PREVIEW

Swiss researchers have recorded X-rays being produced by upward positive lightning flashes for the first time ever. The observation gives important insight into the origins of this rare form of lightning. Globally, lightning is responsible for over 4,000 fatalities and billions of dollars in damage every year. Understanding exactly how lightning forms is key for reducing risk, but because lightning occurs on sub-millisecond timescales, direct measurements are extremely difficult to obtain. Researchers have for the first time directly measured an elusive phenomenon that explains a lot about the birth of a lightning bolt: X-ray radiation. They recorded lightning strikes at the Säntis tower in northeastern Switzerland, identifying X-rays associated with the beginning of upward positive flashes. Although X-ray emissions have previously been observed from other types of lightning, this is the first time they have been captured from upward positive flashes. The association of X-rays with a very rapid electric field changes supported the theory that sudden increases in the air’s electric field causes ambient electrons to “run away” and become a plasma, causing lightning. The Säntis tower offers unique and ideal measurement conditions. The 124-metre tower is perched atop a high peak of the Appenzell Alps, making it a prime lightning target.