Team makes breakthrough in understanding rare lightning-triggered gamma-rays

May 17, 2018, University of Utah
A Telescope Array Surface Detector and its neighbors, deployed in Utah's west desert. The 507 detectors are arranged on a grid covering 700 square kilometers, about the same as the land area of New York City. Credit: Telescope Array collaboration

In the western Utah desert, the Telescope Array sprawls across an area the size of New York City, waiting for cosmic rays. The facility detects the high-energy particles that collide with Earth's atmosphere constantly; the cosmic rays trigger the 500-plus sensors once every few minutes.

While pouring over data in 2013, Telescope Array physicists discovered a strange particle signature; the photon equivalent of a light drizzle punctuated by a fire hose. The had unexpectedly recorded an extremely rare phenomenon—, the highest-energy light waves on the electromagnetic spectrum, produced by lightning strikes that beam the radiation downward toward the Earth's surface. Five years later, an international team led by the Cosmic Ray Group at the University of Utah has observed the so-called downward terrestrial gamma ray flashes (TGFs) in more detail than ever before.

The Telescope Array detected 10 bursts of downward TGFs between 2014 and 2016, more events than have been observed in rest of the world combined. The Telescope Array Lightning Project is the first to detect downward TGFs at the beginning of cloud-to-ground lightning, and to show where they originated inside thunderstorms. The Telescope Array is by far the only facility capable of documenting the full TGF "footprint" on the ground, and show that the gamma rays cover an area 3 to 5 km in diameter.

"What's really cool is that the Telescope Array was not designed to detect these," said lead author Rasha Abbasi, researcher at the High-Energy Astrophysics Institute and the Department of Physics & Astronomy at the U. "We are 100 times bigger than other experiments, and our detector response time is much faster. All of these factors give us the ability that we weren't aware of—we can look at lightning in a way that nobody else can."

The study published online on May 17 in The Journal of Geophysical Research: Atmospheres.

An accidentally perfect laboratory

The work builds on a study published by the group last year that established a strong correlation between similar bursts of energetic particle showers detected between 2008 and 2013, and lightning activity recorded by the National Lightning Detection Network. The physicists were stunned.

"It was BOOM BOOM BOOM BOOM. Like, four or five triggers of the detectors occurring within a millisecond. Much faster than could be expected by cosmic rays," said John Belz, professor of physics at the U and principal investigator of the National Science Foundation-funded Telescope Array Lightning Project. "We realized eventually that all of these strange events occurred when the weather was bad. So, we looked at the National Lightning Detection Network and, low and behold, there would be a lightning strike, and within a millisecond we would get a burst of triggers."

The researchers brought in lightning experts from the Langmuir Laboratory for Atmospheric Research at New Mexico Tech to help study the lightning in more detail. They installed a nine-station Lightning Mapping Array developed by the group, which produces 3-D images of radio-frequency radiation that lightning emits inside a storm. In 2014, they installed an additional instrument in the center of the array, called a "slow antenna", that records changes in the storm's electric charge caused by the lightning discharge.

A bolt of insight
The bright flash of light is only one stage of lightning; there's a substructure that happens too fast for the eye to see. 'Step leaders' proceed toward the ground in stages. Negative electric charge builds at the leader tip until it is sufficient to cause the air to break down and form a new conducting path. The study found that terrestrial gamma rays are produced within the first 1-2 milliseconds of the initial breakdown stage, which is the least understood part of lightning. Credit: National Oceanography and Atmospheric Administration
"Taken together, the Telescope Array detections and the lightning observations constitute a major advance in our understanding of TGFs. Prior to this, TGFs were primarily detected by satellites, with little or no ground based data to indicate how they are produced", said Paul Krehbiel, long-time lightning researcher at the New Mexico Institute of Mining and Technology and co-author of the study. "In addition to providing much better areal coverage for detecting the gamma rays, the array measurements are much closer to the TGF source and show that the gamma rays are produced in short duration bursts, each lasting only ten to a few tens of microseconds."

An extremely rare phenomenon

Until a FERMI satellite recorded the first TGF in 1994, physicists thought only violent celestial events, such as exploding stars, could produce gamma rays. Gradually, scientists determined that the rays were produced in the initial milliseconds of upward intracloud lightning, which beamed the rays into space. Since discovering these upward TGFs, physicists have wondered whether cloud-to-ground lightning could produce similar TGFs that beam downward to the Earth's surface.

Previously, only six downward TGFs have ever been recorded, two of which came from artificially-induced lightning experiments. The remaining four studies with natural lightning report TGFs originating much later, after the lightning had already struck the ground. The array's observations are the first to show that downward TGFs occur in the initial breakdown stage of lightning, similar to the satellite observations.

"The downward-going TGFs are coming from a similar source as the upward ones. We safely assume that we have similar physics going on. What we see on the ground can help explain what they see in the satellites, and we can combine those pictures in order to understand the mechanism of how it happens," said Abbasi.

"The mechanism that produces the gamma rays has yet to be figured out," added Krehbiel.

