Toward a More Physical Representation of Convective Gravity Waves in GFDL's GCM

We implemented in GFDL's global atmospheric model a parameterization for convective gravity waves, which explicitly describes the wave source based on the latent heating rates from the parameterized deep convection. The characteristics of the simulated Quasi-Biennial Oscillation (QBO) in the equatorial stratosphere depend on the tunable parameters in the convective gravity wave scheme. In particular, a larger efficiency factor or a smaller convective area leads to a shorter QBO period. A less-than-one scaling factor for the convective heating depth, though unphysical, is necessary for the model to simulate a realistic QBO over the lower stratosphere. Furthermore, we relax the assumption of constant convective area and replace it with the prognostic convective area diagnosed from the convection scheme. While the model with a constant convective area simulates a similar QBO to that with variable convective area at the present-day condition, it simulates a stronger reduction of the QBO period and the QBO amplitude in response to surface warming. Our results highlight the sensitivity of the simulated QBO in general circulation models to details of the parameterization for convective gravity waves.