Editor’s Note: Don Lincoln is a senior scientist at the Fermi National Accelerator Laboratory. He is the author of “The Large Hadron Collider: The Extraordinary Story of the Higgs Boson and Other Stuff That Will Blow Your Mind.” He also produces a series of science education videos. Follow him on Facebook. The opinions expressed in this commentary are solely his. View more opinion articles on CNN.
Advances in science are often the result of combining ideas and information from scientific disciplines that seem to be otherwise unrelated. A familiar example might be how scientists came to understand the double helix of DNA, which required mixing biology and x-ray crystallography.
And now, a new scientific duo will allow us to study one of the most fascinating phenomena in the Earth’s atmosphere: lightning storms. Radiation from space and meteorology have revealed that the electricity of lightning storms can be far more powerful than anyone ever expected.
With the ability to generate as much power as a modern nuclear power plant, lightning storms are a glorious display of the power of nature, which have awed humanity for millennia. Whether they were thought to be Thor fighting the Frost Giants or understood using the more modern idea of electricity, voltages and electric fields, it is hard to compete with a wave of lightning rolling across the sky, accompanied by a cacophonous rumble of thunder.
Meteorologists have long studied what produces a thundercloud. Friction between water droplets and air separate electric charges into positive and negative, with one set rising to the top of the clouds and others descending to the bottom. This separation of charges results in huge electric potential, such that air, which is normally an insulator, becomes a conductor and the clouds discharge, emitting a thunderous stroke of light and sound.
By sending airplanes and weather balloons into the center of lightning storms, scientists were able to measure just how large the voltages can be in thunderclouds, with the largest value reaching 130 million volts. That record stood for a long time – until now.
A new technique for studying the inside of a lightning storm has been developed that exploits radiation from space to peer inside an entire thunderstorm and measure all of the voltages in the storm, rather than just those in a few clouds.
You might not know it, but the entire Earth is under assault. A constant barrage of particles called cosmic rays hits the Earth’s atmosphere. Cosmic rays are usually just protons boiled off from the Sun, which hit atoms in the Earth’s atmosphere. These collisions smash apart the atoms’ nuclei and the result are many particles – one proton in and many out. This is due to Einstein’s theory of relativity.
The energy of these highly energetic cosmic rays converts into an array of subatomic particles. Those particles go on and hit other atoms in the atmosphere, making even more particles. Eventually they decay, and what filters down to the Earth’s surface is a steady rain of an unstable subatomic particle called a muon.
In addition to being created in cosmic ray collisions, muons can also be made in particle accelerators. They are much like the more familiar electron. Most importantly, they have an electrical charge, which can be affected by electrical fields like the ones that exist in thunderstorms. Because we can measure cosmic rays both on a clear day and during a thunderstorm, we can use these two different conditions to gauge the electric fields inside the storm.
The GRAPES-3 experiment is located in India and was built to study the properties of muons originating from cosmic rays. It is an array of 400 muon detectors, spread over 25,000 square meters (6.2 acres).
The GRAPES-3 experimenters noticed that when a thunderstorm passed over their detector, the number of muons they observed got smaller compared to the rate before the thunderstorm arrived. The very strong electric fields inside the storm can deflect the muons so they entirely miss the detector – that was the reason the muon rate dropped. The effect was very small (rarely did they observe a change of more than 0.4%), but the detector is sophisticated enough to measure that accurately.
They set out to study this in more detail, first by adding electric field measuring devices around the perimeter of their detector. Then they waited.
Over three and a half years, from April 2011 to December 2014, they observed 184 thunderstorms, with seven of them being big enough to alter their detected rate of muons by a large amount.
For six of those seven storms, the electric field measuring devices indicated a very complicated electrical situation, which was hard to characterize properly. But a storm that occurred on December 1, 2014 was both big enough and simple enough for the scientists to simulate.
What they found astonished them. In this monster storm, their calculations indicated that the voltage in the storm was 1.3 billion volts, about ten times more than the biggest voltage measured previously. This equates to more than two billion watts of power, which is comparable to a large and modern nuclear or hydroelectric plant.
Such an enormous voltage, while very surprising, was a welcome result, as it answered some key questions. For instance, scientists have long known that powerful equatorial thunderstorms can generate gamma rays, which is a kind of nuclear radiation. How they did so was a mystery – it is impossible for storms harboring 130 million volts of electrical potential to make the observed gamma rays. But with voltages of 1.3 billion volts, gamma rays are easily explainable.
The incredible magnitude of the voltage, compared to prior measurements, can be explained by the fact that the weather balloons and airplanes, previously used sample only a small part of the storm. Using cosmic ray muons, scientists are able to study the entire storm at one time.
So, with any such scientific announcement, the most important question to ask is, “Is this a reliable measurement?” In this case, some caution is warranted. The study presenting these extraordinary findings will be published in the journal Physical Review Letters, which is one of the most prestigious scientific journals of its kind, and it has undergone stringent peer review. On the other hand, the measurement reports only a single thunderstorm, and the specific model used in the theoretical calculation was a simple one. It’s clear that a more refined model could give a different result.
Still, the technique is fascinating. Even if a more refined study results in a different numerical value for the electrical potential inside the storm, it is quite likely that the approach of using cosmic ray muons to study thunderstorms will continue to be developed.
Science is often the most fascinating and productive when techniques from different disciplines are combined. Cross-disciplinary studies have often revolutionized our understanding our understanding of perplexing scientific mysteries. It could well be that cosmic rays and thunderstorms will similarly shake up what we thought we knew about one of nature’s most majestic spectacles.