Lightning does actually strike in the same place twice!

A scientist at EPFL has developed a sensor that he subsequently fitted in the radio-TV tower at the top of the Säntis mountain, one of the places in Europe most affected by lightning. The goal is to better understand this phenomenon, which is still shrouded in mystery.

Carlos Romero is not easily discouraged! This doctoral student of Colombian origin, passionate about lightning, is determined to uncover some of the secrets of this phenomenon that everyone knows, but whose physical principles remain largely a mystery.

His thesis is dedicated to the design and construction of a totally innovative measuring device. Fifteen thousand components and eighteen months later, he didn’t hesitate to strap himself into a harness and to climb up 80 meters to install the device in one of the most extreme geographical locations in Switzerland. The radio-TV transmitter at the Säntis is built on a summit at 2502 meters, and culminates 120 meters higher up. “Inside the antenna, the temperatures can vary between –35°C in winter and +40°C in summer, explains Carlos Romero. We had to create a very robust device.”

The antenna, which is reminiscent of a rocket ready for take off, also features another characteristic: it attracts lightning! According to the statistics from the European body in charge of monitoring the phenomenon, it could even be the European location most often struck by lightning. An ideal location therefore to pursue the work of Swiss researcher Karl Berger, a world-renowned name in this field. The use of his observations, performed over nearly thirty years (1943-1972) in Monte San Salvatore (Ticino region), is today confronted with the same limits regarding accuracy as existed at the time. “The devices we have installed have an extremely fine resolution and scan a very large spectrum of wavelengths. They take 100 million measurements per second and generate so much data – one gigabyte for each lightning strike – that we had to design a special software capable of processing them” explains Farhad Rachidi, Professor in the Electromagnetic Compatibility group of the Power systems laboratory, at EPFL.

Another obstacle had to be overcome: the four hours’ distance separating EPFL and Säntis, as well as the restrictions governing access to this building, belonging to Swisscom. To remedy the first point, EPFL has formed a partnership with the Engineering School of the canton of Vaud (HEIG-VD), located in Yverdon-les-Bains, and the University of Bologna in order to develop, among other things, a full, remotely operated monitoring and control system. The gathering of data is completely automated, and the researchers receive an SMS every time lightning strikes.

The devices were installed at the end of May 2010. “Since then, we have been able to record 50 lightning strikes”, enthuses Farhad Rachidi. Moreover, the results promise to be even better in future, especially as a great mystery is already puzzling the research team: “We have measured seven lightning strikes with positive polarity, whereas the majority of those hitting Switzerland are normally negative”, adds the expert.

The research, which will be performed with the EPFL sensors, is sponsored by funding from the Swiss National Science Foundation, the European Union, Armasuisse and Montena EMC. In addition to helping us to better understand lightning, it will also serve other goals. “The accuracy of European statistics leaves much to be desired, and we could help them adjust their algorithms”, adds Carlos Romero. Moreover, an improved understanding of the electromagnetic disturbances produced by lightning will enable us to better protect electronic devices, a specialty of Farhad Rachidi’s laboratory. “We also want to understand why the movement of the blades of big wind turbines tends to attract lightning”, adds the latter, although he is sure that the sensor designed by his doctoral student will give his laboratory work for at least ten years.

Picture: lightning on the Leman lake. © Philippe Barraud

Author: Emmanuel Barraud

Source: EPFL