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

Abstract

This work documents the first version of the U.S. Department of Energy (DOE) new EnergyExascale Earth System Model (E3SMv1). We focus on the standard resolution of the fully coupled physical model designed to address DOE mission-relevant water cycle questions. Its components include atmosphere and land (110-km grid spacing), ocean and sea ice (60 km in the midlatitudes and 30 km at the equator and poles), and river transport (55 km) models. This base configuration will also serve as a foundation for additional configurations exploring higher horizontal resolution as well as augmented capabilities in the form of biogeochemistry and cryosphere configurations. The performance of E3SMv1 is evaluated by means of a standard set of Coupled Model Intercomparison Project Phase 6 (CMIP6) Diagnosis, Evaluation, and Characterization of Klima simulations consisting of a long preindustrial control, historical simulations (ensembles of fully coupled and prescribed SSTs) as well as idealized CO 2 forcing simulations. The model performs well overall with biases typical of other CMIP-class models, although the simulated Atlantic Meridional Overturning Circulation is weaker than many CMIP-class models. While the E3SMv1 historical ensemble captures the bulk of the observed warming between preindustrial (1850) and present day, the trajectory of the warming diverges from observations in the Key Points: • This work documents E3SMv1, the first version of the U.S. DOE Energy Exascale Earth System Model • The performance of E3SMv1 is documented with a set of standard CMIP6 DECK and historical simulations comprising nearly 3,000 years • E3SMv1 has a high equilibrium climate sensitivity (5.3 K) and strong aerosol-related effective radiative forcing (-1.65 W/m 2 ) Correspondence to: Chris Golaz, golaz1@llnl.gov Citation: Golaz, J.-C., Caldwell, P. M., Van Roekel, L. P., Petersen, M. R., Tang, Q., Wolfe, J. D., et al. (2019). The DOE E3SM coupled model version 1: Overview and evaluation at standard resolution. second half of the twentieth century with a period of delayed warming followed by an excessive warming trend. Using a two-layer energy balance model, we attribute this divergence to the model's strong aerosol-related effective radiative forcing (ERF ari+aci = −1.65 W/m 2 ) and high equilibrium climate sensitivity (ECS = 5.3 K). Plain Language Summary The U.S. Department of Energy funded the development of a new state-of-the-art Earth system model for research and applications relevant to its mission. The Energy Exascale Earth System Model version 1 (E3SMv1) consists of five interacting components for the global atmosphere, land surface, ocean, sea ice, and rivers. Three of these components (ocean, sea ice, and river) are new and have not been coupled into an Earth system model previously. The atmosphere and land surface components were created by extending existing components part of the Community Earth System Model, Version 1. E3SMv1's capabilities are demonstrated by performing a set of standardized simulation experiments described by...

An Overview of the Atmospheric Component of the Energy Exascale Earth System Model

“…The lower forcing estimate, consistent with Figure 24 of Golaz et al (), is sensitive to the presence of aerosols from stratospheric volcanoes (absent during the period Golaz et al focused on), which explains most of the difference in the estimates, but emission sources of anthropogenic aerosols were also significantly higher during the earlier (1980–2004) period. The differences compared to the F2000 emissions used in C2 may also be partially explained by the SSTs differences used in C2 and column 3—clouds and cloud responses to aerosols and GHG can be sensitive to surface temperature and the 1980–2014 period is characterized by very large El Niño events not present in the SST climatologies used in C2 or the later time period analyzed in Golaz et al (). The differences in emissions and small differences in methodology compared to that used in Golaz et al () and the Forster et al () result showed that forcing estimates can depend significantly on the length of analysis interval indicated the sensitivity of the calculation.…”

“…Golaz et al () noted a lower amplitude estimate of −1.65 W/m 2 for the 1995–2015 time period. In this case, both simulations included the same volcanic aerosols in the stratosphere so the differences must be associated with the higher anthropogenic aerosol sources or higher SSTs compared to the period analyzed by Golaz et al (). Column 5 shows CAM5 values reported in Gettelman and Morrison () with a total aerosol ERF of −1.6 W/m 2 .…”

“…Table provides estimates of changes in TOA flux produced by differences in paired runs designed to expose differences between simulations as climate forcing agents are varied. Some of the runs used to estimate the model response to a forcing agent change in Table are drawn from Golaz et al (). Simulations from that study allow estimates of the model response to be made by comparing paired simulations with different forcing agents when surface temperature and volcanic stratospheric aerosols are varied by year (AMIP SSTs and a historical record of volcanoes were used).…”

Aerosols in the E3SM Version 1: New Developments and Their Impacts on Radiative Forcing

“…In all EAMv1 simulations, emissions of anthropogenic and biomass burning aerosols are from CMIP6 data sets, except that SOAG emissions are derived from SOA formation rates from a S2015 simulation to improve the SOA representation in the model, as described in section . Instead of using yearly varying aerosol emissions for 2006–2007, we use the average between 2000–2014 to represent PD aerosol conditions by removing the interannual variation in emissions (Yang et al, , ) and in aerosol forcing estimates (e.g., Golaz et al, ). PI emissions use the CMIP6 data set for year 1850.…”

The Summertime Precipitation Bias in E3SM Atmosphere Model Version 1 over the Central United States

“…Therefore, mitigating the precipitation bias over the Central United States is important to GCM development. This is particularly important for the U.S. Department of Energy‐funded Energy Exascale Earth System Model project (Bader et al, ) due to its strong focus on understanding regional climate changes, especially those related to the water cycle over North America (Golaz et al, ).…”