Mechanisms in Regulating the Quasi-Biennial Oscillation in Exascale Earth System Model Version 2

The update to the deep convection parameterization in the energy exascale Earth system model version 2 (E3SMv2) makes the simulated quasi-biennial oscillation (QBO) have a shorter period than without the update when other tunable parameters the same since the update makes convection more intense but less frequent while leaving the time-mean convective heating tendency almost unchanged. Amplitudes of momentum fluxes of parameterized gravity waves (GWs) are intensified since they are determined by the square of convective heating tendency. In addition, stronger planetary waves are simulated in E3SMv2 with the convection scheme update, partially due to the tropospheric precipitation change. Furthermore, there is evidence that planetary waves are intensified in the stratosphere due to the dissipation of enhanced parameterized GWs. These factors are found to be responsible for modulating the QBO simulated in E3SMv2.