A Total Energy Error Analysis of Dynamical Cores and Physics‐Dynamics Coupling in the Community Atmosphere Model (CAM)

Lauritzen, P. H.; Williamson, David L.

doi:10.1029/2018ms001549

Cited by 17 publications

(26 citation statements)

References 28 publications

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“…Tracer mass conservation is analyzed in a pair of ne 30 pg 2 and ne 30 pg 3 aquaplanet simulations, following the method of Lauritzen and Williamson (). Energy and mass conservation due to a particular model process is assessed by model state I/O before and after each subprocess in the model.…”

Section: Resultsmentioning

confidence: 99%

Exploring a Lower‐Resolution Physics Grid in CAM‐SE‐CSLAM

Herrington

Lauritzen

Reed

et al. 2019

J Adv Model Earth Syst

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This paper describes the implementation of a coarser-resolution physics grid into the Community Atmosphere Model (CAM), containing 5 9 fewer grid columns than the dynamics grid. The dry dynamics is represented by the spectral element dynamical core, and tracer transport is computed using the Conservative Semi-Lagrangian Finite Volume Method (CAM-SE-CSLAM). Algorithms are presented that map fields between the dynamics and physics grids while maintaining numerical properties ideal for atmospheric simulations such as mass conservation and mixing ratio shape and linear-correlation preservation. The results of experiments using the lower-resolution physics grid are compared to the conventional method in which the physics and dynamical grids coincide. The lower-resolution physics grid provides a volume mean state to the physics computed from an equal sampling of the different types of nodal solutions arising in the spectral-element method and effectively mitigates grid imprinting in regions with steep topography. The impact of the coarser-resolution physics grid on the resolved scales of motion is analyzed in an aquaplanet configuration, across a range of dynamical core grid resolutions. The results suggest that the effective resolution of the model is not degraded through the use of a coarser-resolution physics grid. Since the physics makes up about half the computational cost of the conventional CAM-SE-CSLAM configuration, the coarser physics grid may allow for significant cost savings with little to no downside.

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Section: Resultsmentioning

confidence: 99%

Exploring a Lower‐Resolution Physics Grid in CAM‐SE‐CSLAM

Herrington

Lauritzen

Reed

et al. 2019

J Adv Model Earth Syst

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“…The dynamics time step is subcycled within a longer physics time step

Δ t_{phys}

, and the temperature and momentum increments from the physics are divided by the number of subcycles and added to the dynamical core at the beginning of each subcycle. The full moisture increment from the physics is applied only at the start of the first subcycle to conserve tracer mass ( ftype = 2 option in Lauritzen and Williamson, 2019).…”

Section: Methodsmentioning

confidence: 99%

On resolution sensitivity in the Community Atmosphere Model

Herrington

Reed

2020

Quart J Royal Meteoro Soc

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Advances in high-performance computing make it possible to run atmospheric general circulation models (AGCMs) over an increasingly wider range of grid resolutions, using either globally uniform or variable-resolution grids. In principle, this is an exciting opportunity to resolve atmospheric process and scales in a global model and in unprecedented detail, but in practice this grid flexibility is incompatible with the non-or weakly converging solutions with increasing horizontal resolution that have long characterized AGCMs. In the the Community Atmosphere Model (CAM), there are robust sensitivities to horizontal resolution that have persisted since the model was first introduced over thirty years ago; the atmosphere progressively dries and becomes less cloudy with resolution, and parametrized deep convective precipitation decreases at the expense of stratiform precipitation. This study documents a convergence experiment using CAM, version 6, and argues that a unifying cause, the sensitivity of resolved dynamical modes to native grid resolution, feeds back into other model components and explains these robust sensitivities to resolution. The increasing magnitudes of resolved vertical velocities with resolution are shown to fit an analytic scaling derived for the equations of motion at hydrostatic scales. This trend in vertical velocities results in an increase in resolved upward moisture fluxes at cloud base, balanced by an increase in stratiform precipitation rates with resolution. Compensating, greater magnitude subsiding motion with resolution has previously been shown to dry out the atmosphere and reduce cloud cover. Here, it is shown that both the increase in condensational heating from stratiform cloud formation and greater subsidence drying contribute to an increase in atmospheric stability with resolution, reducing the activity of parametrized convection. The impact of changing the vertical velocity field with native grid resolution cannot be ignored in any effort to recover convergent solutions in AGCMs, and, in particular, the development of scale-aware physical parametrizations.

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“…SCREAM inherited its energy fixer from CAM. As described in Lauritzen and Williamson (2019), this energy fixer corrects errors due to pressure work, time integration in the dynamical core, inconsistent formulations of equation of state, and other minor sources of non‐conservation. Historically, CAM and the atmospheric component of E3SM had used an incorrect formulation for energy.…”

Section: Model Descriptionmentioning

confidence: 99%

Convection‐Permitting Simulations With the E3SM Global Atmosphere Model

Caldwell

Terai

Hillman

et al. 2021

J Adv Model Earth Syst

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This paper describes the first implementation of the Δx = 3.25 km version of the Energy Exascale Earth System Model (E3SM) global atmosphere model and its behavior in a 40‐day prescribed‐sea‐surface‐temperature simulation (January 20 through February 28, 2020). This simulation was performed as part of the DYnamics of the Atmospheric general circulation Modeled On Non‐hydrostatic Domains (DYAMOND) Phase 2 model intercomparison. Effective resolution is found to be the horizontal dynamics grid resolution despite using a coarser grid for physical parameterizations. Despite this new model being in an immature and untuned state, moving to 3.25 km grid spacing solves several long‐standing problems with the E3SM model. In particular, Amazon precipitation is much more realistic, the frequency of light and heavy precipitation is improved, agreement between the simulated and observed diurnal cycle of tropical precipitation is excellent, and the vertical structure of tropical convection and coastal stratocumulus look good. In addition, the new model is able to capture the frequency and structure of important weather events (e.g., tropical cyclones, extratropical cyclones including atmospheric rivers, and cold air outbreaks). Interestingly, this model does not get rid of the erroneous southern branch of the intertropical convergence zone nor the tendency for strongest convection to occur over the Maritime Continent rather than the West Pacific, both of which are classic climate model biases. Several other problems with the simulation are identified, underscoring the fact that this model is a work in progress.

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A Total Energy Error Analysis of Dynamical Cores and Physics‐Dynamics Coupling in the Community Atmosphere Model (CAM)

Cited by 17 publications

References 28 publications

Exploring a Lower‐Resolution Physics Grid in CAM‐SE‐CSLAM

Exploring a Lower‐Resolution Physics Grid in CAM‐SE‐CSLAM

On resolution sensitivity in the Community Atmosphere Model

Convection‐Permitting Simulations With the E3SM Global Atmosphere Model

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