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This work documents version two of the Department of Energy's Energy Exascale Earth System Model (E3SM). E3SMv2 is a significant evolution from its predecessor E3SMv1, resulting in a model that is nearly twice as fast and with a simulated climate that is improved in many metrics. We describe the physical climate model in its lower horizontal resolution configuration consisting of 110 km atmosphere, 165 km land, 0.5° river routing model, and an ocean and sea ice with mesh spacing varying between 60 km in the mid-latitudes and 30 km at the equator and poles. The model performance is evaluated with Coupled Model Intercomparison Project Phase 6 Diagnosis, Evaluation, and Characterization of Klima simulations augmented with historical simulations as well as simulations to evaluate impacts of different forcing agents. The simulated climate has many realistic features of the climate system, with notable improvements in clouds and precipitation compared to E3SMv1. E3SMv1 suffered from an excessively high equilibrium climate sensitivity (ECS) of 5.3 K. In E3SMv2, ECS is reduced to 4.0 K which is now within the plausible range based on a recent World Climate Research Program assessment. However, a number of important biases remain including a weak Atlantic Meridional Overturning Circulation, deficiencies in the characteristics and spectral distribution of tropical atmospheric variability, and a significant underestimation of the observed warming in the second half of the historical period. An analysis of single-forcing simulations indicates that correcting the historical temperature bias would require a substantial reduction in the magnitude of the aerosol-related forcing.

This work documents the first version of the U.S. Department of Energy (DOE) new Energy Exascale 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 CO2 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 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 (ERFari+aci = −1.65 W/m2) and high equilibrium climate sensitivity (ECS = 5.3 K).

Some ocean modeling studies have identified a potential tipping point from a low to a high basal melt regime beneath the Filchner–Ronne Ice Shelf (FRIS), Antarctica, with significant implications for subsequent Antarctic ice sheet mass loss. To date, investigation of the climate drivers and impacts of this possible event have been limited because ice-shelf cavities and ice-shelf melting are only now starting to be included in global climate models. Using a global ocean–sea-ice configuration of the Energy Exascale Earth System Model (E3SM) that represents both ocean circulations and melting within ice-shelf cavities, we explore freshwater triggers (iceberg melt and ice-shelf basal melt) of a transition to a high-melt regime at FRIS in a low-resolution (30 km in the Southern Ocean) global ocean–sea-ice model. We find that a realistic spatial distribution of iceberg melt fluxes is necessary to prevent the FRIS melt regime change from unrealistically occurring under historical-reanalysis-based atmospheric forcing. Further, improvement of the default parameterization for mesoscale eddy mixing significantly reduces a large regional fresh bias and weak Antarctic Slope Front structure, both of which precondition the model to melt regime change. Using two different stable model configurations, we explore the sensitivity of FRIS melt regime change to regional ice-sheet freshwater fluxes. Through a series of sensitivity experiments prescribing incrementally increasing melt rates from the smaller, neighboring ice shelves in the eastern Weddell Sea, we demonstrate the potential for an ice-shelf melt "domino effect" should the upstream ice shelves experience increased melt rates. The experiments also reveal that modest ice-shelf melt biases in a model, especially at coarse ocean resolution where narrow continental shelf dynamics are not well resolved, can lead to an unrealistic melt regime change at downstream ice shelves. Thus, we find that remote connections between melt fluxes at different ice shelves are sensitive to baseline model conditions. Our results highlight both the potential and the peril of simulating prognostic Antarctic ice-shelf melt rates in a low-resolution global model. [ABSTRACT FROM AUTHOR]

Coupled ice sheet-ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions of the West Antarctic Ice Sheet (WAIS). Here we describe computational experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the Ice Shelf-Ocean MIP second phase (ISOMIP+) and coupled ice sheet-ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for the evaluation of the participating models.

The Marine Ice Sheet and Ocean Model Intercomparison Project – phase 2 (MISOMIP2) is a natural progression of previous and ongoing model intercomparison exercises that have focused on the simulation of ice-sheet and ocean processes in Antarctica. The previous exercises motivate the move towards realistic configurations as well as more diverse model parameters and resolutions. The main objective of MISOMIP2 is to investigate the performance of existing ocean and coupled ice-sheet–ocean models in a range of Antarctic environments, through comparisons to observational data. We will assess the status of ice-sheet–ocean modelling as a community and identify common characteristics of models that are best able to capture observed features. As models are highly tuned based on present-day data, we will also compare their sensitivity to prescribed abrupt atmospheric perturbations leading to either very warm or slightly warmer ocean conditions compared to present-day. The approach of MISOMIP2 is to welcome contributions of models as they are, including global and regional configurations, but we request standardised variables and common grids for the outputs. We target the analysis on two specific regions, the Amundsen Sea and the Weddell Sea, since they describe two different ocean environments and have been relatively well observed compared to other areas of Antarctica. An observational 'MIPkit' synthesizing existing ocean and ice sheet observations for a common period is provided to evaluate ocean and ice sheet models in these two regions. [ABSTRACT FROM AUTHOR]

