Lightning results from the electrical fields that are created when ice particles in clouds rub together. As electrical fields pass through the ice crystals, they become polarized and align, generating energy that is discharged when lightning flashes—at times creating so much energy that a bolt can heat the air it passes through to 50,000°F. Now, scientists have developed a new technique to detect those strong electrical fields and remotely track how lightning propagates in storm clouds.
In a new study, Biggerstaff et al. used dual-polarization radar, a type of tool that simultaneously transmits and receives both horizontal and vertical components of the electric fields within radar pulses. This type of instrument can tell the difference between rain, hail, sleet, and snow and even reveal the orientation of ice crystals in a distant thundercloud.
On 17 July 2012, the team waited for a small evening thunderstorm to arrive near Jacksonville, Fla., and then scanned the storm every 120 seconds. They also mapped lightning flashes within it, using a three-dimensional lightning location system called the 3-D VHF Lightning Mapping Array.
By combining the two data sets, the team identified where within the storm the electric fields were strongest and where intracloud lightning tended to propagate. The flashes began near the strongest electrical fields, where the ice crystals were all tilted the same way. The lightning channels then tended to propagate along the upper and lower boundaries of those strong electrical fields, the team concluded. The finding could help scientists predict the path of intracloud lightning, which includes the flashes that light up clouds from within, and the long, horizontal flashes, known as spider lightning, that bridge clouds across the sky. (Geophysical Research Letters, https://doi.org/10.1002/2017GL074610, 2017)
—Emily Underwood, Freelance Writer