Not even sure if that qualifies as a pun, but stay with me here! In a press-release from Penn State, we hear that researchers there have now created a model that sheds light on in what conditions different kinds of lightning form. While the model does not really offer any predictive powers, I still find it quite cool, and I’ll grab the chance to write about something as awe-inspiring as lightning.

Lightning happens when electric charge escapes from the clouds and down to Earth. But there have to be rather specific conditions for this to happen, because air can not normally conduct electric charge. So what happens is that a cloud starts forming an electric charge somehow (and just how it does this is still up for debate), reaching very high voltage differences between the clouds and the ground. Once this difference is large enough, a process called dielectric breakdown happens, which basically means that the air becomes partially ionized, which in turn means that it can now conduct electricity, and transfer large amounts of electric-current down to the ground, striking golfers at will. The resulting sound you hear is because the extreme energy from the lightning heats up the air around it, which causes it to expand quickly, causing the boom. The video below shows a typical cloud-to-ground lightning as you’ve probably seen before.

This is at least the “normal” lightning as most of us think about it. There are however many different kinds of lightning, and in fact, most lightning never hits the ground, but travels within the clouds themselves. There is also another kind of lightning that goes from the cloud and to the ground, but is very different from a normal lightning. It is what is known as “Bolt from the blue” lightning, because it can indeed strike in what may seem like a clear, blue sky! This kind of lightning can travel 10’s of kilometers away from the actual storm cloud before making touchdown, and to top it all off, it is a lot more powerful than your run-of-the-mill lightning. The video here shows the lightning travelling inside a cloud (sorry, couldn’t find any video of a “Bolt from the blue”, but the picture on top shows one).

The research done by the Penn State team explains how and when these “Bolts from the blue” are created (using a mixture of observation and computer modeling) , as well as the other types of lightning. To quote the press release:

Our explanation provides a unifying view of how lightning escapes from a thundercloud
…
For intracloud lightning, the most common form of lightning, the transfer of charge occurs between the most negatively and most positively charged areas, the middle and upper parts of the cloud, respectively. Lightning that strikes the ground does so because precipitation or the storm’s progression creates an excess of net negative charge in the mid-levels of the cloud. This results in either a direct ground strike or a bolt from the blue.

I’m always in awe of lightning when I see it, it is truly amazing watching them and thinking of the power that nature possesses to light the entire sky up like that. For some perspective on their power, a normal cloud-to-ground lightning strike has 500Mega-Joules of energy and carries an electric current of around 1000 kilo-Amps. And now to put THAT into perspective, 0.01Amps is the lowest current a human can feel, 0.1-0.3 is enough to kill, and 6Amps is what you use in a defibrilator, compare that to the 1.000.000 Amps in lightning (figures taken from wikipedia article on electric shock).