Gravity and gravity-inertial wave breakdown as a factor in turbulent layers

The breakdown of gravity and gravity-inertia (GI) waves, and the consequent generation of turbulence patches, can be caused by encounters of the waves with singular levels in the atmosphere. The simplest example of a singular level is one at which the wind reverses direction, e.g., from west to east- - usually referred to as a critical level. Theory, simulation, and observations agree on the generation of turbulence, possibly severe, in a layer of two or more kilometers thickness under a critical level when a gravity wave is propagated upward beneath it The longer GI wave has its own singular level, and theory and simulation predict breakdown when this level is attained by the wave. The turbulence may extend through a layer of two or more kilometers thickness, as with the gravity wave, or in certain circumstances, it may be confined to an extremely thin but very intense layer.