What initiates a lightning strike? In the image above, multiple cloud-to-ground and cloud-to-cloud lightning strikes are observed during a night-time thunderstorm. (Courtesy: NOAA)

Cosmic rays interacting with water droplets within thunderclouds could play an important role in initiating lightning strikes. That is the claim of researchers in Russia, who have studied the radio signals emitted during thousands of lightning strikes. The work could provide new insights into how and why lightning occurs in the first place.
Although most people have witnessed a flash of lightning during a thunderstorm at some point in their lives, scientists still do not completely understand what triggers the discharge in the first place. Lightning has been studied for hundreds of years, yet while many possibilities for observation are available – there are about 40 to 50 lightning strikes per second across the globe – predicting the onset of a strike is difficult…. Read more at http://physicsworld.com/cws/article/news/2013/may/07/new-insights-into-what-triggers-lightning