can
also calculate the direction of arrival of this signal using the 2
components of the magnetic field (not shown). This tells us that
signal arrived from approximately 30 degrees west of north. This
is the great circle angle between Israel and the United States.
using the magnetic and electric fields we can estimate the distance
the lightning/sprite and the observation station. This gives us a
distance of approximately 11,500 km. So with these three bits of
information the signal was found to orignate from the same thunderstorm
observed by our colleagues in the United States. One additional
information we can obtain from the ELF measurements is related to the
type of lightning that produced this pulse. The vertical electric
shows that the initial deviation of the field was POSITIVE, implying a
lightning discharge bringing positive charge to earth (or negative
to the cloud). These are very rare lightnings (less that 5%
but are now known to be the lightnings that produce sprites.
During January 2003 the first
Israeli astronaut, Ilan Ramon, participated in the STS-107 flight of
the Columbia Space Shuttle
as part of the MEIDEX
mission. Part of this mission was to study sprites
from space. While the astronauts photographed the sprites from
we were sitting in the Negev desert, Israel, looking for the radio
related to these events.
Although the Columbia mission ended tragically, the scientific mission
was a great success, with the astronauts observing numerous sprites and
elves from space with calibrated cameras. Our research in the
field of sprites is now dedicated to the memory of
the 7 brave Columbia astronauts. Below we can see an image of an ELVE
and sprite observed from space by the Columbia astronauts. Our
project is called ILAN
after the Israeli astronaut Ilan Ramon.
In the recent few years we
have also started doing laboratory experiments with our colleagues in
Holland to investigate the possiblility of sprites occurring on other
planets. We know that lightning exists on Jupiter and Saturn, and
maybe Venus. If so, we should expect to find also sprites
there. But this depends on the gaseous makeup of planetary
atmospheres, the existence of an ionosphere high enough above the
clouds to allow sprites to form, and low enough gas densitites to allow
for discharges to occur. Such conditions can be produced in a
laboratory, and our findings show that sprites on other planers should
exist. Below are three images of "sprites" in the laboratory on
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Aviv Universtiy coverage of sprite research
Lightning and thunderstorm
at Yucca Ridge
in New Mexico
explanations from Stanford University