Friday, May 5, 2023

3984 - LIGHTNING BOLTS - can become superbolts?

 

-   3984  - LIGHTNING  BOLTS  -  can become superbolts?   Lightning forms when electrical charges in clouds and on the ground interact, and in most of these events the clouds are negatively charged. However, superbolts form during rare cloud-to-ground interactions in which the clouds are positively charged.


------------  3984  -   LIGHTNING  BOLTS  -  can become superbolts?

-  Lightning bolts or  flashes of lightning that are up to 1,000 times brighter than average do exist.  After evaluating years of data, scientists confirmed these ultrabright bolts can produce at least 100 gigawatts of power.  To put that into perspective, the power produced by all the solar panels and wind turbines in the United States in 2018 was about 163 gigawatts.

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-   “Superbolts” are lightning flashes that were over 100 times more intense than typical lightning.  Lightning data for that study came from observations by “Vela satellites”, which were launched in 1969 to detect nuclear explosions from space, and operated until 1979.

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-    Vela's instruments recorded thousands of lightning strikes per year, including superbolts that struck around the world with most frequent occurrence over the North Pacific Ocean.

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-    One superbolt flash near South Africa in 1979 was so powerful that it was thought to be the detonation of a nuclear bomb.  Another superbolt that struck Newfoundland in 1978 left a one‐mile swath of damage in its wake.

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-    Trees were split; television antennas were twisted beyond recognition; transformers were shattered and circuit breakers hung from power‐line poles, and there were craters in the new‐fallen snow.

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-   Superbolts are  super-rare, occurring only about five times in 10 million flashes.   In the southeastern United States on February 19, 2019, the lightning flash spanned several hundred kilometers and lasted nearly 7 seconds. 

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-     Research focused on superbolts that are substantially brighter than normal lightning — at least 100 times more energetic — and then looked at the top pulses above that threshold, with the top cases even going beyond 1,000 times brighter.

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-   Using the “Fast On‐Orbit Recording of Transient Events” (FORTE) satellite scientisrs learned that certain viewing conditions did affect lightning brightness, when the satellite's view was unobstructed by clouds, a bolt could appear somewhat brighter, and some suspected superbolt observations did fall into that category.

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-    GLM and FORTE are both optical instruments, but they measure slightly different aspects of lightning pulses.  FORTE recorded instantaneous peak power of the superbolts, the moment they were at their brightest.

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-     By comparison, GLM measured superbolts' total energy over a 2-microsecond period. That might not seem like very long, but it is for lightning, where much of the activity happens at microsecond scales.

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-   The scientists found that superbolts could emanate from electrical pulses between clouds, as well as from cloud-to-ground pulses. Superbolts that appeared over the ocean were fueled by the gradual buildup of electrical charges in the stormclouds.  These bolts would be more powerful when all that electricity was eventually released.

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-    The brightest superbolts tended to cluster in geographic regions where large thunderstorms are common, and superbolt appearance was associated with "long-horizontal lightning flashes” that can span hundreds of kilometers, which have been recently termed 'megaflashes”.

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-     'Gigantic jet'  shot into space may be the most powerful lightning bolt ever detected.  These lightning bolts blasting out of the top of a cloud over Oklahoma, and shooting directly into space.

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-   Instead of striking down toward the ground, or zipping sideways between clouds, this lightning bolt does something unexpected: It blasts straight upward from the top of the cloud, shooting 50 miles into the sky, grazing the lower edge of space.

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-   These are gigantic jets the rarest and most powerful sort of lightning, occurring as few as 1,000 times a year and emitting more than 50 times as much energy as a typical lightning bolt.

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-     By studying the jet's radio-wave emissions using satellite and radar data, researchers learned that the bolt moved approximately 300 coulombs of energy from the top of the cloud to the lower ionosphere, the layer of charged particles that separates Earth's upper atmosphere from the vacuum of space, or roughly 60 times the 5-coulomb output of a typical lightning bolt.

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-   The charge transfer is nearly double the previous largest by a gigantic jet and is comparable to the largest ever recorded for cloud-to-ground strokes.

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-   Capturing such detailed data on the massive stroke of lightning required an equally massive stroke of luck. A citizen scientist based in Hawley, Texas filmed the jet with a low-light camera on May 14, 2018, watching as the gargantuan discharge shot out of a cloud top before connecting with charged particles in the ionosphere, some 60 miles above the ground.

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-    Scientists analyzing the footage found that, as luck would have it, the jet occurred very near the center of a large lightning mapping array (LMA), a network of ground-based radio antennas used to map the locations and times of lightning strikes. The jet was also within range of several weather radar systems, as well as a weather-watching satellite network.

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-    With these sources combined, the researchers studied the size, shape and energy output of the gigantic jet in unprecedented detail. The researchers found that the jet's highest-frequency radio-wave emissions (the kind that LMAs are built to detect) came from small structures called streamers, which develop at the very tip of a lightning bolt and create a "direct electrical connection between the cloud top and the lower ionosphere.

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-    The strongest electric current, meanwhile, flowed considerably behind the streamers, in a section called the “leader”. The data also showed that while the streamers were relatively cool, with a temperature of roughly 400 degrees Fahrenheit, the leader was scorching hot, with a temperature of more than 8,000 degrees F. This discrepancy is true of all lightning strikes, not just gigantic jets.

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-   Why does lightning sometimes blast up instead of down? Scientists still aren't totally clear on that, but it likely involves some sort of blockage that prevents lightning from escaping through the bottom of a cloud; gigantic jets are typically observed in storms that don't produce many cloud-to-ground lightning strikes.

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-   There is usually a suppression of cloud-to-ground discharges.  In the absence of the lightning discharges we normally see, the gigantic jet may relieve the buildup of excess negative charge in the cloud.

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-    More research — and a lot more luck — is needed to understand these epic, upside-down lightning strikes.

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                  May 3, 2023      LIGHTNING  BOLTS  -  can become superbolts?       3984                                                                                                                        

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