1 00:00:13,060 --> 00:00:09,020 Thunder claps 2 00:00:13,080 --> 00:00:17,100 of times every second. Most of these electrical flashes remain in the clouds, 3 00:00:17,120 --> 00:00:21,190 with only about a fifth of them reaching low enough to strike trees, buildings 4 00:00:21,210 --> 00:00:25,220 or the ground. Yet lightning bolts in the clouds deliver a unique and 5 00:00:25,240 --> 00:00:29,260 powerful punch of their own. They're directly linked to events that produce some of the 6 00:00:29,280 --> 00:00:33,290 highest-energy radiation naturally found on Earth: terrestrial gamma-ray 7 00:00:33,310 --> 00:00:37,350 flashes, or TGFs for short. 8 00:00:37,370 --> 00:00:41,460 Thanks to recent work by NASA's Fermi Gamma-ray Space Telescope, 9 00:00:41,480 --> 00:00:45,560 scientists have come a few steps closer to understanding these extraordinary outbursts. 10 00:00:45,580 --> 00:00:49,620 When lightning flashes high in the clouds, its energy may alter the strong 11 00:00:49,640 --> 00:00:53,670 electric fields near the top of the storm. About a thousand times each 12 00:00:53,690 --> 00:00:57,760 day, this sudden change triggers an upward surge of high-speed electrons. 13 00:00:57,780 --> 00:01:01,790 Reaching speeds nearly as fast as light, these accelerated electrons give 14 00:01:01,810 --> 00:01:05,820 off gamma rays when they're deflected by air molecules. 15 00:01:05,840 --> 00:01:09,850 TGFs happen quickly and randomly, so even catching them by satellite has 16 00:01:09,870 --> 00:01:13,900 been difficult. But new results from the Gamma-ray Burst Monitor on Fermi 17 00:01:13,920 --> 00:01:17,940 are giving scientists fresh insights. Last year 18 00:01:17,960 --> 00:01:21,980 the GBM team showed that TGFs well away from Fermi produced beams of 19 00:01:22,000 --> 00:01:26,020 charged particles that could travel along Earth's magnetic field and hit the satellite. 20 00:01:26,040 --> 00:01:30,080 Now, thanks to advancements in data processing, Fermi's GBM 21 00:01:30,100 --> 00:01:34,140 is better at detecting TGFs than ever before. As a result, 22 00:01:34,160 --> 00:01:38,260 scientists have discovered that radio signals once thought to be produced by the lightning that 23 00:01:38,280 --> 00:01:42,370 triggers a TGF are in fact broadcast by TGFs themselves. 24 00:01:42,390 --> 00:01:46,400 Each lightning stroke creates a burst of Very Low 25 00:01:46,420 --> 00:01:50,430 Frequency radio waves. Through the World Wide Lightning Location Network, 26 00:01:50,450 --> 00:01:54,470 scientists use this unique radio signal to track electrical activity around the globe. 27 00:01:54,490 --> 00:01:58,500 For some time, scientists have know that TGFs were associated with 28 00:01:58,520 --> 00:02:02,530 strong radio signals, so it was natural to think that these radio signals were 29 00:02:02,550 --> 00:02:06,560 produced by the lightning stroke that triggered the TGFs. Here's one 30 00:02:06,580 --> 00:02:10,590 instance that highlights why the GBM team now questions this interpretation. 31 00:02:10,610 --> 00:02:14,610 It's August 2009 and Fermi is flying over thunderstorms 32 00:02:14,630 --> 00:02:18,620 off Mexico's West Coast. Each symbol marks the location of a lightning 33 00:02:18,640 --> 00:02:22,630 The highlighted circle shows how much of 34 00:02:22,650 --> 00:02:26,650 Earth's surface Fermi can see at any given moment. Just as the satellite passes 35 00:02:26,670 --> 00:02:30,680 over the storms, a TGF occurs. There's no other lightning 36 00:02:30,700 --> 00:02:34,710 near that position when Fermi detected the TGF. 37 00:02:34,730 --> 00:02:38,750 hundreds of TGFs and comparing them to radio-based lightning locations, 38 00:02:38,770 --> 00:02:42,780 the GBM team concludes that both the gamma-ray and the the strong radio emission comes 39 00:02:42,800 --> 00:02:46,780 from the TGF. The team also finds that weaker radio bursts 40 00:02:46,800 --> 00:02:50,810 ocurring up to several thousandths of a second before or after a TGF 41 00:02:50,830 --> 00:02:54,830 actually represent the individual lightning stroke associated with it. 42 00:02:54,850 --> 00:02:58,870 The GBM findings confirm a theory published in 2011 43 00:02:58,890 --> 00:03:02,900 that the same avalanche of speedy electrons that creates a TGFs gamma 44 00:03:02,920 --> 00:03:06,920 rays also produce strong Very Low Frequency radio signals. 45 00:03:06,940 --> 00:03:10,940 With this knowledge, scientists can pair the Fermi 46 00:03:10,960 --> 00:03:14,960 TGF sample with the more precise radio positions from the World Wide Lightning 47 00:03:14,980 --> 00:03:19,020 Location Network. This will clarify weather patterns associated with TGFs 48 00:03:19,040 --> 00:03:23,080 and usher in new studies, perhaps helping scientists determine which 49 00:03:23,100 --> 00:03:27,110 types of thunderstorms produce some Earth's highest-energy natural light.