QBO, gravity waves, and deep convection responses to surface warming in GFDL simulations

Changes in gravity waves, convection, and the Quasi-Biennial Oscillation (QBO) are investigated using the Geophysical Fluid Dynamics Laboratory’s (GFDL) Global AtmosphericModel, which now incorporates a gravity wave drag scheme (the Beres scheme) that is sensitive to details of convective latent heating. Simulationswith present-day conditions are compared to Tropical Rainfall Measuring Mission (TRMM) observations and to simulations with warmer surface conditions. Compared to TRMM, the present-day simulations include fewer of the strongest but more of the deepest convection events. A unique aspect of this GFDL model application of the Beres scheme is the use of a prognostic convective area parameter, whereas previous model applications used a fixed convective areawithin the scheme. The prognostic convective area leads to more gravity wave sourceswith higher heating rates and shorter heating depths, with notable impacts on the simulation of the QBO. In particular, when applying the prognostic convective area, westward gravity wave momentum flux increases at low-phase speeds, leading to an improved QBO simulation in the tropical lowermost stratosphere. With warmer surface temperatures, the simulated convection extremes become both deeper and stronger. The QBO period shortens when the surface is warmer, as reported in earlier studies. But use of the prognostic convective area provides new sensitivity to the convection details, resulting in smaller changes to gravity wave fluxes and QBO period under surface warming.