If you didn't attend Thunder over Louisville yesterday, you may have still been able to hear the fireworks at your house, even if you live very far away from Downtown Louisville! Why did that happen this year when you may not have been able to hear it in the past?
It all comes down to a thing called an inversion. Down here in the lowest level of the atmosphere, the temperature drops as you go higher up in the atmosphere. However, under an inversion, that pattern flips. An inversion is a layer in the atmosphere when the temperature increases with height - a warmer layer. You also may have heard us describe this as a "cap" in the atmosphere. The layer of warmer air acts like a cap on top of the cooler layer. The image below from NC State University Extension helps illustrate what's happening.Â
When that inversion is really strong, it can curve sound waves back down toward the ground. Normally the sound waves would travel up into the air so you don't hear those noises as far away from the source. In a strong inversion, though, those sound waves can be refracted back toward the ground, reflect off the ground back into the air, and the cycle continues over longer horizontal distances. This explains why you may have actually heard the booms from the fireworks even if you don't live close to Downtown!
