WEBVTT FILE

1
00:00:00.010 --> 00:00:04.020
[Thunder]

2
00:00:04.040 --> 00:00:08.050
[Thunder]

3
00:00:08.070 --> 00:00:12.070
[Thunder] [Music]

4
00:00:12.090 --> 00:00:16.110
Deep within their roiling clouds, thunderstorms hold an elusive

5
00:00:16.130 --> 00:00:20.170
surprise. Under just the right conditions, they produce some of the highest

6
00:00:20.190 --> 00:00:24.250
energy radiation naturally found on Earth: terrestrial gamma-ray

7
00:00:24.270 --> 00:00:28.270
or TGFs for short.

8
00:00:28.290 --> 00:00:32.290
Studies by NASA's Fermi Gamma-ray Space Telescope

9
00:00:32.310 --> 00:00:36.320
have shown that TGFs fire up about 1,100 times a day.

10
00:00:36.340 --> 00:00:40.330
Now, new research combines Fermi detections

11
00:00:40.350 --> 00:00:44.360
with ground-based radar and lightning location data.

12
00:00:44.380 --> 00:00:48.380
These studies show that TGFs come from more diverse types of storms than previously thought

13
00:00:48.400 --> 00:00:52.410
In a thunderstorm, collisions among rain and snow cause different

14
00:00:52.430 --> 00:00:56.440
parts of the clouds to develop positive and negative electrical charges.

15
00:00:56.460 --> 00:01:00.470
When the strength of the electric field overcomes the insulating properties in

16
00:01:00.490 --> 00:01:04.480
the thundercloud, a lighting flash occurs.

17
00:01:04.500 --> 00:01:08.500
Most lightning occurs entirely within the cloud and is called an intracloud flash.

18
00:01:08.520 --> 00:01:12.530
All lightning produces a strong and sudden change in the storm's electric field,

19
00:01:12.550 --> 00:01:16.540
but the upward portion of an intracloud flash sometimes sends a surge

20
00:01:16.560 --> 00:01:20.570
of electrons rushing toward the upper part of the storm. Reaching

21
00:01:20.590 --> 00:01:24.600
speeds nearly as fast as light, these accelerated electrongs give off

22
00:01:24.620 --> 00:01:28.610
gamma rays when their paths are deflected by air molecules. Using

23
00:01:28.630 --> 00:01:32.640
global lightning location networks, scientists can determine a TGF

24
00:01:32.660 --> 00:01:36.680
position more accurately than with Fermi data alone. Two dozen

25
00:01:36.700 --> 00:01:40.690
localized TGFs occurred within areas covered by next-generation weather

26
00:01:40.710 --> 00:01:44.710
radar systems. This gives scientists the opportunity to begin studying

27
00:01:44.730 --> 00:01:48.750
the kinds of storms that produce TGFs. These slices of

28
00:01:48.770 --> 00:01:52.770
radar data capture different types of storms encompassing a wide range of

29
00:01:52.790 --> 00:01:56.780
updraft strengths. Even the weakest of them produced a TGF.

30
00:01:56.800 --> 00:02:00.830
Another finding: TGFs seem to occur

31
00:02:00.850 --> 00:02:04.840
in the same altitude range, between 7 and 9 miles high.

32
00:02:04.860 --> 00:02:08.860
Lightning can form at much lower altitudes, so there's every reason

33
00:02:08.880 --> 00:02:12.940
to think TGFs can too, but gamma-rays from TGFs occuring

34
00:02:12.960 --> 00:02:16.960
deeper in the atmosphere are greatly weekend, they're too dim for Fermi to detect,

35
00:02:16.980 --> 00:02:21.020
which probably means the satellite is undercounting them.

36
00:02:21.040 --> 00:02:25.050
TGFs may be far more common than we think. With this

37
00:02:25.070 --> 00:02:29.080
knowledge, scientists can design experiments to track storms and

38
00:02:29.100 --> 00:02:33.140
study how TGFs relate to their strength and evolution. This will give us

39
00:02:33.160 --> 00:02:37.240
an even better understanding of planet Earth's most powerful natural particle

40
00:02:37.260 --> 00:02:41.270
accelerator. [Beeping]

41
00:02:41.290 --> 00:02:45.310
[Beeping and thunder]

42
00:02:45.330 --> 00:02:49.016
[Thunder]