Link between orographic gravity wave parameterizations and resolved dynamics in CMIP6 models.

Internal gravity waves (GWs) have an important influence on the atmospheric energy transport and momentum budget. Consideration of the GWs – related processes is necessary in modelling and conceptual models of the atmosphere. GWs cover a broad spectrum of wavelengths from few to thousands of kilometres. Hence, they cannot be fully resolved by the global climate models (GCMs) and have to be parameterized. Although recent efforts with satellite observations and high-resolution models have been improving tuning and constraints of the GWs parameterizations, there is still a large uncertainty concerning the effects of GWs in GCMs. This is unwanted due to large impact of GWs on the atmospheric dynamics.

In our research we focus on orographic GW (OGW) parameterizations used in CMIP6 simulations. We compare the OGW induced drag from 7 different OGW parameterizations used in 9 different models, establishing the simulation-unique tuning of free parameters for majority of them. The comparison shows large, unexpected differences between simulations, which can be partly traced to the tuning or type of the parameterization. We also analyze intermodel differences in zonal mean winds and Eliassen-Palm flux divergence to trace the effects of the differences in OGW drag. Particularly, our results demonstrate a strong correlation between resolved wave drag and OGW drag in the models. Overall, our study gives an additional motivation for further improvements of the OGW parameterization schemes, with the aim of lowering the uncertainty of the future climate projections.