Gravity Waves:

We've all seen waves on the surface of a lake or a puddle. If we throw a rock into puddle it initially pushes the water down.  However, after the rock has sunk the waves continue because the water wants to return to a calm level and as the water is pushed downwards it displaces the water next to it upwards. This type of wave is called a gravity wave because gravity acts to restore the surface to the right level.

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Gravity waves can also happen inside the atmosphere when cooler more dense parcels of air are pushed upwards.
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This often happens when winds blow over mountain ranges -
we can see bands in the clouds where cool air is pushed upwards and clear sky where the air decends again. Diverging Air
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These internal atmospheric gravity waves are able to transform energy from the winds blowing over the mountains into energy associated with the wave motion.  These waves can then travel upwards and transport energy from the troposphere into the stratosphere and beyond.
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As the gravity waves travel upward they can get very large and can break (just like waves on a beach).  When the waves reach a certain height where their speed is equal to the mean wind speed of the vortex the wave can break and deposit it's energy into the mean flow.

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