"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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