Middle atmosphere dynamics with gravity wave interactions in the numerical spectral model: Zonal-mean variations

It is generally accepted that small-scale gravity waves (GW) produce the observed reversals in the zonal circulation and temperature variations of the upper mesosphere (e.g., Lindzen, 1981). There is evidence that GW also play an important role in the quasi-biennial oscillation (QBO) of the lower stratosphere, which can be generated by planetary waves (Lindzen and Holton, 1968). In the present paper, we summarize the modeling studies with the mechanistic numerical spectral model (NSM), which incorporates the Doppler spread parameterization for GW (Hines, 1997a and Hines, 1997b). Our studies illuminate the importance of GW filtering and momentum deposition associated with critical level absorption and wave braking. Numerical results from the 2D and 3D versions of the NSM show how these wave interactions generate in the zonal-mean: (a) annual and semi-annual oscillations, (b) QBO with related semi-decadal oscillation and solar cycle effects, and (c) monthly intra-seasonal oscillations.