Gravity wave saturation in the middle atmosphere: A review of theory and observations

Abstract

This paper provides a review of recent advances in our understanding of gravity wave saturation in the middle atmosphere. A brief discussion of those studies leading to the identification of gravity wave effects and their role in middle atmosphere dynamics is presented first. This is followed by a simple development of the linear saturation theory to illustrate the principal effects. Recent extensions to the linear saturation theory, including quasi‐linear, nonlinear, and transient effects, are then described. Those studies addressing the role of gravity wave saturation in the mean circulation of the middle atmosphere are also discussed. Finally, observations of gravity wave motions, distribution, and variability and those measurements specifically addressing gravity wave saturation are reviewed.

Radar observations of gravity waves over Jicamarca, Peru, during the CADRE campaign

“…Much of the current understanding of momentum flux relies on theory and numerical models. Fritts [1984] used simple theoretical arguments to predict the proportion of momentum flux due to gravity wave motions in the high-and low-frequency parts of the spectrum. A …”

The nonlinear effects on the characteristics of gravity wave packets: dispersion and polarization relations

“…A number of theoretical studies of gravity waves have emphasized the importance of gravity waves in transporting energy and momentum from lower atmosphere to the upper middle atmosphere (Lindzen, 1981;Holton, 1982Holton, , 1983Fritts and Rastogi, 1985), which leads to the coupling of di erent layers in atmosphere and plays an important role in energy balance in the global middle and upper atmosphere. Since the 1960s it is clearly understood that when a gravity wave packet propagates in the atmosphere, the background¯ow will be accelerated because of the transient nature of a wave packet, moreover, since the atmospheric density decreases exponentially with increasing height, upgoing gravity waves excited in the troposphere reach such great amplitudes near the mesosphere that they break and cause intensive turbulence (Lindzen, 1981;Fritts, 1984). These e ects are considered to be signi®cant for the formation of the global thermal and wind structure (Fritts, 1984).…”

“…Since the 1960s it is clearly understood that when a gravity wave packet propagates in the atmosphere, the background¯ow will be accelerated because of the transient nature of a wave packet, moreover, since the atmospheric density decreases exponentially with increasing height, upgoing gravity waves excited in the troposphere reach such great amplitudes near the mesosphere that they break and cause intensive turbulence (Lindzen, 1981;Fritts, 1984). These e ects are considered to be signi®cant for the formation of the global thermal and wind structure (Fritts, 1984).…”

“…Because of the exponential increase of gravity wave-associated disturbance velocities with height, it is believed that the nonlinearity will strongly a ect the propagation of gravity waves in the middle and upper atmosphere. Therefore after the 1980s, many authors have thrown light on the nonlinear e ects of gravity waves and a number of valuable approaches (Lindzen, 1981;Fritts, 1984;Dewan and Good, 1986;Hines, 1991;Gardner, 1994) have been presented. However, all these approaches are carried out by making a crucial assumption: that all gravity waves, including those in the nonlinear circumstance, obey the polarization and dispersion relations of gravity waves.…”

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.…”