"When a fluid parcel is displaced on an interface or internally to a region with a different density, gravity tries to restore the parcel toward equilibrium resulting in an oscillation about the equilibrium state or wave orbit. Gravity waves on an air-sea interface are called surface gravity waves or surface waves while internal gravity waves are called internal waves. Ocean waves generated by wind are examples of gravity waves, and tsunamis and ocean tides are others."
If gravity waves were doing that, you'd see trees, cars, homes and puppies get picked up and dropped repeatedly underneath those clouds. Plus, it might rain dirt and that would be awesome.
You bunch of fancy fuckin' ivory tower nerds. Nobody cares what kind of waves they are, except that they're awesome. I'ma call 'em science waves and go watch the game.
We live at the bottom of a sea... A sea of air! It's just much less dense than, let's say ground or water. That's why they pile up lower than air and form seas of their own.