By Vladimir Brezina
As kayakers, we are intimately familiar with waves on the surface of the water. But waves produced by the same basic physical mechanism—gravity waves—can form anywhere where a perturbation sets off oscillations in a density-stratified fluid. The surface of the water—an interface between two fluids of different densities, water and air—is just the most familiar location. But essentially similar waves, albeit now internal rather than surface waves, can form deep below in the water, and high above in the air.