Impact of convectively generated gravity wave drag on the atmospheric general circulation

A parameterization scheme of gravity wave drag induced by cumulus convection (GWDC) is implemented in the Yonsei University atmospheric general circulation model (GCM) and the effects of GWDC on the zonal-mean flow and planetary waves are investigated through perpetual July simulations. The gravity wave stress at the cloud top is concentrated in the intertropical convergence zone (ITCZ) with its maximum value of 0.14 N/m2 near the tropopause due to deep cumulus clouds. The wave breaking occurs mainly in the upper troposphere and lower stratosphere. The maximum westerly acceleration in the ITCZ is 0.6 m/s/day, which is close to that observed. The zonal wind difference between the simulations with and without the GWDC parameterization is largest in the Southern Hemisphere (SH) midlatitude stratosphere, where a westerly jet exists, rather than in the major drag forcing region. The excessive westerly jet in the SH, which appears in the simulation without GWDC parameterization is alleviated significantly (7 m/s) by its inclusion. This result implies that the nonlinear process through planetary waves rather than direct drag forcing might play an important role in changing the zonal-mean flow. The analysis of the geopotential height perturbation revels that the amplification of the waves of zonal wavenumber 1 and 2 in the SH stratosphere is responsible for the change in the zonal-mean flow there. In particular, the wave amplitude of zonal wavenumber 2 significantly increases by the GWDC process in the SH midlatitude upper stratosphere.