Shuman Resonance. This is the frequency at which the Earth's magnetic
field resonates when excited by a powerful enough force. The first one I
learned about was lightning. I then looked further into this phenomenon
and found that tornadoes also cause this resonance to be excited, but
surprisingly enough in the air. Just before a tornado forms an 8Hz tone
is heard. This was discovered by a group of geophysicists who were using
listening devices for detecting, of all things, earthquakes, which also
happen to cause a resonance effect of 8Hz, both electromagnetically and
acoustically. Volcanoes also tend to excite this resonance before
erupting.
Physics of Open Ended Tubes
http://www.geocities.com/Vienna/3941/oetubes.html
Physics of Closed End Tubes
http://www.geocities.com/Vienna/3941/closedend.html