Fermi Improves Its Vision For Thunderstorm Gamma-ray Flashes

Storm clouds produce some of the highest-energy light naturally made on Earth: terrestrial gamma-ray flashes (TGFs). Using data from NASA's Fermi Gamma-ray Space Telescope and ground-based lightning detection networks, scientists tracking these fleeting outbursts are beginning to learn more about how conditions in hurricanes, typhoons and other tropical weather systems set the stage for TGFs. Credit: NASA's Goddard Space Flight CenterMusic: Glacial Fields and The Piper from Killer Tracks.Watch this video on the NASA Goddard YouTube channel.Complete transcript available. Hurricane Manuel launched a TGF on Sept. 15, 2013, shortly after it made landfall in the Mexican state of Michoacán (lower inset image). Manuel fired off a second TGF the following day. The magenta symbols mark the TGF locations on satellite images of the storm. Credit NASA’s Goddard Space Flight Center During a period of rapid strengthening on Aug. 23, 2012, Typhoon Bolaven launched its only TGF from an outer rain band located nearly 490 miles (785 km) from the storm's center (roughly bottom center of the full image). The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image of Bolaven the following day. Credit: NASA Goddard Space Flight Center/Jeff Schmaltz, LANCE MODIS Rapid Response Team About a thousand times a day, thunderstorms fire off fleeting bursts of some of the highest-energy light naturally found on Earth. These events, called terrestrial gamma-ray flashes (TGFs), last less than a millisecond and produce gamma rays with tens of millions of times the energy of visible light. Since its launch in 2008, NASA's Fermi Gamma-ray Space Telescope has recorded more than 4,000 TGFs, which scientists are studying to better understand how the phenomenon relates to lightning activity, storm strength and the life cycle of storms.Now, for the first time, a team of NASA scientists has analyzed dozens of TGFs launched by the largest and strongest weather systems on the planet: tropical storms, hurricanes and typhoons. Scientists suspect TGFs arise from the strong electric fields near the tops of thunderstorms. Under certain conditions, these fields become strong enough to drive an "avalanche" of electrons upward at nearly the speed of light. When these accelerated electrons race past air molecules, their paths become deflected slightly. This change causes the electrons to emit gamma rays. The team studied 37 TGFs associated with, among other storms, typhoons Nangka (2015) and Bolaven (2012), Hurricane Paula (2010), the 2013 tropical storms Sonia and Emang and Hurricane Manuel, and the disturbance that would later become Hurricane Julio in 2014. What the scientists have learned so far is that TGFs from tropical systems do not have properties measurably different from other TGFs detected by Fermi. Weaker storms are capable of producing greater numbers of TGFs, which may arise anywhere in the storm. In more developed systems, like hurricanes and typhoons, TGFs are more common in the outermost rain bands, areas that also host the highest lightning rates in these storms.Most of the tropical storm TGFs occurred as the systems intensified. Strengthening updrafts drive clouds higher into the atmosphere where they can generate powerful electric fields, setting the stage for intense lightning and for the electron avalanches thought to produce TGFs. For More InformationSee [https://www.nasa.gov/feature/goddard/2017/nasas-fermi-catches-gamma-ray-flashes-from-tropical-storms/](https://www.nasa.gov/feature/goddard/2017/nasas-fermi-catches-gamma-ray-flashes-from-tropical-storms/) Related pages

