Let There Be Light(ning)!
2017-07-29 20:03:58.000 – Sam Webber, Summit Intern
The power of nature, in my opinion, is one of the most awe inspiring things to witness on Earth. One phenomenon that I find particularly intriguing is the power and unpredictability of lightning. Some may underestimate how dangerous lightning can actually be, and this is something that I have noticed throughout my internship as people have been casually walking around on the summit while thunderstorms approach the mountain; this is a VERY bad idea! While lightning is a beautiful display of how the forces of nature work, it is extremely dangerous and could take your life away faster than the blink of an eye. With that being said, let’s talk about the science behind lightning.
Figure 1: Lightning striking over hill tops. Photo taken from BBC.com.
While a lightning strike occurs in just a fraction of a second, there is so much more going on than just the flash of light that we are able to depict with the naked eye. If we were able to take a slice out of thunderstorm we would be able to see an incredible amount of water, both liquid and frozen. A vertical stream of air, called an “updraft”, acts to suspend these hydrometeors in the cloud and will cause rain drops and hailstones of all different sizes to form and collide with one another. When the hydrometeors collide, they actually begin to transfer electrons which cause the smaller ones to become positively charged and the larger to become negatively charged. Thus, the charges within the cloud are arranged in a way such that the base of the cloud primarily holds a negative charge (from larger and heavier hydrometeors) and the top holds a positive charge (from lighter and smaller hydrometeors). Are you still with me? Good!
Figure 2: Schematic of thunderstorm air flow and charge distribution. Image taken from Scientific Explorer.
Positive and negative charges are attracted to each other similar to how the north and south poles of magnets are attracted to one another. So, while the negative charge continues to accumulate at the base of the cloud and a primarily positive charge organizes at the surface, there is a continuous strengthening of the electric field. The electric field will continue to intensify until a “breakdown potential” is reached and the forces of nature take over; this is when lightning occurs. Bear with me for just a little longer!
A spark is initiated at the base of the cloud and causes a “stepped leader” to descend from the cloud base. The role of the stepped leader is to create a channel that will allow for electrons to flow from the cloud to the ground. A positively charged “streamer” extends vertically from the surface to meet the stepped leader and completes the electrical circuit between the cloud and the ground. A “return stroke” occurs when the stepped leader and the streamer make contact, and this is what we call lightning! The rapid discharge of electrons through the channel creates an electric current of roughly 30,000 amperes, which causes the air within the channel to get hot, REALLY HOT! Air within the channel is heated to a temperature of around 53,500⁰F (5 times hotter than the surface of the sun) and is forced to expand at astronomical rates, and this is what we call thunder.
Figure 3: Breakdown of stepped leader and streamer (leader) interactions. Image taken from Texas A&M Atmospheric Science department.
So, next time you hear a thunderstorm starting to roll in, do yourself a favor and get inside! Just because the storm is not over you, it does not mean that you cannot get struck; lightning can strike up to 10 miles away from its parent storm!
Sam Webber, Summit Intern