On shear-generated gravity waves that reach the mesosphere. Part II: Wave propagation

The propagation of Kelvin-Helmholtz (KH) shear-generated gravity waves through the summer stratosphere is investigated using ray tracing, taking into account back-reflection as well as wave dissipation due to precritical-layer breaking, radiative damping, and viscous diffusion. It is found that the transmission rate of upward-eastward waves to the mesosphere is surprisingly good, provided that the horizontal scale of the waves is large enough to prevent back-reflection. A rough upper bound on the net momentum flux into the mesosphere due to a large ensemble of mutually incoherent KH-generated clear-air turbulence events is then estimated, using reasonable-looking assumptions about the statistics of such events. It is found that on this basis the wave source cannot safely be neglected in the global angular momentum budget.