Terrestrial gamma-ray flashes (TGFs) are bursts of gamma rays in the earth's atmosphere. TGFs have been recorded to last 0.2 to 3.5 milliseconds, and have energies of up to 20 MeV. They are probably caused by electric fields produced above thunderstorms.

Discovery

Terrestrial gamma-ray flashes were discovered in 1994 by BATSE , or Burst and Transient Source Experiment, on the Compton Gamma-Ray Observatory.

The newer RHESSI satellite has observed TGFs with much higher energies than those recorded by BATSE. In addition, the new observations show that approximately fifty TGFs occur each day. However, the number may be much higher than that due to the possibility of flashes in the form of narrow beams that would be difficult to detect.

Mechanism

During a thunderstorm, negative charge creates an electric field in the mesosphere. The field attracts electrons, which collide with nitrogen molecules to free more electrons. The electrons travel at relativistic speeds, and they emit bremsstrahlung in the form of gamma rays after collisions with nuclei .

See Also

• Gamma-ray bursts

References

• Barrington-Leigh, C.P. (n.d.). Terrestrial Gamma-ray Flashes after CGRO: prospects for HESSI. Retrieved April 2, 2005, from University of California Berkeley, Space Physics Research Group.

• McKee, Maggie (Feb. 17, 2005). Earth creates powerful gamma-ray flashes. New Scientist.

• Stephens, Tim (Feb. 21, 2005). New satellite observations of terrestrial gamma-ray flashes reveal surprising features of mysterious blasts from Earth. UC Santa Cruz Currents.