Happy New Year! Don’t Get Zapped By Gamma Rays

Lightning, even from common storms, can create flashes of invisible gamma rays that shoot into Earth’s upper atmosphere. Credit: Sebastien D’ARCO

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.

Updrafts and downdrafts in thunderstorm clouds electrically charge snow and water which creates pockets of positive and negative charge within the cloud. When strong enough to break through air’s insulating ability, the charges join and a lightning flash occurs.  Walk on carpeting and touch a metal doorknob to experience on a tiny scale what happens in a thundercloud.  Credit: NASA

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.

In this photo illustration, a burst of electrons stimulated by a lightning bolt leaves the top of a thunderhead. For every 2,000 lightning strikes that occur within a storm cloud, Fermi detects one gamma ray flash. Credit: NASA

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.

When a speeding electron leaving a thunderstorm strikes an air molecule, a gamma ray is emitted. Credit: NASA

“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.”

A sample of radar data gathered by the world-wide lightning monitoring networks on several different storms. One of the most interesting findings when comparing radar and Fermi data is that even the weakest storms produce TGFs. Credit: NASA

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.

Lightning flashes over Lake Superior and downtown Duluth, Minn. US during a thunderstorm. Credit: Daniel Thralow

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.

2 Responses

  1. Bison fan forever.

    There is nothing more relaxing to be laying in bed at night an listening to the soft rumble of thunder in the distance; then drifting off to sleep.

    I love thunderstorm and lightening as it just amazes me how awesome and dramatic our weather really is.

    I remember flying into Mesa, AZ one summer evening. We were flying low over the foothills on our approach to the airport. Looking out the window I could see bolts of lightening and the clouds were an orangish color, in the low hanging haze covering the landscape. The plane was a rocking and ah rolling a bit, however, it was the most beautiful landings I have ever experienced.

    Thanks Bob for sharing all of your lessons of space, and our Earths amazing environment. I sincerely hope we can preserve it for future generations.

    Fargo, ND

    1. astrobob

      Bison fan,
      Thanks for sharing that evocative description of your flight. I think a lot of us feel the same way about the rumble of thunder making for good sleeping. You brought back a pleasant memory on a cold night here in Duluth.

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