Record energies force new thoughts on lightning
Thor, the legendary Norse God of thunder, might have much more frightening superpowers than any ancient Europeans ever imagined. In recent years, physicists using modern spacecraft have observed storms all over the planet and discovered that lightning can generate energies far in excess of what was previously thought possible. What's even more alarming is that some of them can generate anti-matter.
Despite all the discoveries that lightning researchers have made between Ben Franklin's famous kite flying and now, this familiar phenomena is still not well understood. (On a side note, as the Mythbusters have showed http://mythbustersresults.com/episode48, if Franklin had used a kite on a string to attract a lightning bolt, he would probably have been killed and never been a founding father).
To help explain lightning, scientists have recently taken two satellites designed for astronomy and turned their gaze instead towards our own planet, using the advanced instruments on board to study lighting storm clouds from far above. The two spacecraft are called FERMI (operated by NASA) and AGILE (operated by the Italian Space Agency), and each of them have added major pieces to the puzzle while forcing a rethinking of modern day lightning science.
The Italian AGILE satellite orbits above the equator and logs flashes of gamma rays from earthly thunderstorms and cosmic sources.
Physicists have known for nearly two decades that thunderstorms can produce massive bursts of gamma rays called Terrestrial Gamma Ray Flares (TGFs). But in the past, spacecraft had been limited in how high of energies they could detect. Despite orbiting hundreds of miles above Earth, the AGILE spacecraft recently shattered old notions what it meant to have a high-energy thunderstorm. The satellite has now recorded energies five times higher than had ever been seen associated with lightning before.
Most pilots avoid flying through thunderstorms, but it's now worried that if you were flying past one of these storms in an airplane, you could be exposed to dangerous radiation. In fact, scientists say that the energy some lightning can produce would be impressive if it were coming from an eruption on the surface of the sun.
What makes the mystery even greater is that lightning strikes millions of times every day, but only a very small fraction of those storms can produce TGFs. It's unclear to physicists how certain storms can create them when others don't at all.
Recently, another major discovery was also made by NASA's FERMI spacecraft. Scientists used the orbiter to glimpse large amounts of anti-matter erupting from lightning storms. Like AGILE, the spacecraft measured incredible energies, but its detectors also indicated that the gamma rays were colliding with positrons, which are their anti-matter counterparts.
Observation of positrons from a terrestrial gamma ray flash by the Fermi gamma ray telescope.
Before these discoveries, physicists had thought they were on the right track towards finally creating a model to explain lightning. It's hoped that the new data can be worked into old models, but if they can't find a way to incorporate the results, they'll have to go back to the drawing board to create entirely new models.
Whatever the final result, this mystery will most likely need to be solved in a lab and not in a real cloud. As Ben Franklin could tell us, it's incredibly hard to measure lightning. Determining a potential difference – or voltage – requires taking a measurement at two different places, and it's hard enough to convince one pilot to fly through a thunderstorm cloud, but it's that much harder to convince two to do it. Especially if you tell them you expect it to generate several hundred million volts of electricity.
For more information:
Recent PRL viewpoint
Scientific American piece on how cosmic rays might play a role in lightning.
And a great time lapse image from the kind folks at NASA.