Mean and variable forcing of the middle atmosphere by gravity waves

Recently we have begun to appreciate more fully the degree and the consequences of variability in gravity wave (GW) forcing of the middle atmosphere. Such variability arises for a number of reasons. GW sources in the lower atmosphere reflect the significant spatial and temporal variability of normal meteorological processes. GW amplitudes and characteristics are modulated by the wind and temperature fields through which they propagate. Nonlinear interactions and instability processes impose or amplify variability in energy and momentum transport and deposition. Finally, variability appears to be greatest among GWs occurring at the smaller spatial scales and periods that account for the majority of energy and momentum transports into the middle atmosphere. This paper both surveys recent findings and introduces new results.