Abstract
E3SMv1 is the first version of DOE’s Energy Exascale Earth System Model. E3SMv1 started from CESM1 but has since undergone significant changes. E3SMv1 includes new ocean and sea ice components based on the Model for Prediction Across Scales (MPAS) as well as a new river model, Model for Scale Adaptive River Transport (MOSART). In the atmosphere, the spectral-element (SE) dynamical core replaces the finite volume option and most of the physics has been enhanced or replaced. The number of vertical levels in the atmosphere was also more than doubled from 30 to 72 levels. CMIP6 simulations were run at the standard horizontal resolution of 100km atmosphere and 60-30 km ocean.
We present an overview of the modeled climate at standard resolution. Progress towards reducing systematic climate mode biases (such as improved clouds and precipitation) has been made, but significant challenges remain. E3SMv1 is a high sensitivity model with a strong aerosol-cloud forcing. E3SMv1 exhibits realistic ENSO variability, with long-term modulation in the control simulation. The E3SMv1 simulated AMOC is on the weak end of CMIP5 models (~12 Sv). Consistent with other CMIP5 models, E3SMv1 exhibits excessive sea ice in the Labrador Sea.
Finally, we compare regionally averaged SST from the historical transient ensemble to that from the CESM large ensemble. We find that even with a limited ensemble size, the E3SM ensemble captures much of the CESM large ensemble (40 members) spread. While E3SMv1 compares well with CESM large ensemble and reproduces the amount of warming observed over the 20th Century, the temporal evolution of that warming is unrealistic. We present evidence to suggest that both sensitivity and aerosol forcing are at fault.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. It is supported by the Energy Exascale Earth System Model (E3SM) project, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. IM Release LLNL-ABS-758563. The work has been approved for unlimited release LA-UR-18-28986.