The Marine Ice Sheet and Ocean Model Intercomparison Project - phase 2 (MISOMIP2) is a natural progression of previous and ongoing model intercomparison exercises that have focused on the simulation of ice-sheet and ocean processes in Antarctica. The previous exercises motivate the move towards realistic configurations as well as more diverse model parameters and resolutions. The main objective of MISOMIP2 is to investigate the performance of existing ocean and coupled ice-sheet-ocean models in a range of Antarctic environments, through comparisons to observational data. We will assess the status of ice-sheet-ocean modelling as a community and identify common characteristics of models that are best able to capture observed features. As models are highly tuned based on present-day data, we will also compare their sensitivity to prescribed abrupt atmospheric perturbations leading to either very warm or slightly warmer ocean conditions compared to present-day. The approach of MISOMIP2 is to welcome contributions of models as they are, including global and regional configurations, but we request standardised variables and common grids for the outputs. We target the analysis on two specific regions, the Amundsen Sea and the Weddell Sea, since they describe two different ocean environments and have been relatively well observed compared to other areas of Antarctica. An observational "MIPkit" synthesizing existing ocean and ice sheet observations for a common period is provided to evaluate ocean and ice sheet models in these two regions. [ABSTRACT FROM AUTHOR]

Some ocean modeling studies have identified a potential tipping point from a low to high basal melt regime beneath the Filchner-Ronne Ice Shelf (FRIS), Antarctica, with significant implications for subsequent Antarctic Ice Sheet mass loss. To date, investigation of the climate drivers and impacts of this possible event have been limited, because ice-shelf cavities and ice-shelf melting are only now starting to be included in global climate models. Using a version of the Energy Exascale Earth System Model (E3SM) that represents both ocean circulations and melting within ice-shelf cavities, we explore freshwater triggers of a transition to a high melt regime at FRIS in a low resolution (30 km in the Southern Ocean) global ocean-sea ice model. We find that a realistic spatial distribution of iceberg melt fluxes is necessary to prevent the FRIS melt regime change from unrealistically occurring under historical reanalysis-based atmospheric forcing. Further, improvement of the default parameterization for mesoscale eddy mixing significantly reduces a large regional fresh bias and weak Antarctic Slope Front structure, both of which precondition the model to melt regime change. Using two different stable model configurations, we explore the sensitivity of FRIS melt regime change to regional ice-sheet freshwater fluxes. Through a series of sensitivity experiments prescribing incrementally increasing melt rates from the smaller, neighboring ice shelves in the eastern Weddell Sea, we demonstrate the potential for an ice-shelf melt ''domino effect'' should the upstream ice shelves experience increased melt rates. The experiments also reveal that modest ice-shelf melt biases in a model, especially at coarse ocean resolution where narrow continental shelf dynamics are not well resolved, can lead to unrealistic melt regime change downstream, and these ice-shelf melt teleconnections are sensitive to baseline model conditions. Our results highlight both the potential and the peril of simulating prognostic Antarctic ice-shelf melt rates in a low-resolution, global model. [ABSTRACT FROM AUTHOR]