What's next

The researchers have many questions left unanswered. For example, not all create the flashes. Is that because only one particular type of lightning initiation produces them? Are the scientists only seeing a subset of TGFs that happen to be large enough, or point in the right direction, to be detected?

The team hopes to bring additional sensors to the Telescope Array to enhance the lightning measurements. In particular, installing a radio-static detecting "fast antenna" would enable the physicists to see the substructure in the electric field changes at the beginning of the flash.

"By bringing other types of detectors and expanding the effort, I think we can become a significant player in this area of research," said Belz.

Explore further: NASA's Firestation on way to the International Space Station

More information: R. U. Abbasi et al, Gamma-ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders, Journal of Geophysical Research: Atmospheres (2018). DOI: 10.1029/2017JD027931

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1 / 5 (10) May 17, 2018
I hope these results and explorations for their explanation are coordinated with LIGO and other teams chasing the Gravitational Waves (GW) especially with 7/2017 assumed NeutronStar merge where the afterglow of GRB source got 4-fold brighter vs. weaker as expected. Also, the related recent work on disturbances in magneto/ionos-sphere caused by solar wind or Coronal Mass Ejection bursts appear connected to the observed TGF results.
5 / 5 (7) May 17, 2018
I hope these results and explorations for their explanation are coordinated with LIGO and other teams chasing the Gravitational Waves (GW) especially with 7/2017 assumed NeutronStar merge where the afterglow of GRB source got 4-fold brighter vs. weaker as expected. Also, the related recent work on disturbances in magneto/ionos-sphere caused by solar wind or Coronal Mass Ejection bursts appear connected to the observed TGF results.

You have data temporally connecting their measured spikes with Coronal activity reaching Earth? Please share! I don't know why you would keep this to yourself!
Da Schneib
4.4 / 5 (7) May 17, 2018
@691, no kidding. Correlations with either solar wind fluctuation or CME arrival would be extremely significant; since the data are all public (freely available for this paper at the DOI link in this article as "supporting information" and freely available online for CMEs and solar wind fluctuations) this shouldn't be a difficult task. But I seriously doubt anyone will find anything here. Looks like more Thunderdolts BS to me, suspiciously similar to "god of the gaps" arguments about evolution and molecular biology.
1 / 5 (10) May 17, 2018
My fields of surveying mathematics in photogrammetry (based on conformal invariance like quantum theory) and physical & geometric geodesy (math modeling of geoid and computational GPS technologies) agree with the dynamic bouncing model of Suntola Dynamic Universe (DU). It can explain the controversies of Earth vs Sun centered world view 400 years ago and its recent repeat of Dark Energy (DE) mistake of GRT to explain SN1a data in the more cosmic scale of BB vs. DU centered view. The latest (Nobel rewarded) premature interpretation of Gravitational Waves (GW) appears to keep repeating the same basic flaw of estimation theory. So what could explain LIGO reported GW data? cont.
4.2 / 5 (10) May 17, 2018
So what could explain LIGO reported GW data?

A neutron star merger. As predicted. And as confirmed by the follow-up observations. No need for any woo.
Da Schneib
3.8 / 5 (10) May 17, 2018
@Anon, we're not interested in your theories of the universe nor in your claims to expertise that doesn't seem to have anything to do with the subject at hand. Either you can look at the publicly available data and substantiate your conjecture or you cannot, and unless you've got something more than what you just said you cannot. And that's the only thing that matters.
3.8 / 5 (10) May 17, 2018
I'd be very interested in what could trigger a detection in Washington state, Louisiana and Italy, with minute differences in time and direction that allowed them to triangulate to a place in the sky where, tadaaaa, they saw pretty much what was predicted for a neutron star merger.
That would be some trick.
1.4 / 5 (9) May 17, 2018
LIGO principle assumes the 4-D GW arriving perpendicular to the 2-D x,y tube planes of interferometers where the mirrors are isolated from the surrounding EM bound matter, no surrounding feeble gravitational interaction of GW should overpower the strong atomic force to move them. But once the DU strain resolution of 10^-21/ms (DU deceleration rate of expansion C4 of Riemann 4-radius R4) was reached by the incredible leap of LIGO side-band circulation of 75-284 Hz, LIGO eliminated the 3-D uniform background strain - and became fair victim to local sources of imitators (like BICEP2 project) of the assumed GR based GW strain shapes of BH or Neutron Star merges. Especially with the precursor and echo correlation problems, potentially caused by the solar wind and CME bursts masking the real or assumed GRB sources. See DU books and papers since 1995 for other reasons (like slow-down of atomic clock frequency) to explain LIGO 'apparent' x,y affine scale changes of EM bound matter.
4.1 / 5 (9) May 17, 2018
^^^^^^^Bollocks. That is pure word salad. How is it causing the same effect in three separate places? And when they triangulate that signal they see a neutron star merger. Not assumed. Confirmed as near as makes no difference, including the predicted r-process nucleosynthesis. Whatever the hell DU is, did it predict that? And where do you think a frigging CME would triangulate to? Have a think about that one. Sorry, just another physics crank whose world has been screwed up by real scientists doing real science. Tough, get over it, and find a woo forum to post your nonsense on.
1 / 5 (6) May 17, 2018

