I received this one late last night after I'd gome to bed.
 
Terrestrial Gamma-ray Flashes, More Common Than Previously Thought?
 
Dec 31, 2014:  Each day, thunderstorms around the world produce about a
thousand quick bursts of gamma rays, some of the highest-energy light
naturally found on Earth. By merging records of events seen 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 involved.
 
"Remarkably, we have found that any thunderstorm can produce gamma
rays, even those that appear to be so weak a meteorologist wouldn't look
twice at them," said Themis Chronis, who led the research at the
University of Alabama in Huntsville (UAH).
 
https://www.youtube.com/watch?v=JgK4Ds_Sj6Q
 
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. Play video [Worth seeing]
 
The outbursts, called terrestrial gamma-ray flashes (TGFs), were discovered
in 1992 by NASA's Compton Gamma-Ray Observatory, which operated until 2000.
TGFs occur unpredictably and fleetingly, with durations less than a
thousandth of a second, and remain poorly understood.
 
In late 2012, Fermi scientists employed new techniques that effectively
upgraded the satellite's Gamma-ray Burst Monitor (GBM), making it 10 times
more sensitive to TGFs and allowing it to record weak events that were
overlooked before.
 
"As a result of our enhanced discovery rate, we were able to show that
most TGFs also generate strong bursts of radio waves like those produced by
lightning," said Michael Briggs, assistant director of the Center for
Space Plasma and Aeronomic Research at UAH and a member of the GBM team.
 
Previously, TGF positions could be roughly estimated based on Fermi's
location at the time of the event. The GBM can detect flashes within about
500 miles (800 kilometers), but this is too imprecise to definitively
associate a TGF with a specific storm.
 
Ground-based lightning networks use radio data to pin down strike
locations. The discovery of similar signals from TGFs meant that scientists
could use the networks to determine which storms produce gamma-ray flashes,
opening the door to a deeper understanding of the meteorology powering
these extreme events.
 
Chronis, Briggs and their colleagues sifted through 2,279 TGFs detected by
Fermi's GBM to derive a sample of nearly 900 events accurately located by
the Total Lightning Network operated by Earth Networks in Germantown,
Maryland, and the World Wide Lightning Location Network, a research
collaboration run by the University of Washington in Seattle. These systems
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, the team identified 24 TGFs that occurred within areas
covered by Next Generation Weather Radar (NEXRAD) sites in Florida,
Louisiana, Texas, Puerto Rico and Guam. For eight of these storms, the
researchers obtained additional information about atmospheric conditions
through sensor data collected by the Department of Atmospheric Science at
the University of Wyoming in Laramie.
 
"All told, this study is our best look yet at TGF-producing storms,
and it shows convincingly that storm intensity is not the key," said
Chronis, who will present the findings Wed., Dec. 17, in an invited talk at
the American Geophysical Union meeting in San Francisco. A paper describing
the research has been submitted to the Bulletin of the American
Meteorological Society.
 
Scientists suspect that TGFs arise from strong electric fields near the
tops of thunderstorms. Updrafts and downdrafts within the storms force
rain, snow and ice to collide and acquire electrical charge. Usually,
positive charge accumulates in the upper part of the storm and negative
charge accumulates below. When the storm's electrical field becomes so
strong it breaks down the insulating properties of air, a lightning
discharge occurs.
 
Under 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.
 
About 75 percent of lightning stays within the storm, and about 2,000 of
these intracloud discharges occur for each TGF Fermi detects.
 
The new study 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. "We suspect this isn't the full story,"
explained Briggs. "Lightning often occurs at lower altitudes and TGFs
probably do too, but traveling the greater depth of air weakens the gamma
rays so much the GBM can't detect them."
 
Based on current Fermi statistics, scientists estimate that some 1,100 TGFs
occur each day, but the number may be much higher if low-altitude flashes
are being missed.
 
While it is too early to draw conclusions, Chronis notes, there are a few
hints that gamma-ray flashes may prefer storm areas where updrafts have
weakened and the aging storm has become less organized. "Part of our
ongoing research is to track these storms with NEXRAD radar to determine if
we can relate TGFs to the thunderstorm life cycle," he said.
 
Credits:
Production editor: Dr. Tony Phillips | Credit: Science{at}NASA
 
More information:
 
Download video in HD formats from NASA Goddard's Scientific Visualization Studio
 
Fermi Improves its Vision for Thunderstorm Gamma-Ray Flashes (12.06.2012)
 
NASA's Fermi Catches Thunderstorms Hurling Antimatter into Space (01.10.2011)
 
 
Regards,
 
Roger

--- D'Bridge 3.99