People Hear Strange Apocalyptic Sounds Coming From the Sky All Around the World

[frogmarch]

2. acoustic gravity waves?

Acoustic Gravity Waves

On a small scale, acoustic waves are driven by the elasticity of the air itself, and they are not dependent on gravity at all. For example, sound travels just fine through the air inside a manned spacecraft where the air is held in place by the pressure in the hull. On a large scale, however, the planet's atmosphere is held in place by gravity exactly as the ocean is, and much like the ocean, the atmosphere has waves sloshing around on it. Unlike the ocean, of course, there is no distinct surface to the atmosphere, which just becomes thinner and thinner with altitude. However, the basic principle is the same: gravity pulls high, dense regions of atmosphere back down where they belong, forcing neighboring regions up and thus sending out ripples of air.

The Importance of Acoustic Gravity Waves

Cirrus cloud formation is influenced by waves in the atmosphere. While these waves are acoustic, they occur at frequencies many times lower than humans can detect as sound, and are more easily measured by a barometer than by a microphone. Yet they do produce visible effects, as in the patterns of clouds. Understanding how they behave is useful for explaining and predicting weather and climate phenomena. Scientists have also studied ways of using acoustic gravity waves as a means to detect and monitor nuclear detonations.

Read more : http://www.ehow.com/info_8559357_acousticgravity-waves.html

They can be caused by earthquakes, volcanic eruptions, hurricanes, storms and tsunamis, among other things - oh, and "other things" would include huge energy flows from ginormous solar flares.