Convection‐Permitting Simulations With the E3SM Global Atmosphere Model

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Quantification of dust aerosols in Earth System Models (ESMs) has important implications for water cycle and biogeochemistry studies. This study examines the global life cycle and direct radiative effects (DREs) of dust in the U.S. Department of Energy's Energy Exascale Earth System Model version 1 (E3SMv1), and the impact of increasing model resolution both horizontally and vertically. The default 1° E3SMv1 captures the spatial and temporal variability in the observed dust aerosol optical depth (DAOD) reasonably well, but overpredicts dust absorption in the shortwave (SW). Simulations underestimate the dust vertical and long‐range transport, compared with the satellite dust extinction profiles. After updating dust refractive indices and correcting for a bias in partitioning size‐segregated emissions, both SW cooling and longwave (LW) warming of dust simulated by E3SMv1 are increased and agree better with other recent studies. The estimated net dust DRE of −0.42 Wm−2 represents a stronger cooling effect than the observationally based estimate −0.2 Wm−2 (−0.48 to +0.2), due to a smaller LW warming. Constrained by a global mean DAOD, model sensitivity studies of increasing horizontal and vertical resolution show strong influences on the simulated global dust burden and lifetime primarily through the change of dust dry deposition rate; there are also remarkable differences in simulated spatial distributions of DAOD, DRE, and deposition fluxes. Thus, constraining the global DAOD is insufficient for accurate representation of dust climate effects, especially in transitioning to higher‐ or variable‐resolution ESMs. Better observational constraints of dust vertical profiles, dry deposition, size, and LW properties are needed.

Section: Discussionmentioning

confidence: 99%

Global Dust Cycle and Direct Radiative Effect in E3SM Version 1: Impact of Increasing Model Resolution

Feng

Wang

Rasch

et al. 2022

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“…Third, generalization of the conclusion from this modelbased analysis over four 0.5° × 0.5° grid cells to other regions with heterogeneous terrain needs to be further evaluated. Ongoing and future pioneering E3SM projects, for example, the 1 km gridded ELM implementation over the North American region under a hybrid CPU-GPU architecture of the Summit supercomputer and the global 3.25 km simulations in the DYnamics of the Atmospheric general circulation Modeled On Nonhydrostatic Domains Phase 2 model intercomparison (Caldwell et al, 2021), offer good opportunity to extend our findings.…”

Section: Discussionmentioning

confidence: 61%

Impacts of Sub‐Grid Topographic Representations on Surface Energy Balance and Boundary Conditions in the E3SM Land Model: A Case Study in Sierra Nevada

Hao

Bisht

Huang

et al. 2022

Sub‐grid topographic heterogeneity has large impacts on surface energy balance and land‐atmosphere interactions. However, the impacts of representing sub‐grid topographic effects in land surface models (LSMs) on surface energy balance and boundary conditions remain unclear. This study analyzed and evaluated the impacts of sub‐grid topographic representations on surface energy balance, turbulent heat flux, and scalar (co‐)variances in the Energy Exascale Earth System Model (E3SM) land model (ELM). Three sub‐grid topographic representations in ELM were compared: (a) the default sub‐grid structure (D), (b) the recently developed sub‐grid topographic structure (T), and (c) high spatial resolution (1KM). Additionally, two different solar radiation schemes in ELM were compared: (a) the default plane‐parallel radiative transfer scheme (PP) and (b) the parameterization scheme (TOP) that accounts for sub‐grid topographic effects on solar radiation. A series of offline simulations with the three grid discretization structures (D, T, and 1KM) and two schemes of solar radiation (TOP and PP) were carried out using the Sierra Nevada, California. 1KM simulations with TOP well capture the spatial heterogeneity of surface fluxes compared to Moderate Resolution Imaging Spectroradiometer remote sensing data. There are significant differences between TOP and PP in the 1‐km simulated surface energy balance, but the differences in mean values and standard deviations become small when aggregated to the grid scale (i.e., 0.5°). The T configuration better mimics the 1KM simulations with TOP than the D configuration and better captures the sub‐grid topographic effects on surface energy balance and boundary conditions. These results underline the importance of representing sub‐grid topographic heterogeneities in LSMs and motivate future research to understand the sub‐grid topographic effects on land‐atmosphere interactions over mountainous areas.

“…The model precipitation bias is larger than the difference between NH and H simulations (Figure 1d) in general. Both NH and H simulations have wet biases over the ITCZ, in particular near the Maritime Continent and western Pacific, which remains a persistent problem in high resolution climate models including HighResMIP (Bacmeister et al, 2014;Caldwell et al, 2019Caldwell et al, , 2021McClean et al, 2011;Roberts et al, 2019). NH does not exhibit better performance than its H counterpart from the global perspective at 28 km.…”

Section: Model Performancementioning

confidence: 89%

“…In this section, we focus specifically on the differences between the H and NH model. More details about SCREAM are provided in Caldwell et al (2021).…”

Section: Model Setupmentioning

confidence: 99%

“…While the horizontal grid spacing necessary for producing NH effects is generally around 10 km, recent studies have also been shown that the inclusion of moist physics can lead to significant divergence between H and NH models even around 36 km grid spacing (Gao et al, 2017;Yang et al, 2017). While this grid spacing is finer than the typical grid spacing for global climate models, recent pushes toward higher horizontal resolution in atmospheric models have placed us squarely in this regime (Caldwell et al, 2021;Haarsma et al, 2016;Stevens et al, 2019). Consequently, it is both important and timely to investigate NH effects in global climate modeling systems, particularly in the context of seasonal to climatological scale simulations.…”

mentioning

confidence: 99%

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An Assessment of Nonhydrostatic and Hydrostatic Dynamical Cores at Seasonal Time Scales in the Energy Exascale Earth System Model (E3SM)

Liu

Ullrich

Guba

et al. 2022

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The hydrostatic (H) approximation is widely used in numerical atmospheric models to simplify the underlying fluid equations and avoid the timestep restrictions imposed by vertically propagating waves (Saito et al., 2007;Salmon, 1988). Under this approximation the atmosphere is assumed to be continuously in hydrostatic equilibrium, with a balance between gravity and vertical pressure gradient; in essence, any hydrostatic imbalances are assumed to be corrected instantaneously. The hydrostatic approximation can be shown to be a reasonable assumption when the horizontal scale is much larger than the vertical scale. However, nonhydrostatic (NH) effects are crucial to the simulation of certain fine-scale phenomena, such as deep convection and flow over topography; in these circumstances, departures from hydrostatic equilibrium need to be taken into account. While the horizontal grid spacing necessary for producing NH effects is generally around 10 km, recent studies have also been shown that the inclusion of moist physics can lead to significant divergence between H and NH models even around 36 km grid spacing (Gao et al., 2017;Yang et al., 2017). While this grid spacing is finer than the typical grid spacing for global climate models, recent pushes toward higher horizontal resolution in atmospheric models have placed us squarely in this regime (Caldwell et al., 2021;Haarsma et al., 2016;Stevens et al., 2019). Consequently, it is both important and timely to investigate NH effects in global climate modeling systems, particularly in the context of seasonal to climatological scale simulations.