APOD: Red Sprites over the Channel (2017 Jun 15)

Comments and questions about the APOD on the main view screen.
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APOD: Red Sprites over the Channel (2017 Jun 15)

Postby APOD Robot » Thu Jun 15, 2017 4:07 am

Image Red Sprites over the Channel

Explanation: Mysterious and incredibly brief, red sprites are seen to occur high above large thunderstorms on planet Earth. While they have been recorded from low Earth orbit or high flying airplanes, these dancing, lightning-like events were captured in video frames from a mountain top perch in northern France. Taken during the night of May 28, the remarkably clear, unobstructed view looks toward a multicell storm system raging over the English Channel about 600 kilometers away. Lasting only a few milliseconds, the red sprite association with thunderstorms is known. Still, much remains a mystery about the fleeting apparitions including the nature of their relation to other upper atmospheric lightning phenomena such as blue jets or satellite detected terrestrial gamma flashes.

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby Boomer12k » Thu Jun 15, 2017 4:26 am

Awesome to see so many... was that a time lapse or multi-exposure or one shot???

Milliseconds...really too short for a Fireworks show.... but great as a picture!

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby Astronymus » Thu Jun 15, 2017 8:16 am

One wonders if these sprites are caused by high energetic particle radiation from space channeling ionized paths for high voltage discharges into upper atmosphere layers above especialy violent thunder storms.

Boomer12k wrote:Awesome to see so many... was that a time lapse or multi-exposure or one shot???

Milliseconds...really too short for a Fireworks show.... but great as a picture!

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The sprite lasts milliseconds. Therefore this is a long time exposure, no doubt.

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby lhromadka » Thu Jun 15, 2017 9:36 am

Cherenkov radiation by an accelerated particle generated from lightning?

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby Astronymus » Thu Jun 15, 2017 9:48 am

lhromadka wrote:Cherenkov radiation by an accelerated particle generated from lightning?

Cherenkov radiation would be indicated by blue light, wouldn't it?

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby NCTom » Thu Jun 15, 2017 10:41 am

"May 28" link shows a series of photos. Must be a composite. Sure is awesome!

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby neufer » Thu Jun 15, 2017 3:17 pm

Astronymus wrote:
lhromadka wrote:
Cherenkov radiation by an accelerated particle generated from lightning?

Cherenkov radiation would be indicated by blue light, wouldn't it?
https://en.wikipedia.org/wiki/Cherenkov_radiation wrote:
<<Cherenkov radiation results when a charged particle, most commonly an electron, travels through a dielectric (electrically polarizable) medium with a speed greater than the phase velocity of light in that medium. The characteristic blue glow of an underwater nuclear reactor is due to Cherenkov radiation.>>

50 MeV electrons are fast enough to produce some very weak Cherenkov radiation in the Tropopause but GeV electrons would be required to produce Cherenkov radiation in the rarefied Mesosphere. Such GeV electron energies would be marginal even with billion volt cumulonimbus positive potential differentials due to electron collisions with molecules (on the way down) producing the observed sprite florescence.

https://en.wikipedia.org/wiki/Cosmic_ra ... on_methods wrote:
<<IACT stands for Imaging Atmospheric Cherenkov Telescope. It is a device or method to detect very-high-energy gamma-ray photons in the energy range of 50 GeV to 50 TeV.

The IACT works by imaging the very short (5 to 20 ns) flash of Cherenkov radiation generated by the cascade of relativistic charged particles produced when a very-high-energy gamma ray strikes the atmosphere. This shower of charged particles, known as an Extensive Air Shower (EAS), is initiated at an altitude of 10–20 km. The incoming gamma-ray photon undergoes pair production in the vicinity of the nucleus of an atmospheric molecule. The electron-positron pair produced are of extremely high energy and immediately undergo Bremsstrahlung or "Braking Radiation". This radiation produced is itself extremely energetic, with many of the photons undergoing further pair production. While these telescopes are extremely good at distinguishing between background radiation and that of cosmic-ray origin, they can only function well on clear nights without the Moon shining.>>
Last edited by neufer on Thu Jun 15, 2017 3:35 pm, edited 1 time in total.
Art Neuendorffer

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby neufer » Thu Jun 15, 2017 3:32 pm

https://en.wikipedia.org/wiki/Johann_Georg_Estor wrote:
<<Johann Georg Estor (6 June 1699 – 25 October 1773), was a German theorist of public law, historian and book collector. In the second volume of his "neue kleine Schriften" there is a little note, in which Estor says that he had explored the landscapes of Hessen-Darmstadt on horseback or walking to accomplish a book about the national geography of this county. This was in the years around 1730. His teachers Verdrieß and Johann Jakob Scheuchzer had given him a hint, to make observations "coelo tristi" (in a sad sky). So, following this hint, he one day went uphill one of the highest mountains in the Vogelsberg near Burgharts, called "the saddle", through a thundercloud. In the middle of the cloud he felt little water droplets on his skin like dew. And as he had reached the top of the mountain, he saw the blue sky above him and the cloud beneath like a white sea, from which flashes mounted as well directly up into the sky and shot down to the earth.>>
https://en.wikipedia.org/wiki/Sprite_(lightning) wrote:
<<Sprites are large-scale electrical discharges that occur high above thunderstorm clouds, or cumulonimbus, giving rise to a quite varied range of visual shapes flickering in the night sky. They are triggered by the discharges of positive lightning between an underlying thundercloud and the ground.

Sprites appear as luminous reddish-orange flashes. They often occur in clusters within atmosphere above the troposphere at an altitude range of 50–90 km. Sporadic visual reports of sprites go back at least to 1886, but they were first photographed on July 6, 1989 by scientists from the University of Minnesota and have subsequently been captured in video recordings many thousands of times.

