A research team led by Penn State University (USA) has just published a detailed answer to one of the oldest questions in meteorology: What actually triggers lightning to form in thunderstorm clouds?
In a paper published in the Journal of Geophysical Research on July 28, Professor Victor Pasko's team presented the first quantitative model that accurately describes how strong electric fields in thunderclouds can initiate a chain reaction that produces lightning.
The mechanism begins when electrons - which are "seeded" by cosmic rays from outer space - are accelerated by electric fields in the clouds.
When electrons collide with gas molecules like nitrogen and oxygen, they produce X-rays and high-energy photons, which in turn trigger "electron avalanches" - a chain reaction that leads to lightning.
“Our discovery is the first physically and quantitatively sound explanation for the natural process of lightning initiation,” said Pasko. “It connects X-ray phenomena, electric fields and electron acceleration.”
To demonstrate the model, the team combined mathematical simulations with field data collected from NASA high-altitude reconnaissance aircraft, satellites, and ground-based sensors. This allowed them to explain phenomena such as terrestrial gamma-ray flashes (TGFs), which are brief, invisible bursts of X-rays that occur in thunderstorms without obvious flashing lights or radio waves.
"We have identified the conditions in the cloud that are necessary for the chain reaction to occur and clarified why diverse radio signals are sometimes observed before lightning strikes," said Zaid Pervez, a PhD student in the team.
The special feature of the model is the ability to simulate very small regions inside the cloud - where the initial reaction takes place. According to Mr. Pasko, it is this narrow concentration of energy, combined with the large variability of the reaction intensity, that causes some gamma rays to appear that are invisible to the naked eye and undetectable by radio wave devices.
In addition to Penn State, the project involved experts from France, the Czech Republic, Denmark and NASA.
The model, called "Photoelectric Feedback Discharge" and the entire equation, has been made public for the scientific community to use and verify./.
Source: https://www.vietnamplus.vn/dieu-gi-thuc-su-kich-hoat-tia-set-hinh-thanh-trong-cac-dam-may-dong-post1053405.vnp
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