April 29, 2002
April 28 - May 4 marks a week of National Lightning Safety Awareness. Lightning is one of nature's deadliest phenomena, and the Northern Hemisphere is approaching peak season as the weather warms. Over 70 people are killed annually by lightning in the US alone, with 2000 deaths each year worldwide. Lightning strikes somewhere on our planet over 100 times every second. Liquid water and ice within a convective storm cell acquire electrical charges as hydrometeors grow and interact. The smaller positively charged particles make it higher up into the cloud, while larger negatively charged particles remain lower. Electrical potentials of millions of volts betwen cloud and ground eventually overcome atmospheric resistance and discharge currents measured in the tens of thousands of amperes as a lightning bolt. The electrical conduit through the air can be heated to 20 or 30 thousand degrees C creating a shockwave of expanding air heard as thunder.
Dominic Cantin captured this image from the comfort (and relative safety) of his sitting room in Quebec City during a storm earlier this month.