An international research team led by the University of Groningen utilized a LOFAR radio telescope to study the growth of lightning flashes in remarkable detail, proving wrong the popular belief which states that the lightning strikes once. Accordingly, lightning strikes twice, and scientists found out why.
The study shows that the negative charges created inside a thundercloud are not released in just one flash, but are partially kept alongside the leader channel at Interruptions. This happens inside constructions that the scientists have called needles. A negative charge may be the agent of a repeated discharge on the ground through these structures.
Scientists used LOFAR to study lightning
Dr. Brian Hare, professor of physics at the KVI-CART Institute of the University of Groningen said that the reason why needles have never glanced before is because of the “supreme capabilities” of LOFAR. These structures can have a length of 100 meters and a diameter of just less than five meters and are apparently too small and with life too short to be detected by other lightning detection systems.
Low-Frequency Array (LOFAR) is a Dutch radio telescope which contains thousands of simple antennas spanned all over Northern Europe. These antennas can function as a single organism because they are connected with a central computer through fiber-optic cables. Although LOFAR was developed for astronomy observations, it can also be used in lightning research due to its frequency range of antennas.
How lightning forms inside clouds
Lightning occurs when powerful updrafts produce a sort of static electricity in large cumulonimbus clouds. Segments of the cloud become charged positively and the others negatively, and when this partition is large enough, a severe discharge happens, namely the lightning. The discharge mentioned above begins with a plasma, a small area of ionized air which is hot enough to be electrically conductive. The area develops into an angled plasma channel that can expand to several kilometers.
The positive edges of the plasma gather negative charges from the cloud, which travel through the channel to the negative tip where the charge is fired.
Lightning strikes twice
Researchers have designed and created a new algorithm for LOFAR data, which enables them to watch the VHF radio emissions from two lightning flashes. The antenna pattern and the exact timestamp on all the information grant them to locate the emission sources with extremely detailed resolution.
At the place where needles are formed, there can be seen a development of a break in the discharge channel. What caused the break is the decline of changes in the channel.
Because of the repeated discharges on the side channels which were previously formed (the needles), there come the VHF emissions along the positive channel, Olaf Scholten, professor of physics at the KVI-CART institute of the University of Groningen had declared. The results of the study were published in the science journal Nature on April 18th.