The Implementation of Framework for Improvement by Vertical Enhancement Into Energy Exascale Earth System Model

The low cloud bias in global climate models (GCMs) remains an unsolved problem. Coarse vertical resolution in GCMs has been suggested to be a significant cause of low cloud bias because planetary boundary layer parameterizations cannot resolve sharp temperature and moisture gradients often found at the top of subtropical stratocumulus layers. This work aims to ameliorate the low cloud problem by implementing a new computational method, the Framework for Improvement by Vertical Enhancement (FIVE), into the Energy Exascale Earth System Model (E3SM). Three physics schemes representing microphysics, radiation, and turbulence as well as vertical advection are interfaced to vertically enhanced physics (VEP), which allows for these processes to be computed on a higher vertical resolution grid compared to the rest of the E3SM model. We demonstrate the better representation of subtropical boundary layer clouds with FIVE while limiting additional computational cost from the increased number of levels. When the vertical resolution approaches the large eddy simulation‐like vertical resolution in VEP, the climatological low cloud amount shows a significant increase of more than 30% in the southeastern Pacific Ocean. Using FIVE to improve the representation of low‐level clouds does not come with any negative side effects associated with the simulation of mid‐ and high‐level cloud and precipitation, that can occur when running the full model at higher vertical resolution. Plain Language Summary Most global climate models (GCMs) underestimate low‐level clouds. Increasing vertical resolution in GCMs is intended to address some of the issues contributing to the problem. In this study, we have implemented a new computational method, known as the Framework for Improvement by Vertical Enhancement (FIVE). FIVE can increase the vertical resolution for select aspects of a GCM, and in this study, we apply FIVE to the Energy Exascale Earth System Model. Our results show that when the vertical resolution approaches 5–10 m, the low cloud amount shows a significant increase of more than 30% in the southeastern Pacific Ocean, while the FIVE method also prevents the simulations from being too computationally expensive. Key Points A novel computational framework, Framework for Improvement by Vertical Enhancement (FIVE), has been implemented into Energy Exascale Earth System Model (E3SM) and allows select physics to be computed on a higher vertical grid When the vertical resolution approa