Recently, I learned about something really cool called Whistlers. It is a low frequency electromagnetic wave (audio range) produce by lighting striking the ionosphere. After the lightning strikes, an electromagnetic pulse is created and it travels very long distances. Due to dispersion, the higher frequencies of the pulse travel faster and with the proper equipment you can receive them and actually hear the sound of a whistle. It turns out these signals can come from "half around the world". Wow.
Here is a website where you can hear some of them: http://www.spaceweather.com/glossary/inspire.html
7 hours ago