sprites, elves, trolls, pixies, gnomes and other strange things
TRANSCRIPT
Sprites, Elves, Trolls, Pixies, Gnomes and Other Strange Things Found In Our Atmosphere Joseph R. Dwyer Department of Physics and Space Science Center, University of New Hampshire
Courtesy Steve Cummer
Sprite as it would appear from across the state of Kansas
moon
Courtesy Steve Cummer
Sprites are high-altitude discharges above thunderstorms
They are caused by powerful lighting flashes near the ground.
They come in various shapes and sizes
Human-Resonance.org
They come in various shapes and sizes
Human-Resonance.org
They come in various shapes and sizes
Human-Resonance.org
They come in various shapes and sizes
Human-Resonance.org
Many of the long filamentary structures seen are actually moving balls of light
McHarg et al. 2010
Streamers • Spites are not like ordinary
lightning, since they do not have hot channels.
• Streamers are propagating
discharge structures. • They carry current electric current
without heating the air very much. • Computer simulations (right)
show us how they work.
The breakdown voltage of air is much lower at high altitudes
• A 12 V battery cannot create an electrical discharge (i.e. a spark) at sea-level pressures.
• That same voltage
would discharge at the pressures where sprites live.
electricalfun.com
The charge motion caused by lightning makes sprites
Grant W. Petty
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The pressures are very low up here and so even
small voltages can make a discharge
• A large positive cloud-to-ground lightning flash can transfer large amounts of positive charge to the ground, leaving negative charge in the cloud.
• The air above the thunderstorm
feels this negative charge, resulting in a voltage in the upper atmosphere.
• Just above the cloud this voltage is
too small to make a discharge. • At about 70 km, the pressure is low
enough so that a streamer discharge forms, making a sprite.
Weird lightning: exhibit A Transient Luminous Events (TLEs)LE
NOAA National Severe Storms Laboratory, adapted from Carlos Miralles (AeroVironment) and Tom Nelson (FMA).
ELVES stands for
Emissions of Light and Very Low Frequency Perturbations due to Electromagnetic Pulse
Sources
Rapidly expanding ring of light in the lower ionosphere. Caused by the electromagnetic radiation from lightning near the ground.
Jets
(Gigantic jets, blue jets and blue starters) These are forms of upward lightning.
Pixies, Gnomes and TROLLs (for Transient Red Optical Luminous Lineament)
NOAA National Severe Storms Laboratory, adapted from Carlos Miralles (AeroVironment) and Tom Nelson (FMA).
Pixies and Gnomes
TROLLs
There are other weird thing in our atmosphere: Compact Intracloud Discharges (CIDs)
Photo by Mindi Holcomb
Volcanic Lightning (If the volcano doesn’t get you, the lightning will.)
Source Daily Mail Online
Superbolts (big, bad lightning) 100 times brighter than normal lightning
http://www.erh.noaa.gov/lwx/lightning/va-lightning.htm
Superbolts are similar to lightning on Jupiter (Big Planet = Big Lightning)
Courtesy NASA
Sympathetic lightning
Courtesy NASA
Spider lightning
From http://www.flickr.com
Heat lightning
http://en.wikipedia.org/wiki/Heat_lightning
Bead Lightning As the bright return stroke channel decays, it can break apart into longer lasting beads of light
Ribbon Lightning
Wind blows the subsequent channels sideways
Image via: Disaster Strikes
Rocket-triggered lightning
Credit UF
X-rays from lightning
From Scientific American, May 2005
Thunderstorms glow in gamma-rays.
Dwyer, Smith and Cummer (2012)
DailyGalaxy.com
Gamma-Ray glows recorded by ADELE
NCAR/NSF GV
CGRO/BATSE Terrestrial Gamma-ray Flash (TGF) (Fishman et al. 1994)
http://www.batse.msfc.nasa.gov/batse/tgf/
Explosive production of energetic particles
Terrestrial gamma-ray flash (TGF)
and electron-positron beam seen from space
Courtesy NASA
Courtesy NASA
Terrestrial gamma-ray flash (TGF)
and electron-positron beam seen from space
Global distribution of TGFs seen by RHESSI
Figure from Splitt et al. (2010)
Where do they come from?
http://www.holoscience.com/news/balloon.html http://www.holoscience.com
Where do they come from?
http://www.holoscience.com
1994 – 2005: Here
Where do they come from?
http://www.holoscience.com/news/balloon.html
1994 – 2005: Here
After 2005: Here
http://www.holoscience.com
How do thunderstorms make
terrestrial gamma-ray flashes?
There are two leading models: • Lightning leader emission, similar to x-ray
emission seen near the ground. • Dark Lightning!
Dark Lightning The central avalanche is due to the injection of a single, 1 MeV seed electron. All the other avalanches are produced by x-ray and positron feedback. The top panel is for times, t < 0.5 µs. The middle panel is for t < 2 µs, and the bottom panel is for t < 10 µs.
From Dwyer (2007)
Dark lightning
• A new kind of lightning. • Generates so many high-energy particles that it
discharges the thunderstorm faster than normal lightning.
• Makes currents as big as normal lightning, e.g. > 100,000 amps.
• Emits very little visible light, i.e. appears dark. • Can explain TGFs. • Cosmic rays are not needed.
Multi-pulsed TGFs
From Dwyer (2012)
CGRO/BATSE TGFs
Multi-pulsed TGFs
Dark lightning model result
From Dwyer (2012)
CGRO/BATSE TGFs
Dark Lightning • A new kind of lightning • Among the most powerful discharges on the planet • Invisible to the human eye • Makes TGFs as a by-product
• A radiation hazard for airline passengers and crew • First identified in 2012
The name “dark lightning” was introduced over 100 years ago to describe the Clayden effect, seen in photographs of lightning.
Dark Lightning
August 2012 Scientific American
Radiation doses received by individuals inside aircraft struck by a TGF
From Dwyer et al. (2010)
Wikimedia Commons
And of course ball lightning is very weird.
Summary
• There are many strange things in our atmosphere that
we are just now learning about. • Who knows what other interesting things we will find
if we just look. • We understand the insides of stars halfway across the
universe better than we understand the insides of thunderstorms 5 miles over our heads.