Weak gamma-ray glows from thunderclouds may precede lightning bolts and accompanying gamma-ray flashes.
A thundercloud can carry over 1 billion volts of electricity (Wada, 2019)
A University of Tokyo graduate student — Yuuki Wada-- together with colleagues from Japan, has discovered a connection between lightning strikes and two kinds of gamma-ray phenomena in thunderclouds. Their research suggests that, in certain conditions, weak gamma-ray glows from thunderclouds may precede lightning bolts and their accompanying gamma-ray flashes. For around three decades, scientists have been aware that thunderstorms can bring with them gamma-ray activity. As Wada explains: “Forever, people have seen lightning and heard thunder. These were the ways we could experience this power of nature.“With the discovery of electromagnetism, scientists learned to see lightning with radio receivers. But now we can observe lightning in gamma rays — ionizing radiation. It’s like having four eyes to study the phenomena.”
Gamma-ray glow preceding gamma-ray flash. (Yuuki Wada and Hayanon’s Science Manga Studio, 2019)
There are two known kinds of gamma-ray phenomena associated with thunderclouds — gamma-ray glows, which are weak emissions lasting about a minute, and the short-lived and far more intense terrestrial gamma-ray flashes (TGFs). The latter of these phenomena manifests as lightning strikes.
Both of these aspects manifest in regions of thunderclouds sandwiched between layers of varying charge. In these charged regions, electrons are accelerated to speeds approaching that of light. At these relativistic speeds, electrons that stray very close to the nuclei of nitrogen atoms in the air. The electrons slow down a little and emit a telltale gamma ray — known as bremsstrahlung radiation.
The radiation levels of the gamma-ray flashes are quite low — roughly a tenth of what one would expect to receive from a typical medical X-ray.
To measure this phenomenon, Wada and colleagues worked with local schools and businesses to install radiation monitors onto various buildings in the city of Kanazawa, Ishikawa Prefecture, in central Japan. These radiation monitors form a network which is able to detect radiation coming from the sky.
Wada continues: “During a winter thunderstorm in Kanazawa, our monitors detected a simultaneous TGF and lightning strike. This is fairly common, but interestingly we also saw a gamma-ray glow in the same area at the same time.
“Furthermore, the glow abruptly disappeared when the lightning struck. We can say conclusively the events are intimately connected and this is the first time this connection has been observed.”
A thundercloud over the city of Kanazawa. The gamma-ray glow terminated abruptly around location B. The lightning struck between locations A and B.(Wada, 2019)
The mechanism underlying lightning discharge is highly sought after and this research could reveal previously unknown insights. Wada and team intend to further their investigation to explore the possibility that gamma-ray glows don’t just precede lightning strikes — but may actually cause them.
Wada continues: “Our finding marks a milestone in lightning research and we will soon double our number of radiation sensors from 23 to about 40 or 50. With more sensors, we could greatly improve predictive models.”
Wada goes on to say that with sufficient sensor data, the team may be able to predict lightning strikes within about 10 minutes of them happening and within approximately 2 kilometres of their location.
He adds: “I’m excited to be part of this ongoing research.”
As Kanazawa has rare and ideal meteorological conditions for this kind of work, any further research is likely to be carried out in the area.
Radiation observations in storms generally come from airborne or mountain-based stations as thunderclouds are generally very high up — but winter storms in Kanazawa bring thunderclouds surprisingly close to the ground. This makes an ideal laboratory to study such events with the low-cost portable monitors — such as those developed by Wada’s research team.
These portable radiation monitors were created, in part, with technology derived from space-based satellite observatories designed for astrophysics experiments — and as such, they are quite unique.
This seems fitting, as the data from this kind of research could be extremely useful for astrophysics and solar physics researchers. Especially in the context of particle acceleration.
The research may also have another use much closer to home too.
Palaeontologists studying life from the last 50,000 years, use a technique called carbon-14 dating to determine the age of a sample. The technique relies on knowledge of the atmospheric amounts of the carbon isotopes, carbon-12 and carbon-14.
Wada explains: “It’s commonly thought carbon-14 is created by cosmic rays at a roughly constant rate, hence the predictive power of the technique.
“But there’s a suggestion thunderstorms may alter the ratio of carbon-12 to carbon-14, which may slightly change the accuracy of or calibration required for carbon-14 dating to work.”
Wada and colleagues will continue to unpick the mysteries of lightning — one of nature’s most captivating and iconic phenomena. An upcoming collaborative project based in France will launch a dedicated satellite for worldwide lightning observations from space.
Original research: http://dx.doi.org/10.1038/s42005-019-0168-y