Upside-down lightning strikes

11. Upward lightning strikes initiate on the ground and head skyward. These discharges, which usually begin at the top of tall and slender structures, pose a real risk for wind turbines. An EPFL study analyzes the mechanisms underlying this poorly understood phenomenon. Is lightning born of an angry sky? Not always. In some circumstances, it can also be initiated from the ground. Upward-moving discharges can easily be distinguished from downward ones by the inverted branches of the lightning which point to the clouds rather than the ground.