09 April 2019

The DOE E3SM Coupled Model Version 1: Overview and Evaluation at Standard Resolution

A study documents and evaluates the performance of E3SMv1, the first version of the DOE Energy Exascale Earth System Model.

Science

E3SMv1 is the first version of the DOE Energy Exascale Earth System Model, a fully-coupled physical model designed to address DOE mission-relevant water cycle questions. In its standard-resolution configuration, E3SMv1 components include atmosphere and land (110km grid spacing), ocean and sea ice (60km in the mid-latitudes and 30km at the equator and poles), and river transport (55km) models. E3SMv1 was branched from the Community Earth System Model (CESM1) and has evolved significantly since; notable changes include:

  • E3SM Atmosphere Model (EAMv1) component with a spectral-element (SE) dynamical core, increased vertical resolution, and substantially revamped physics and the capability of regional grid refinement.
  • New ocean and sea-ice components based on the Model for Prediction Across Scales (MPAS) framework that uses Spherical Centroidal Voronoi Tessellations (SCVTs) for multi-resolution modeling.
  • New river transport model, Model for Scale Adaptive River Transport (MOSART), for a more physically based representation of riverine processes.
  • E3SMv1 land model (ELM) is based on the Community Land Model Version 4.5 (CLM4.5) with new options for representing soil hydrology and biogeochemistry.

The performance of E3SMv1 is evaluated by means of a standard set of Coupled Model Intercomparison Project Phase 6 Diagnosis, Evaluation, and Characterization of Klima (CMIP6 DECK) simulations. These simulations represent a total of nearly 3000 simulated years and are part of DOE’s contributions to CMIP6. 

Impact

In 2013, the US Department of Energy (DOE) developed a report summarizing observed long-term trends that, if continued for several decades, would have major impacts on the energy sector [U.S. Department of Energy, 2013]. Among these were regional trends in air and water temperatures, water availability, storms, and heavy precipitation, coastal flooding and sea-level rise. The ability to simulate and predict significant, long-term changes in these environmental variables important to energy-sector decisions required capabilities beyond the existing state-of-the-science Earth system models. The Energy Exascale Earth System Model (E3SM) project was conceived to meet this mission need. With the release of E3SMv1 and the initial set of simulations described in this study, DOE now has the capabilities to examine long-term changes in environmental variables impacting the energy sector. These capabilities will be further augmented in the near future with the addition of a higher-resolution version of E3SMv1, as well as future predictions simulations.

 

Summary

The performance of E3SMv1 is examined with a set of experiments from the CMIP6 DECK. The simulated climate over the course of the multi-century pre-industrial control simulation is stable with very little drift in global mean surface air temperature and seasonal range in sea ice area. The present-day climate compares favorably with an ensemble of 45 CMIP5 models. For most atmospheric variables, E3SMv1 falls within the top 25-percentile. But E3SMv1 is also subject to biases common to many models (e.g., stratocumulus coverage, double ITCZ, weak Atlantic Meridional Overturning Circulation, excessive sea ice concentrations in the Labrador Sea).

E3SMv1 has a much-improved representation of the Madden Julian Oscillation (MJO) in strength, propagation characteristics and the explained intra-seasonal variance compared to CESM1. The MJO is generally thought to play a role in ENSO initiation, monsoon active break cycles, tropical cyclogenesis, and remote teleconnection effects, therefore its accurate simulation is key. E3SMv1 also simulates well the frequency and spatial pattern associated with ENSO events which have a considerable impact on North American precipitation.

Historical simulations capture the bulk of the observed warming from 1850 to 2014, but the warming diverges from observations in the second half of the 20th century with a period of delayed warming followed by an excessive warming trend. We attribute this to the model’s strong aerosol-related effective radiative forcing (ERFari+aci = -1.65 W m−2) and high equilibrium climate sensitivity (ECS = 5.3 K).

Contact
Chris Golaz
Lawrence Livermore National Laboratory
Publications
Golaz, J, PM Caldwell, LP Van Roekel, MR Petersen, Q Tang, JD Wolfe, G Abeshu, et al.  2019.  "The DOE E3SM Coupled Model Version 1: Overview and Evaluation at Standard Resolution."  Journal of Advances in Modeling Earth Systems.  https://doi.org/10.1029/2018ms001603.