I hope you have a happy and safe 2015, but when the weather warms and the first thunderstorm clouds billow darkly in the sky, consider one of the most remarkable things we’ve learned about them in recent years.
Storms are home to lighting and lighting produces gamma rays, nature’s hard-core radiation. They can bust up the DNA in your cells and make you very sick.
But don’t worry. Gamma rays aren’t out to get you. They leave the tops of thunderclouds 9-11 miles overhead and travel from there into space. Using new techniques to increase the sensitivity of NASA’s Fermi Gamma-ray Space Telescope we now know that terrestrial gamma ray flashes or TGFs or much more common than originally thought. Scientists estimate that some 1,100 TGFs occur each day, but the number may be much higher if low-altitude flashes are being missed.
Just how does the most energetic radiation in the known universe get produced in clouds? Inside a thunderhead, powerful winds slam water droplets and snow flakes to collide and develop an electrical charge causing different parts of the clouds to develop positive and negative charges. When the strength of oppositely charged regions becomes strong enough to resist the insulating properties of air, the two connect and release their energy as a stroke of lightning.
Under the right conditions, the upper part of the lightning bolt disrupts the storm’s electrical field and releases an surge of electrons (electricity) into the atmosphere above the cloud. When these fast-moving electrons are deflected by air molecules, they emit gamma rays and create a TGF.
Most of the bursts occur in 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,” said Michael Briggs, assistant director of the Center for Space Plasma and Aeronomic Research and a member of the satellite’s Gamma-ray Burst Monitor team. “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.”
Scientists using the Fermi Space Telescope coordinate with the Total Lightning Network and World Wide Lightning Location Network to pinpoint the location of lightning discharges — and the corresponding signals from TGFs — to within 6 miles (10 km) anywhere on the globe.
While thunderstorms have the power to awaken primeval fear in our hearts, they continue to feed our amazement as we look deeper and learn more.