Zonally non-uniform distribution of equatorial gravity waves in an atmospheric general circulation model

The results from an atmospheric general circulation model without gravity wave (GW) drag parameterization include quasi-biennial oscillation (QBO)-like oscillations in the equatorial lower stratosphere. The zonal distribution of gravity waves with periods of less than 3 days over the equatorial region is analyzed for 2 months ( July - August) during the westerly shear phase of the QBO. The westerly acceleration of the QBO is associated with the zonal forcing due to resolved waves of all components, and GWs account for about 60% of the forcing. The vertical flux of the zonal momentum of GWs in the upper troposphere has a non-uniform distribution. Large ( relatively small) magnitude upward fluxes with westerly ( easterly) momentum dominate in the Eastern ( Western) Hemisphere. The wave momentum flux divergence also varies with longitude. The westerly acceleration of the zonal wind due to GWs in the Eastern Hemisphere is much greater than that in the Western Hemisphere.