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Why do researchers discover lightning branches and flicker

Publicado em 24 abril 2021

Analysis of the first ultra-slow motion recording of the upward flash suggests a possible explanation for the formation of luminescent structures after the discharge splits in the atmosphere.

Researchers at the National Institute for Space Research (INPE) have collaborated with colleagues in the United States, United Kingdom and South Africa to record for the first time the formation and divergence of lightning structures due to lightning strikes.

Analysis of images taken with a super slow-motion camera revealed why lightning strikes can split into two parts, forming a luminescent structure that is perceived by the human eye as flickering.

This study was supported by FAPESP.An article outlining the results is published in Science report..

“We were able to get the first optical observations of these phenomena and find a possible explanation for divergence and flicker,” project lead researcher Marcelo Magalya Esfares Saba told Agência FAPESP. Told. Saba is a researcher at INPE’s Atmospheric Electricity Group (ELAT).

Researchers used ultra-fast digital video cameras to flash more than 200 times during the summer thunderstorms in São Paulo (Brazil) and Rapid City, South Dakota (USA) between 2008 and 2019. I recorded it. Skyscrapers or other above-ground structures that propagate upward to the clouds above.

The upward flash they recorded was caused by a lightning discharge from a positively charged cloud to the ground. This is much more common, as explained by the same INPE research group. Previous research..

“Upward lightning strikes at the top of a tower or at a lightning rod in a skyscraper, for example, when the storm’s electric field is blocked by a cloud-to-ground discharge 60 km away,” says Saba.

The study conditions were very similar in Brazil and the United States, but the luminescent structure was observed only with three upward flashes recorded in the United States. These were formed by a positive leader discharge propagating towards the cloud base.

“The advantage of recording an image of an upward lightning bolt is that you can see the entire orbit of these positive leaders from the ground to the cloud base. Once in the clouds, they disappear,” Saba said. Said.

Researchers have discovered that a low-intensity discharge with a paintbrush-like structure can form at the tip of a positive reader. “We have observed that this discharge, often referred to as the corona brush, can change direction, split in two, and define the path of lightning strikes and their branches,” says Saba.

If the upward flash branches successfully, it may go left or right. If the branch fails, the corona brush can produce very short segments that are as bright as the reader itself. These segments first appear a few milliseconds after the corona brush is split and pulsate as the leader propagates upwards toward the cloud base.

“Flickers are repeating unsuccessful attempts to initiate a branch,” says Saba, and flicker may explain why multiple lightning discharges occur so often, but it tests this theory. Needs further research.

Reference: “Optical observation of upward lightning needles” by Marcelo midfielder Saba, Amanda R. Depaiba, Luke C. Concorato, Tom A. Warner, and Karina Schumann, October 15, 2020. Science report..
DOI: 10.1038 / s41598-020-74597-6 Why do researchers discover lightning branches and flicker