Sprites are sometimes inaccurately called upper-atmospheric lightning. However, sprites are cold plasma phenomena that lack the hot channel temperatures of tropospheric lightning, so they are more akin to fluorescent tube discharges than to lightning discharges.>>
https://en.wikipedia.org/wiki/Lightning ... _lightning wrote:
<<Most cloud-to-ground (CG) lightning is negative, meaning the ground is more positive. Large bolts of lightning can carry up to 120 kA and 350 coulombs (2.2 ×1021 protons).

Unlike the far more common "negative" lightning, positive lightning originates from the positively charged top of the clouds (generally anvil clouds) rather than the lower portion of the storm. Leaders form in the anvil of the cumulonimbus and may travel horizontally for several kilometers before veering towards the ground. A positive lightning bolt can strike anywhere within several kilometers of the anvil of the thunderstorm, often in areas experiencing clear or only slightly cloudy skies; they are also known as "bolts from the blue" for this reason. Positive lightning typically makes up less than 5% of all lightning strikes.

Because of the much greater distance to ground, the positively charged region can develop considerably larger levels of charge and voltages than the negative charge regions in the lower part of the cloud. Positive lightning bolts are considerably hotter and longer than negative lightning. They can develop six to ten times the amount of charge and voltage of a negative bolt and the discharge current may last ten times longer. The potential at the top of the cloud may exceed a billion volts — about 10 times that of negative lightning. During a positive lightning strike, huge quantities of extremely low frequency (ELF) and very low frequency (VLF) radio waves are generated. As a result of their greater power, as well as lack of warning, positive lightning strikes are considerably more dangerous. At the present time, aircraft are not designed to withstand such strikes, since their existence was unknown at the time standards were set, and the dangers unappreciated until the destruction of a glider in 1999.

Positive lightning has also been shown to trigger the occurrence of Upper-atmospheric lightning between the tops of clouds and the ionosphere. Positive lightning tends to occur more frequently in winter storms, as with thundersnow, during intense tornadoes and in the dissipation stage of a thunderstorm.>>
Art Neuendorffer

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby MarkBour » Thu Jun 15, 2017 10:33 pm

Thanks, Art. Very enlightning. :-)

Why do the sprites appear sharper at the bottom and then soft and diffuse at the top?
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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby neufer » Fri Jun 16, 2017 12:16 am

MarkBour wrote:
Why do the sprites appear sharper at the bottom and then soft and diffuse at the top?

    I'm guessing a Z-pinch:
https://en.wikipedia.org/wiki/Pinch_(plasma_physics)#The_.CE.B8-pinch wrote:
<<A pinch is the compression of an electrically conducting filament by magnetic forces. The conductor is usually a plasma, but could also be a solid or liquid metal. Pinches were the first device used by humankind for controlled nuclear fusion. Pinches occur naturally in electrical discharges such as lightning bolts, the aurora, current sheets, and solar flares.

The Z-pinch has a magnetic field in the θ direction and a current "J" flowing in the "z" direction. The first creation of a Z-pinch in the laboratory may have occurred in 1790 in Holland when Martinus van Marum created an explosion by discharging 100 Leyden jars into a wire. The phenomenon was not understood until 1905, when Pollock and Barraclough investigated a compressed and distorted length of copper tube from a lightning rod after it had been struck by lightning. Their analysis showed that the forces due to the interaction of the large current flow with its own magnetic field could have caused the compression and distortion.

In 1958, the worlds' first controlled thermonuclear fusion experiment was accomplished using a theta-pinch machine named Scylla I at the Los Alamos National Laboratory. A cylinder full of deuterium was converted into a plasma and compressed to 15 million degrees Celsius under a theta-pinch effect. Lastly, at Imperial College in 1960, led by R Latham, the Plateau-Rayleigh instability was shown, and its growth rate measured in a dynamic Z-pinch.>>
Art Neuendorffer

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby Catalina » Fri Jun 16, 2017 4:51 pm

If you click on "captured in video frames" in the caption, the link will take you to video versions of the image, and they are SPECTACULAR. The videos show the sprites as they happened, milliseconds, and then slowed down so that the viewer can see the progression of the sprite formation. It's absolutely fascinating to watch these!

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby Guest » Fri Jun 16, 2017 9:14 pm

A mountain top perch in northern France? Flat as a pancake! Eastern France, Southern France - even the middle of France, but that dreary northern plain is, well, a plain....! Never mind - spectacular images, well caught. Are the lights those of Paris? the Channel coasts? What direction are we looking from Vosges?

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby neufer » Fri Jun 16, 2017 10:14 pm

Guest wrote:
A mountain top perch in northern France? Flat as a pancake!
Eastern France, Southern France - even the middle of France, but that dreary northern plain is, well, a plain....!

"Northern France [with an] unobstructed view toward a multicell storm
system over the English Channel about 600 kilometers away."
Art Neuendorffer

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Re: APOD: Red Sprites over the Channel (2017 Jun 15)

Postby rstevenson » Sat Jun 17, 2017 12:34 am

Guest wrote:A mountain top perch in northern France? Flat as a pancake! Eastern France, Southern France - even the middle of France, but that dreary northern plain is, well, a plain....! ...

It's approximately 550km from Le Havre (on the Channel) to the Balon des Vosges Natural Regional Park, where there's a decent mountain. And that's definitely in northern France. If it must be 600km, then I guess you're going to be on the flanks of the Alps, maybe not far from Basel, Switzerland (but still in France.)

Rob


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