Tadaa, the triangulated direction was so close to the Sun that x-ray observations had to be interrupted and 16 days later when the assumed GRB location again became clearly visible, its EM radiation intensity was INCREASED 4-fold vs the expected decrease. As if some local CME or other occlusion during its 130 M year travel path had cleared. The short BH merge GW imitations can be explained by the precursor and echo correlation bias in the fashion of serial correlation of pre-GPS range sensing systems in geodesy and self-calibration technologies of aerial and satellite photogrammetry in 1970's.
1.4 / 5 (10) May 18, 2018
Useless clickbait article, the author should retire.
5 / 5 (6) May 18, 2018
Useless clickbait article, the author should retire.

Did you even read the article? I feel the title and content match, and it was kind of interesting. What makes it clickbait?
1 / 5 (7) May 18, 2018
Electric discharge as the source of gamma rays, here on Earth and in the Cosmos as well.
1 / 5 (6) May 18, 2018
This local EM event of TGF could have triggered the GRB alert followed by the initial assumed NS GW trigger 0.7 sec later. The global DU energy balance principle rules out the original GRT based GW explanation even at the assumed more local 130 M l.y distance of NS merge (vs. BH merges at 1-3 B l.y distances) in terms of Mach principle, see Suntola slide presentation 3/2016. Note that in GRT based cosmology of zero or accelerated expansion (due to Dark Energy blessing of 2011 SN1a Nobel interpretation), LIGO could never resolve GWs with its present DU based deceleration limit dC4/C4 of 10^-22/ms.
4.1 / 5 (9) May 18, 2018
^^^^^^^^WTF is that nonsense? This is an article about gamma rays from terrestrial lightning. What the hell has that got to do with neutron star mergers creating GWs 130 m ly away? Nothing whatsoever, would be the answer to that. And what is suntola? Some kind of yoghurt?
3.7 / 5 (6) May 18, 2018
Electric discharge as the source of gamma rays, here on Earth and in the Cosmos as well.

Nope. What electric discharges in the cosmos?
5 / 5 (4) May 19, 2018
Thor and his 130 million light year lightning bolts
Typically Norse
cantdrive> Electric discharge as the source of gamma rays, here on Earth and in the Cosmos as well.

jonesdave> Nope. What electric discharges in the cosmos?

This electrical discharge in gamma rays is powerful, stuff it not only attracts the fluff down here on little old blighty, but on stars 130 million light years away. Thor would be really impressed with this Lightning bolt reaching 130million light years irradiating Earth with its impressive gamma rays.
Thor is enrolling in an Electrical Woo masters at Cambridge University.
1 / 5 (1) May 22, 2018
FYI, Dr Tuomo Suntola (the founder of Physics Foundations Society and the unified quantum & relativity theory of Dynamic Universe) was awarded today 1 M euro Millenium Prize by President Niinisto for Suntola's early industrial inventions of the atomic layer technology. His more monumental work on DU has evolved since his HUT (home of Prof. Nordstrom, inventor of relativity before Einstein) doctoral work in 1970's and 1995 DU break-through. It is documented by journal papers (often presented at international conventions of PIRT, SPIE etc. expert groups) and today collected at his web site for public view.
not rated yet May 22, 2018
It can explain the controversies of Earth vs Sun centered world view 400 years ago and its recent repeat of Dark Energy (DE) mistake of GRT to explain SN1a data in the more cosmic scale of BB vs. DU centered view.

What do you mean by BB vs DU? I believe that DU also starts with BB, the universe is just a lot younger.
1 / 5 (1) May 23, 2018
BB assumes the universe started 13.8 B years ago with an eternally constant speed of light C independent of the inflationary expansion rate C4 of the metric 4-radius R4, today at 13.8 B l.y. The latest DU bounce or cool 'Little Bang' took place 9.2 B years ago at high speeds of C and C4 and small values of R4 by continually balancing the positive motion energy of total mass M in universe with its total negative gravitational energy. Even a 5th grader can derive the resulting nonlinear functions among C, C4, R4 and scalar Newtonian absolute time T4 with today's reduced ticking rate. The locally observable C_obs in EM bound matter appears constant, explaining recent Nobel level mistakes to model DE and GW data, see Suntola's books and papers. You are right about possible repeat bounces of DU. No need today to worry about the first contraction of bounce as we need to correct the mistakes of GR and QM in cosmic and particle theories of physics foundations.
not rated yet May 23, 2018
Maybe it's just me, the daffy knucklehead that I am....but...
isn't something missing here?
There are known stochastic health risks from exposure to upward TGFs while flying through a thunderstorm.
With a similar source as upward TGFs and a footprint of 3 to 5 kilometers, are not downward TGF doses a concern of potential threat to one's immediate well-being?
1 / 5 (1) May 24, 2018
This is a link to Dr Suntola interview about the background of ALD nano-technology and related Dynamic Universe rethinking of physics foundations like GR and QM theories.

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