Antarctic Bottom Water is an important component of Earth's climate system. Its formation occurs through oceanatmosphere- sea ice flux interactions in coastal and open ocean polynyas around Antarctica. In this paper, we investigate Antarctic dense water formation in the high-resolution version of the Energy Exascale Earth System Model (E3SM-HR). The model is able to reproduce the major Antarctic coastal polynyas, though they are smaller in area compared to observations. E3SM-HR also simulates several occurrences of open-ocean polynyas (OOPs) in the Weddell Sea, at a higher rate than what the last 50 years of satellite sea ice observational record suggests, but similarly to other high-resolution Earth System Model simulations. Furthermore, the densest water masses in the model are formed within the OOPs, rather than on the continental shelf, as is typically observed. Biases related to the lack of dense water formation on the continental shelf are associated with overly strong atmospheric polar easterlies, which lead to a strong Antarctic Slope Front and hence too little communication between on and off continental shelf water masses. Strong polar easterlies also produce excessive southward Ekman transport, causing a build- up of sea ice over the continental shelf and enhanced ice melting in the summer season. This in turn produces water masses on the continental shelf that are overly fresh and less dense relative to observations. Our results indicate that the large-scale polar atmospheric circulation around Antarctica must be accurately simulated in models to properly reproduce Antarctic dense water formation. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.05.001 Byline: Xylar S. Asay-Davis (a), Philip S. Marcus (b), Michael H. Wong (a)(c), Imke de Pater (a) Keywords: Jupiter; atmosphere; Atmospheres; dynamics; Atmospheres; evolution Abstract: We show that between 1996 and 2006, the area circumscribed by the high-speed collar of the Great Red Spot (GRS) shrunk by 15%, while the peak velocities within its collar remained constant. This shrinkage indicates a dynamical change in the GRS because the region circumscribed by the collar is nearly coincident with the location of the potential vorticity anomaly of the GRS. It was previously observed that the area of the clouds associated with the GRS has been shrinking. However, the cloud cover of the GRS is not coincident with the location of its potential vorticity anomaly or any other of its known dynamical features. We show that the peak velocities of the Oval BA were nearly the same in 2000, when the Oval was white, and in 2006, when it was red, as were all of the other features of the two velocities fields. To measure temporal changes in the GRS and Oval, we extracted velocities from images taken with Galileo, Cassini, and the Hubble Space Telescope using a new iterative method called Advection Corrected Correlation Image Velocimetry (ACCIV). ACCIV finds correlations over image pairs with 10-h time separations when other automated velocity-extraction methods are limited to time separations of 2h or less. Typically, ACCIV velocities produced from images separated by 10h had errors that are 3-6 times smaller than similar velocities extracted from images separated by 2h or less. ACCIV produces velocity fields containing hundreds of thousands of independent correlation vectors (tie-points). Dense velocity fields are needed to locate the loci of peak velocities and other features. Author Affiliation: (a) Department of Astronomy, University of California, Berkeley, CA 94720, USA (b) Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA (c) Space Telescope Science Institute, Baltimore, MD 21210, USA Article History: Received 31 March 2008; Revised 14 April 2009; Accepted 21 April 2009

The E3SM Diagnostics Package (E3SM Diags) is a modern, Python-based Earth System Model (ESM) evaluation tool (with Python module name e3sm_diags), developed to support the Department of Energy (DOE) Energy Exascale Earth System Model (E3SM). E3SM Diags provides a wide suite of tools for evaluating native E3SM output, as well as ESM data on regular latitude longitude grids, including output from Coupled Model Intercomparison Project (CMIP) class models. E3SM Diags is modeled after the National Center for Atmospheric Research (NCAR) atmospheric model working group (AMWG) diagnostics package. In its version 1 release, E3SM Diags included a set of core essential diagnostics to evaluate the mean physical climate from model simulations. As of version 2.6, more process-oriented and phenomenon-based evaluation diagnostics have been implemented, such as analysis of the Quasi-biennial Oscillation (QBO), El Niño – Southern Oscillation (ENSO), streamflow, diurnal cycle of precipitation, tropical cyclones and ozone. An in-situ dataset from DOE’s Atmospheric Radiation Measurement (ARM) program has been integrated into the package for evaluating the representation of simulated cloud and precipitation processes. This tool is designed with enough flexibility to allow for the addition of new observational datasets and new diagnostic algorithms. Additional features include: customizable figures; streamlined installation, configuration and execution; and multiprocessing for fast computation. The package uses an up-to-date observational data repository maintained by its developers, where recent datasets are added to the repository as they become available. Finally, several applications for the E3SM Diags module were introduced to fit a diverse set of use cases from the scientific community. [ABSTRACT FROM AUTHOR]

The Energy Exascale Earth System Model (E3SM) is a new coupled Earth system model sponsored by the U.S Department of Energy. Here we present E3SM global simulations using active ocean and sea ice that are driven by the Coordinated Ocean-ice Reference Experiments II (CORE-II) interannual atmospheric forcing data set. The E3SM ocean and sea ice components areMPAS-Ocean and MPAS-Seaice, which use the Model for Prediction Across Scales (MPAS) framework and run on unstructured horizontal meshes. For this study, grid cells vary from 30 to 60 km for the low-resolution mesh and 6 to 18 km at high resolution. The vertical grid is a structured z-star coordinate and uses 60 and 80 layers for low and high resolution, respectively. The lower-resolution simulation was run for five CORE cycles (310 years) with little drift in sea surface temperature (SST) or heat content. The meridional heat transport (MHT) is within observational range, while the meridional overturning circulation at 26.5°N is low compared to observations. The largest temperature biases occur in the Labrador Sea and western boundary currents (WBCs), and the mixed layer is deeper than observations at northern high latitudes in the winter months. In the Antarctic, maximum mixed layer depths (MLD) compare well with observations, but the spatial MLD pattern is shifted relative to observations. Sea ice extent, volume, and concentration agree well with observations. At high resolution, the sea surface height compares well with satellite observations in mean and variability. [ABSTRACT FROM AUTHOR]