The transient critical‐level interaction in a Boussinesq fluid

Abstract

A numerical model was used to examine the consequences of transience and nonlinearity in the critical‐level interaction of an internal gravity wave. Wave packets in a shear flow were observed to evolve as predicted by the linear, initial‐value results of Booker and Bretherton (1967) until convectively unstable layers evolved. Once formed, such layers were found to break down via a convective instability, presumably resulting in the turbulent dissipation of the incident wave packet. Several simulations were used to illustrate the transient stabilization of, and the Eulerian mean flow accelerations induced by, critical‐level interactions. Other simulations were performed to examine the evolution of a wave packet in a time‐dependent shear flow. The latter suggest that critical‐level absorption and wave action dissipation can be either greatly accelerated or effectively eliminated depending upon the tendency of the mean velocity shear. The implications of these findings for internal gravity wave propagation in the atmosphere and the oceans are discussed.

A non-hydrostatic and compressible 2-D model simulation of Internal Gravity Waves generated by convection

“…Fritts (1982) conducted a time dependent nonlinear numerical simulation of breakdown of IGWs and showed that IGWs break down due to the convective instability associated with the large amplitude resulting in the turbulent dissipation of the incident IGWs. Fritts et al (1994) recently reported the detailed evolution of the breakdown of IGWs and the generation of mean flow using a time dependent nonlinear three-dimensional model, in which they focused their attention to the IGW breaking phenomena.…”

Small‐scale gravity waves near the mesopause observed by four all‐sky airglow imagers

“…It is well known that gravity waves can carry a significant amount of momentum flux to the mtsopause region from lower altitudes [e.g., Lindzen, 1981;Fritts, 1983]. The momentum is transferred when the gravity waves are broken or damped at these altitudes due to a rapid change in background wind and temperature profiles [c.g., Lindzen, 1981;Fritts, 1982Fritts, , 1984. [1997] studied the dispersion relation of small-scale waves obtained by an all-sky imager using background wind data from a MF radar.…”

The climatological model of the gravity wave ensemble at the middle atmosphere heights

“…First of all, a number of numerical simulations of the incidence of internal wave on a shear layer containing a critical level, shows that complex transfer processes occur between the mean ow and the wave ÿeld (Booker and Bretherton, 1967;Brown and Stewartson, 1980;Fritts, 1982;Winters and Riley, 1992). In such ows some of the wave energy may be absorbed, some may be re ected from the layer, some may be ducted along the guide and another fraction may be transmitted through the critical level.…”