Convectively Generated Gravity Waves in High Resolution Models of Tropical Dynamics

Abstract

AbstractWe investigate numerical models that display the transition of global climate modeling from coarse grids, at which convection and gravity waves are still parameterized, toward finer resolutions, where both are treated explicitly. Gravity waves generated by deep, tropical convection are examined by means of spectral analysis. We make use of the models' different setups to discuss the impacts of spatial resolution, the treatment of moist convection and the degree of model complexity, on convectively generated gravity waves. We find that substantially more gravity wave momentum flux is resolved by models with fine horizontal grid spacing, as the spectral slope is almost flat in zonal wave number space (∼k−1), until scales at which numerical diffusion sets in. However, we also find that, when well‐organized tropical storm systems of large scale are simulated with convection‐permitting resolution, the gravity wave variance may be enhanced at small scales and the spectral slope may flatten. We propose an explanation for this in the dynamical overshooting of convective updrafts that is expected to mechanically generate gravity waves. Further, we find that a parameterization of convection drastically reduces gravity wave momentum flux associated with tropical convection, as deep modes of latent heating and gravity waves are underestimated. Thus, its application is expected to have consequences for wave mean‐flow interaction in the middle atmosphere. The universal properties of the gravity wave spectrum that were found in observations and confirmed in analytical gravity wave models are successfully reproduced in our numerical simulations of tropical dynamics.