David M. Smith talks with
ScienceWatch.com and answers a few questions about
this month's Emerging Research Front Paper in the field of
Article: Terrestrial gamma-ray flashes observed up
to 20 MeV
Authors: Smith, DM;Lopez, LI;Lin, RP;Barrington-Leigh,
Journal: SCIENCE, 307 (5712): 1085-1088 FEB 18 2005
Addresses: Univ Calif Santa Cruz, Dept Phys, 1156 High St,
Santa Cruz, CA 95064 USA.
Univ Calif Santa Cruz, Dept Phys, Santa Cruz, CA 95064
Univ Calif Santa Cruz, Santa Cruz Inst Particle Phys, Santa
Cruz, CA 95064 USA.
(addresses have been truncated.)
Why do you think your paper is highly
We were only the second group to observe this phenomenon (flashes of
gamma-rays associated with lightning) and we found several things that the
previous mission (NASA's Compton Gamma-ray Observatory) couldn't see.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
"We are looking carefully into the
radiation dose that could be received by
someone in an airplane above a
The new things we discovered about terrestrial gamma-ray flashes (TGFs)
were 1) the extremely high energies to which electrons are accelerated
(over 20 MeV, or nearly a thousand times higher in energy than the x-rays
used for medical imaging) and 2) the frequency with which they occur;
they're not as rare as one might have concluded from the early data.
Would you summarize the significance of your paper in
Earth's atmosphere is capable of accelerating particles to high energies in
a way normally associated with more violent environments, like solar flares
and the vicinity of black holes. These events might be the triggering
process for lightning, which, surprisingly, is not known.
How did you become involved in this research and were
any particular problems encountered along the way?
We were looking for novel uses of the data from the Reuven Ramaty High
Energy Solar Spectroscopic Imager (RHESSI) satellite, which was designed to
look for solar flares. Because of the limitations of the previous data on
TGFs, we mistakenly assumed that they would be rare and difficult to see. I
assigned the project to an undergraduate student,
Liliana Lopez, and was amazed at the brightness,
energy, and frequency of the events she eventually found. She ended up
unexpectedly the star of a summer school in this discipline that I sent
her to about the time she found the first TGFs in the RHESSI data.
Where do you see your research leading in the
We are working toward detecting these flashes at the altitudes where they
are formed (the tops of thunderstorms) instead of from a great distance
away, in space. Instead of seeing about 20-100 gamma-rays from a flash, we
will be able to see thousands or tens of thousands of gammas from close up,
and therefore learn much more about each event.
Do you foresee any social or political implications for
We are looking carefully into the radiation dose that could be received by
someone in an airplane above a thunderstorm. It would be a very rare event
for someone in that position to be hit by a TGF, but it might result in a
radiation dose higher than the recommended maximum exposures.
David M. Smith, Ph.D.
Associate Professor of Physics
Department of physics
University of California at Santa Cruz
Santa Cruz, CA, USA Web