As we head into the last bit of summer, we are all experiencing extremely hot and humid weather which is leading to those large and scary summer storms. We know it’s a summer evening when we see those lightning strikes and hear the rumbles of thunder amongst the graying sky. As much as we all are familiar with the sights and sounds of summer storms, do we know how they happen? Well it’s due to science, of course!
How does a storm develop?
On the hot days of summer, the sun will warm the ground, which in turn, warms the air. Humid air will start to rise as it gets hotter, because hot air is lighter than cold air. Humid air has a lot of moisture, so as the hot and humid air rises, the moisture from the air condenses. This means the air changes from a vapor phase to a liquid phase, forming water droplets. These water droplets come together in the atmosphere and form clouds. Raindrops start to fall from clouds, when the surrounding air can no longer hold the weight of the water droplets. Storms happen when the air within the cloud travel in different directions, causing a build up of different electrical charges. These electrical charges then release energy in the form of lightning and thunder
What is lightning and thunder?
The moving air in the clouds are quite strong. Downdrafts and updrafts of air move the water droplets all around the cloud. The water droplets are in a liquid phase at the bottom of the cloud and are in a solid phase (are frozen or are ice) at the top of the cloud. As the air moves the droplets from bottom to top and top to bottom the electrons of the water droplets are lost where the liquid and solid phases meet. This creates an electrical field, where the bottom of the cloud has a negative charge and the top has a positive charge. The atmosphere between the top and bottom insulates or separates the two fields. Lightning happens when the equilibrium (state of balance between two opposing forces) of the electric field is off. One of the charges becomes so powerful that it overpowers the insulation provided by the atmosphere and attracts the other charge.
Fun Fact: We can’t see most lightning strikes. Most lightning strikes during a storm occur inside the clouds!
When the electrical field within the cloud is off balance, it needs to find a pathway to release the built up charge or energy. The field will release the energy in a pathway that is easy and close. Most of the time the pathway is located within the cloud, but sometimes the pathway is to the ground. This is when we see lightning strikes, when the off balance electric field releases it charge towards the ground. As a storm cloud moves over the ground, the storm cloud’s overpowering negative charge is attracted to the ground’s positive charge. The release in charge, in the form of a lightning bolt strikes the ground, and when the bolt is about 100 yards away from the ground, objects like buildings or trees send up positive sparks to meet the bolt. The moment the opposing charges meet we can see the the enormous electric current that is created. In other words, we see lightning!
Fun Fact: When lightning strikes, it radiates heat, at temperatures as hot as 50,000 degrees Fahrenheit! The sun reaches temperatures of about 10,000 degrees Fahrenheit, so lightning is about 5 times hotter than the sun, which is crazy!
As lightning strikes, it heats the air around it. The extreme heat quickly increases the air pressure, allowing the heat to expand away from the strike fast. The expanding heat compresses the air surrounding the strike. The sudden compression of air causes a shock wave, which is why we hear a very loud boom or rumble of thunder when lightning strikes.
References:
1. https://scijinks.gov/lightning/
2. https://www.nssl.noaa.gov/education/svrwx101/lightning/
3. https://scied.ucar.edu/learning-zone/storms/how-thunderstorms-form
4. https://www.weather.gov/safety/lightning-temperature
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