When the bolt gets close to the ground, it creates an intense electric field, which causes upward streamers that meet it midair. When lightning first develops, it generally sends a bolt called a step leader down toward the ground, branching in seemingly random directions. But most of it happens too fast for the human eye to glimpse, so researchers use high-speed cameras to spy how the lightning races between sky and Earth. There is no more iconic storm image than the brilliant white forks of lightning snaking their way across a menacing sky. (Image credit: Doug Jordan and Martin Uman/International Center for Lightning Research and Testing) Bright white strokes of lightning off to the side were displaced by wind blowing between strokes. The blue-green light in the image is from copper in the initial triggering wire being heated to the point of radiating light. The National Oceanic and Atmospheric Administration (NOAA) and NASA are building a geostationary lightning mapper, or GLM, to fly aboard the GOES-R satellite set to launch in 2015.Ī triggered lightning experiment conducted in Florida as part of an ongoing research effort to better understand how lightning forms. The satellite makes a lap around the planet every 90 minutes, giving scientists a picture of the amount and distribution of lightning worldwide. The University of Alabama scientists have also developed a satellite-based sensor that counts photons from low-Earth orbit. ![]() These sensors give scientists a pretty good view of lightning on the ground, but to get a global view, why not observe it from space? "It's literally a salad bowl - we got it from Target," Bitzer said. They protect the sensor from rain using an inverted metal dish. īitzer and his colleagues at the University of Alabama in Huntsville have developed a sensor that operates in the LF/VLF range and measures the change in electric field from a lightning discharge and converts it into a voltage. VLF arrays can detect lightning over land and oceans, where hurricanes and other storms develop. These operate in the 5-to-30 kilohertz range, and are spaced thousands of kilometers apart. The National Lightning Detection Network (NLDN), a network of more than 100 low-frequency sensing stations around the United States, is widely used by researchers and provides vital monitoring for predicting severe weather.Īt the broadest scale, very low frequency (VLF) arrays measure electromagnetic signals not just along the Earth's surface, but between the Earth and the ionosphere, the upper layer of the atmosphere that is electrically charged by solar radiation. These arrays operate in the range of hundreds of kilohertz to a few megahertz. Lightning also produces energy in the form of light, heat and atomic energy such as X-rays and gamma rays. These provide information about the energy released, in the form of electrical current in channels to ground. VHF sensors operate in the range of 10 to 100 megahertz and are spaced close togetherAbout a dozen VHF arrays exist nationwide, including at the University of Alabama in Huntsville, New Mexico Tech, and the Kennedy Space Center in Florida.īy contrast, low frequency (LF) arrays image larger-scale lightning activity, such as the long channels of electricity in cloud-to-ground and intra-cloud flashes. ![]() Very high frequency (VHF) arrays, collections of sensors that measure electromagnetic radiation, capture images of the fine branching structures of a lightning strike. "The higher the frequency you go to, the smaller the object you get to image," Cummins said. Three different systems capture lightning discharges over a range of different frequencies, which correspond to the energies being produced. One of the most critical are lightning mapping arrays, which are networks of electromagnetic sensors that home in on the fiery flashes and measure the energy they release. ![]() Lightning-sensing systems have been evolving since the time radios were developed around the turn of the 20 th century, Cummins said. "We've gotten pretty good at being able to quantify the number of cloud-to-ground discharges in a region, and we're getting better at quantifying the number and nature of intra-cloud discharges," Cummins told LiveScience. While lightning that strikes the ground poses the most direct threat to humans and infrastructure, lightning between or within clouds can provide warning of dangerous hail and tornadoes, said Kenneth Cummins, an atmospheric scientist at the University of Arizona, in Tucson. ![]() The wrath of Zeus takes two forms: cloud-to-ground lightning and intra-cloud lightning. Lightning strikes more than 250,000 people each year worldwide.
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