Australian Weather Calendar: December 2015

December photograph by David Stephens

Lightning over Adelaide Airport, South Australia

A night shift at Adelaide Airport Met Office in March 2013 let Rowland Beardsell combine his job as a Bureau of Meteorology weather observer with his passion for storm photography. Knowing a thunderstorm was expected that night, he set up his camera—a Canon 400D with a 177–40 mm lens—on the Met Office balcony with a timer set to begin a new exposure every 20 seconds. While Rowland was inside, typing an observation report, he saw a bright flash. 'Once I'd finished, about 20 seconds later, I raced out,' he says, 'and sure enough there it was on the camera'—he had captured not one lightning bolt, but three simultaneous strikes.

The rise and fall of droplets and ice crystals in a cloud cause areas of positive and negative electrical charge to build up. When the potential difference is great enough, an electrical discharge—lightning—occurs. Lightning heats the surrounding air, causing it to expand rapidly and produce the familiar sound of thunder. Most lightning occurs between or within clouds, but some strikes pass between clouds and the ground.

Diagram