Convective storms hold an extraordinary
surprise. Under just the right conditions,
they fire off some of the highest-energy light naturally found on Earth--
terrestrial gamma-ray flashes, or TGFs.
Rising and falling snow and ice particles
repeatedly collide, filling the cloud with electrical charge. Once the
electric field is strong enough, a current flows and a lightning flash
occurs. The flash produces an abrupt reconfiguration of
the electric field. In some cases, a surge of electrons
rushes toward the upper part of the storm at speeds nearly as
fast as light. When deflected by air molecules, these
accelerated electrons give off gamma rays, producing a TGF.
Data from NASA's Fermi Gamma-ray Space Telescope
suggest more than a thousand TGFs occur each day all over the globe.
For the first time, improved data link dozens of
TGFs to specific tropical weather systems.
Tropical storms far from land tend to generate less frequent lightning.
Nevertheless, observations show they are surprisingly prolific producers
of TGFs. Tropical Storm Manuel
made landfall just shy of hurricane strength. As it rapidly
weakened, it produced two TGFs within 24 hours.
More typically, TGFs are associated with the strengthening
phase of a storm. As Typhoon Bolaven rapidly
developed in 2012, thunderstorms nearly 500 miles from
its center launched a TGF with four distinct pulses.
So far, the record-holder for TGFs
is the rapidly strengthening tropical wave that later gave birth
to Hurricane Julio. It produced four TGFs within
100 minutes. A fifth followed the next day. with nothing further.
What scientists learned so far
is that weather tropical storms are capable of producing more TGFs,
and those events can arise anywhere in the storm.
For stronger storms, like hurricanes and typhoons, TGFs are more common
in the outer rain bands, which host the highest lightning flash rates
in these storms. The findings provide new insights
into the relationship between storm intensity, lightning frequency,
and TGFs. This adds another important piece to the puzzle
of our understanding of TGFs and how they are created in thunderstorms--
the most powerful natural particle accelerators on planet Earth.
On-screen text: NASA astrophysics
[Beeping]