Journal of the Atmospheric Sciences · 2002 · 204 citations · 46 references
The study proposes that body forces generated during wave breaking act as a linear mechanism for producing secondary waves that propagate into the mesosphere and lower thermosphere. Deep 3D body forces efficiently generate high‑frequency, large‑vertical‑wavelength secondary waves with substantial momentum fluxes, but their spatial and temporal variability—especially when averaged over large horizontal scales—reduces wave frequency, increases horizontal wavelength, and diminishes flux, with efficiency largely latitude‑independent. The mechanism explains observed mean wind and secondary wave characteristics in 2D nonlinear models, shows that high spatial and temporal variability yields large momentum fluxes while slow variations produce negligible flux, and suggests that localized wave‑breaking body forces can generate high‑phase‑speed waves that significantly influence the momentum budget up into the thermosphere.
The authors propose that the body force that accompanies wave breaking is potentially an important linear mechanism for generating secondary waves that propagate into the mesosphere and lower thermosphere. While the focus of this paper is on 3D forcings, it is shown that this generating mechanism can explain some of the mean wind and secondary wave features generated from wave breaking in a 2D nonlinear model study. Deep 3D body forces, which generate secondary waves very efficiently, create high-frequency waves with large vertical wavelengths that possess large momentum fluxes. The efficiency of this forcing is independent of latitude. However, the spatial and temporal variability/intermittency of a body force is important in determining the properties and associated momentum fluxes of the secondary waves. High spatial and temporal variability accompanying a wave breaking process leads to large secondary wave momentum fluxes. If a body force varies slowly with time, negligible secondary wave fluxes result. Spatial variability is important because distributing “averaged” body forces over larger regions horizontally (as is often necessary in GCM models) results in waves with smaller frequencies, larger horizontal wavelengths, and smaller associated momentum fluxes than would otherwise result. Because some of the secondary waves emitted from localized body force regions have large vertical wavelengths and large intrinsic phase speeds, the authors anticipate that secondary wave radiation from wave breaking in the mesosphere may play a significant role in the momentum budget well into the thermosphere.
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