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Meteorology

Lightning hunters

An Inpe team gets out into the open during thunder storms to film the lightning flashes in the southeast and to map their occurrences

It is said that a picture is worth a thousand words. Then what is the value of filming and photographing lightning, a phenomenon already monitored by detectors on land and even by satellite? It is worth a lot for the physicist Odim Mendes Junior, of the National Institute for Space Research (Inpe). Certain that the lens of a camera picks up details that would not be registered or would pass unnoticed among the data of the sensors, he explains “important parameters such as the trajectory, tortuosity and the divergence of a ray are not captured by the conventional instruments. Consequently, filming, even by laymen, helps to get a better understanding of the phenomenon.”

For two years now he has coordinated the Via-Lux Project, with a multi-disciplinary team, to map out lightning in the southeast, especially in the State of São Paulo, with photos and above all with images in movement. They have already brought together more than 100 hours of filming and 300 photos of lightning flashes. The major part of the material is made up of discharges that have hit the region of São José dos Campos, where Inpe is located, but as well there are registrations from the states of Minas Gerais, Goiás and Mato Grosso do Sul.

The project has made the team adopt very unusual habits. For them poor weather is good weather for their work. In the same way, when their computer, linked to a system developed within the project to monitor the weather in the southeast, shows probabilities of a storm in the surroundings, the researchers leave rapidly for one more mission as lightning hunters. Armed with a high resolution filming camera that takes more than 400 frames per second, and a conventional camera that registers 30 per second as well as a good photographic camera, they leave with a motto, running behind the rays to register them and then run from them to escape the discharges. “Once I got to within 8 meters of where the lightning hit, but I have never been injured”, says the coordinator.

Once the lightning flash has been documented with the camera, the hunter takes out a piece of equipment from the GPS (Global Positioning System) and notes the geographical coordinates of the location, so asto know precisely where it fell. “In this manner,” he explains “we can verify how the discharge detection systems register the filmed event, as we intend to contribute as well to a new understanding of the important systems now in operation.”

In some cases, trekking after the lightning can result in less than 2 seconds of useful filming. However, passed through the computer and dealt with frame by frame, the film can render a rich sequence of images. In one such situation in São José, at 7:18 PM on the 4th of January, it was noted that the lightning flash produced ten distinct discharges, something very unusual. The first two were extremely fast (less than 17 milliseconds) and took almost the same vertical path from the cloud to the ground. However, the third was very different, beginning with its life span of 238 milliseconds, 14 times more than its predecessors. Also its ionization channel, the path of the ray, was more inclined and tortuous, different from those before and with another peculiarity, before hitting the ground, it became visibly vertical. This indicates that the place where it hit must be a good conductor of electricity. The other discharges repeated the track of the third, through they lasted less.

But what type of information about this tortuous thin thread of light that one sees going on and off two or three times, remains registered in the sensors that monitor the skies of the country? There should be a registration for this ray, since the southeast is the only region entirely covered by a regular system of sensors. This registration should have some characteristic such as intensity, polarity and electrical discharge, whether positive, negative or bipolar, number of discharges produced (in this case ten) and the approximate location where it fell. However, the exact reconstruction of the pathway, from the cloud to the ground, as well as the spotting of unusual situations can only be carried out through images such as those obtained through the project.

Database
As well as producing, and obtaining from third parties, images of the rays, the team developed software, the ThoR-SLA, to organize large amounts of data on lightning flashes, classified through various parameters. This will permit, among other things, the automation of reports. Though still not concluded, the ThoR has already provided results. It verified that in lightning flashes with various discharges, the size of the second could be larger than that of the first. “It is an important piece of data for safety systems projects.

From this noted piece of information, we can more frequently expect a stronger second discharge falling on a piece of equipment or installation whose protection must be prepared to receive it”, says the researcher. Another module of the program allows for a simulation of the pathway and the behavior of the electrical discharges. The result of the simulation and the pathways of a filmed discharge can be seen in the images obtained.

Brazilian mystery
Nevertheless, lightning flashes are still enveloped in mystery. In Brazil, the uncertainties are greater, but there are plenty of reasons for having an interest in this theme. The size and the position of the country favor phenomena that generate storms and in which there is a large amount of electrical atmospheric activity, only regularly covered by sensors in the Southeast and in parts of the South and more Central West. Another complicating factor are the satellites that could track the lightning remain “blind” on passing over the Southeast and surroundings due to the interference of the so called South Atlantic Magnetic Anomaly.

“The satellites also have another problem. They register the total quantity of lightning flashes produced without making a distinction between those that remain in the air and those that reach the surface of the planet”, emphasizes the researcher Dr. Osmar Pinto Junior, a colleague of Dr. Mendes at Inpe and the author of a study on the rays that fell in the State during last summer.

The Project
Observational Analysis and Number Modeling of Lightning in the Southeastof Brazil (Via-Lux Project) (nº 98/03860-9); Modality Regular line of research assistance; Coordinator Dr. Odim Mendes Junior – National Institute of Spatial Research (Inpe); Investment R$ 12,860.00 and US$ 49,647.00

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