New research merging Fermi data with information from ground-based radar and lightning networks shows that terrestrial gamma-ray flashes arise from an unexpected diversity of storms and may be more common than currently thought. Watch this video on the NASA Goddard YouTube channel. For complete transcript, click here. Updrafts and downdrafts within thunderstorms force rain, snow and ice to collide and acquire an electrical charge. Usually, positive charge accumulates in the upper part of the storm and negative charge gathers below. When this electrical field becomes so strong it breaks down the insulating properties of air, a lightning discharge occurs. Under just the right conditions, the upper part of an intracloud lightning bolt disrupts the storm's electric field in such a way that an avalanche of electrons surges upward at high speed. When these fast-moving electrons are deflected by air molecules, they emit gamma rays and create a TGF. There are about 2,000 intracloud discharges for each TGF detected by Fermi.Credit: NASA's Goddard Space Flight Center Three storms within the coverage area of the NEXRAD radar site at Key West, Florida, illustrate the range of weather capable of producing TGFs. The insets show the maximum height of radar reflectivity echoes, which helps identify strong thunderstorm updrafts, for each storm at the time a TGF occurred. The central column shows the 3-D distribution of the radar echoes and the location of the TGF (shown as a lightning bolt).Credit: NASA's Goddard Space Flight Center/T. Chronis and M. Briggs, UAH Merging data on high-energy bursts seen on Earth by NASA's Fermi Gamma-ray Space Telescope with data from ground-based radar and lightning detectors, scientists have completed the most detailed analysis to date of the types of thunderstorms producing terrestrial gamma-ray flashes, or TGFs. TGFs occur unpredictably and fleetingly, with durations less than a thousandth of a second, and remain poorly understood. Yet the gamma rays they produce rank among the highest-energy light naturally produced on Earth.Earlier Fermi studies helped uncover lightning-like radio signals emitted by TGFs. This made it possible to use ground-based lightning location networks to pin down storms producing the flashes, opening the door to a deeper understanding of the meteorology powering these extreme events. Scientists gathered a sample of nearly 900 Fermi TGFs accurately located by ground networks, which can pinpoint the location of lightning discharges -- and the corresponding signals from TGFs -- to within 6 miles (10 km) anywhere on the globe. From this group, they identified 24 TGFs that occurred within areas covered by Next Generation Weather Radar (NEXRAD) sites. The researchers found that even weak and marginally electrified storms are capable of producing TGFs. The new study also confirms previous findings indicating that TGFs tend to occur near the highest parts of a thunderstorm, between about 7 and 9 miles (11 to 14 kilometers) high. However, TGFs associated with lightning at lower altitudes would be so weakened by traveling a longer path through the atmosphere that Fermi couldn't detect them. If true, the estimated number of 1,100 TGFs occurring each day may be much larger than previously thought. For More InformationSee [http://www.nasa.gov/content/goddard/nasas-fermi-mission-brings-deeper-focus-to-thunderstorm-gamma-rays/](http://www.nasa.gov/content/goddard/nasas-fermi-mission-brings-deeper-focus-to-thunderstorm-gamma-rays/) Related pages

TGFs produce high-energy electrons and positrons. Moving near the speed of light, these particles travel into space along Earth's magnetic field.Watch this video on the NASAexplorer YouTube channel.For complete transcript, click here. Interactions with matter can produce gamma rays and vice versa. So-called "bremsstrahlung" gamma rays result when high-energy electrons traveling close to the speed of light become deflected by passing near an atom or molecule. In pair production, a gamma ray passing through the electron shell of an atom transforms into two particles: an electron and its antimatter opposite, a positron. Animated diagram showing the behavior and composition of TGF emissions.Credit: NASA/Goddard Space Flight Center/J. Dwyer/Florida Inst. of Technology A TGF produces gamma rays (magenta) as well as high-energy electrons (yellow) and positrons (green). This simulation tracks a TGF and its particle beams from their origin altitude of 9.3 miles (15 km) to 373 miles (600 km), beyond Fermi's orbit. Credit: Joe Dwyer/Florida Inst. of Technology Sidebar: How thunderstorms launch particle beams into space On Dec. 14, 2009, while NASA's Fermi flew over Egypt, the spacecraft intercepted a particle beam from a terrestrial gamma-ray flash (TGF) that occurred over its horizon. Fermi's Gamma-ray Burst Monitor detected the signal of positrons annihilating on the spacecraft — not once, but twice. After passing Fermi, some of the particles reflected off of a magnetic "mirror" point and returned. On Dec. 14, 2009, while NASA's Fermi flew over Egypt, the spacecraft intercepted a particle beam from a terrestrial gamma-ray flash (TGF) that occurred over its horizon. Fermi's Gamma-ray Burst Monitor detected the signal of positrons annihilating on the spacecraft — not once, but twice. After passing Fermi, some of the particles reflected off of a magnetic "mirror" point and returned. No Labels. Fermi's position relative to the TGF it detected. Artist interpretation of the cloud of electrons and positrons passing through the Fermi satellite and causing it to emit gamma rays. Artist interpretation of electrons accelerating upwards from a thunderhead. Map of all terrestrial gamma-ray flashes detected by Fermi's Gamma-ray Burst Monitor through the end of 2010.For animated version, go here, This image from the Meteosat 9 weather satellite was taken on Dec. 14, 2009, about 7 minutes after Fermi detected positrons from a TGF. No storms are present over Egypt, where Fermi was located at the time of the event, but thunderstorms are plentiful over Zambia. Credit: SSEC/Univ. of Wisconsin, Madison NASA's Fermi Gamma-ray Space Telescope has detected beams of antimatter launched by thunderstorms. Acting like enormous particle accelerators, the storms can emit gamma-ray flashes, called TGFs, and high-energy electrons and positrons. Scientists now think that most TGFs produce particle beams and antimatter.For additional animations showing bremsstrahlung and pair production gamma ray reactions, go here.For more visualizations showing Fermi's TGF detections, go to#3747, #3748, and #3756.For animations of the Fermi spacecraft and matter/antimatter, go to#10707 and #10651. For More InformationSee [http://www.nasa.gov/mission_pages/GLAST/news/fermi-thunderstorms.html](http://www.nasa.gov/mission_pages/GLAST/news/fermi-thunderstorms.html) Related pages