Scientists capture X-rays from upward positive lightning
EPFL researchers have for the first time recorded X-rays being produced at the beginning of upward positive lightning flashes; an observation that gives important insight into the origins of this rare – and particularly dangerous – form of lightning.
Globally, lightning is responsible for over 4,000 fatalities and billions of dollars in damage every year; Switzerland itself weathers up to 150,000 strikes annually. Understanding exactly how lightning forms is key for reducing risk, but because lightning phenomena occur on sub-millisecond timescales, direct measurements are extremely difficult to obtain.
Now, researchers from the Electromagnetic Compatibility Lab, led by Farhad Rachidi, in EPFL’s School of Engineering have for the first time directly measured an elusive phenomenon that explains a lot about the birth of a lightning bolt: X-ray radiation. In a collaborative study with the University of Applied Sciences of Western Switzerland and Uppsala University in Sweden, they recorded lightning strikes at the Säntis tower in northeastern Switzerland, identifying X-rays associated with the beginning of upward positive flashes. These flashes start with negatively charged tendrils (leaders) that ascend stepwise from a high-altitude object, before connecting with a thundercloud, transferring positive charge to the ground.
“At sea level, upward flashes are rare, but could become the dominant type at high altitudes. They also have the potential to be more damaging, because in an upward flash, lightning remains in contact with a structure for longer than it does during a downward flash, giving it more time to transfer electrical charge,” explains Electromagnetic Compatibility Lab PhD candidate Toma Oregel-Chaumont.
