This is a continuation of work that uncovered the real complexity of
the activity going on in a thunderstorm. That dark lightning
produces a sharp dose of ionizing radiation is surprising. I also
suspect that this dark lightning could even be in the form of
positively charged ions. We have already understood ball lightning
to be just that and it follows that the more uncommon dark lightning
is just that also.
This provides a much richer understanding of our oldest physical
phenomena that long inspired human curiosity.
This also suggests that passing through a storm will give you a
radiation dose. We should check this out to see if it is significant
and easily detectible.
Thunderstorms
contain ‘dark lightning,’ invisible pulses of powerful radiation
A lightning bolt is
one of nature’s most over-the-top phenomena, rarely failing to
elicit at least a ping of awe no matter how many times a person has
witnessed one. With his iconic kite-and-key experiments in the
mid-18th century, Benjamin Franklin showed that lightning is an
electrical phenomenon, and since then the general view has been that
lightning bolts are big honking sparks no different in kind from the
little ones generated by walking in socks across a carpeted room.
But scientists
recently discovered something mind-bending about lightning: Sometimes
its flashes are invisible, just sudden pulses of unexpectedly
powerful radiation. It’s what Joseph Dwyer, a lightning researcher
at the Florida Institute of Technology, has termed dark lightning.
Unknown to Franklin
but now clear to a growing roster of lightning researchers and
astronomers is that along with bright thunderbolts, thunderstorms
unleash sprays of X-rays and even intense bursts of gamma rays, a
form of radiation normally associated with such cosmic spectacles as
collapsing stars. The radiation in these invisible blasts
can carry a million times as much energy as the radiation in visible
lightning, but that energy dissipates quickly in all directions
rather than remaining in a stiletto-like lightning bolt.
Dark lightning appears
sometimes to compete with normal lightning as a way for thunderstorms
to vent the electrical energy that gets pent up inside their roiling
interiors, Dwyer says. Unlike with regular lightning, though, people
struck by dark lightning, most likely while flying in an airplane,
would not get hurt. But according to Dwyer’s calculations, they
might receive in an instant the maximum safe lifetime dose of
ionizing radiation — the kind that wreaks the most havoc on the
human body.
The only way to
determine whether an airplane had been struck by dark lightning,
Dwyer says, “would be to use a radiation detector. Right in the
middle of [a flash], a very brief bluish-purple glow around the plane
might be perceptible. Inside an aircraft, a passenger would probably
not be able to feel or hear much of anything, but the radiation dose
could be significant.”
However, because
there’s only about one dark lightning occurrence for
every thousand visible flashes and because pilots take
great pains to avoid thunderstorms, Dwyer says, the risk of injury is
quite limited. No one knows for sure if anyone has ever been hit by
dark lightning.
About 25 million
visible thunderbolts hit the United States every year, killing about
30 people and many farm animals, says John Jensenius, a lightning
safety specialist with the National Weather Service in Gray, Maine.
Worldwide, thunderstorms produce about a billion or so lightning
bolts annually.
The conditions for
lightning occur when powerful updrafts in cumulonimbus clouds force
water droplets and ice crystals to rub against one another, creating
massive amounts of positive- and negative-charged particles. The
updrafts cause these two types of charged particles to separate, with
the top of the thundercloud usually becoming positively charged as
the lower part becomes negatively charged.
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