The DOE E3SM coupled model version 1: Ocean Mean State biases and Historical Transient Variability.

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 a new river model, a variant of the Community Atmosphere Model (CAM), and new ocean and sea ice components based on the Model for Prediction Across Scales (MPAS) framework. The MPAS framework utilizes an unstructured mesh, allowing for seamless variation in model resolution. To establish the validity of the E3SMv1 model (and the MPAS framework), we have conducted the DECK simulations at the standard resolution of 100km atmosphere and 60-30 km ocean.The MPAS-Ocean and MPAS-Sea Ice mean state and biases are consistent with other CMIP5 ocean and sea ice component models. Progress towards reducing systematic model biases in E3SMv1 (e.g. ENSO variability, ocean heat uptake) has been made, but significant challenges remain. The E3SMv1 simulated AMOC at RAPID is on the weak end of CMIP5 models ( 12 Sv). As in other CMIP models, E3SMv1 exhibits excessive sea ice in the Labrador Sea. Finally, using Nino3 and 4 variability from the historical transient runs, we present a rough estimate of E3SMv1 internal model variability. Even with a limited ensemble size, we find E3SMv1 internal model variability is consistent with the CESM large ensemble.