Hurricanes, Black Holes and Gamma Rays

If you're not following Marshall Shepherd on social media, you're missing out on an opportunity to learn about a whole spectrum of science-related topics that may never have crossed your mind previously. Shepherd, the Georgia Athletic Association Distinguished Professor  and the director for the program in atmospheric sciences at UGA, not only has his finger on the pulse of breaking news in the climate and weather research fields, he also writes about it for Forbes.

Most recently, Shepherd wrote about how flights in Arizona were often stiffled by the heat and why; why scienticists say Tangier Island sea levels are a threat to the island. Now, his most recent article brings together some unique topics--hurricanes, black holes and gamma rays. As it turns out, a new study highlights the discovery that black holes and hurricanes both have gamma rays and offers possible improvements for hurricane intensity forecasts. 

Gamma rays are a part of the electromagnetic spectrum and typically have the smallest wavelength. They are the most energetic form of light and are produced by the some of the most extreme radiation generating activities in the universe (destruction of atoms, an exploding supernova, decaying radioactive material, and black holes). According to new research published in the Journal of Geophysical Research: Atmospheres, we can add hurricanes to the list. Using the Fermi Gamma-ray Space Telescope (Fermi), NASA researchers reported finding 37 terrestrial gamma flashes (TGFs), which are submillisecond bursts of radiation, coming from tropical storms over the period 2008 to 2015. The TGFs are hypothesized to be generated by intracloud lightning in the thunderstorms associated with the tropical storms. According to NASA's Earth Observatory, the energy in a TGF is can be as much as 100 mega-electron volts or roughly the same radiation emitted by 400 chest X-rays.

Using very low frequency (VLF) radio measurements, the scientists identified the location of TGF-generating storms within the tropical storms. Their research suggests that weaker tropical cyclones (depressions and storms) were more likely to produce TGFs. Though the location was not dependent on being in the center of the storm for the weaker storms, the researchers found that TGFs were always found in the outer rainbands of hurricanes and typhoons. This is not surprising to many of us that do tropical meteorology research as previous studies have shown that the highest lightning rates in tropical cyclones are often at a distance from the center.

The outstanding NASA Earth Observatory website summarized the study findings:

....the phenomenon (TGFs) remained unknown until first detected in 1992 by NASA’s Compton Gamma-ray Observatory. Today, scientists continue TGF observations with the Gamma-ray Burst Monitor (GBM) on NASA’s Fermi Gamma-ray Space Telescope. With sweeping coverage of the celestial sky, the instrument primarily detects bursts of gamma rays that come from energetic explosions in distant galaxies. But since its launch in 2008, Fermi has also detected more than 4,000 TGFs arising in Earth’s atmosphere. One third of those have been pinpointed to individual storms. Scientists think the electric field within lightning storms causes electrons to accelerate upward in the atmosphere at speeds approaching that of light, which results in a so-called “electron avalanche.” As the electrons zip past air molecules, they are deflected, which causes them to emit gamma rays.

Weather-related research topics and climate change research continue to be at the forefront at UGA and Shepherd is just one of many scienticsts on our campus and around the world who try to promote scientific literacy in climate change topics and elucidate new research. Read the whole article here on gamma rays here and follow him on Twitter at @DrShepherd2013. You can also find tweets from the UGA department of atmospheric sciences at @UGAAtmosSci.