Recent Progress in Numerical Atmospheric Modeling in China

et al. 2020

Geosci. Model Dev.

Self Cite

Abstract. Targeting a long-term effort towards a variable-resolution (VR) global weather and climate model, this study systematically configures and evaluates an unstructured mesh atmospheric model based on the multiresolution approach. The model performance is examined from dry dynamics to simple physics and full physics scenarios. In the dry baroclinic wave test, the VR model reproduces comparable fine-scale structures in the refined regions as a fine-resolution quasi-uniform (QU) mesh model. The mesh transition zone does not adversely affect the wave pattern. Regional kinetic energy spectra show that the fine-scale resolving ability improves as the fine resolution increases. Compared to a QU counterpart that has equivalent degrees of freedom, the VR model tends to increase the global errors, but the errors can be reduced when the resolution of the coarse region is increased. The performance over the coarse region is generally close to that of a low-resolution QU counterpart. Two multi-region refinement approaches, the hierarchical and polycentric refinement modes, further validate the model performance under the multiresolution refinement. Activating hyperdiffusion for horizontal velocity is helpful with respect to VR modeling. An idealized tropical cyclone test is further used to examine its ability to resolve fine-scale structures. In the simple physics environment, the VR model can have the tropical cyclone stably pass the transition zone in various configurations. A series of sensitivity tests examines the model performance in a hierarchical refinement mode. The simulations exhibit consistency even when the VR mesh is slightly perturbed by one of the three parameters that control the density function. The tropical cyclone, starting from the second refinement region and passing through the inner transition zone, gets intensified and covers a smaller area in the refined regions. Such variations are consistent with the behavior that one may observe when uniformly refining the QU mesh. In the full physics environment with a highly variable mesh that reaches sub-10 km resolution, the VR model also produces a reasonable evolution for the tropical cyclone. The explicit diffusion shows its usefulness in terms of suppressing some unrealistic isolated-scale structures that are far away from the initial vortex and does not adversely affect the physically important object. The fine-scale structure is determined mainly by the fine-resolution area, although the systems may have larger differences before they move into the fine-resolution area. Altogether, this work demonstrates that the multiresolution configuration is a reliable and economic alternative to high-resolution global modeling. The adverse impact due to mesh transition and the coarse region can be controlled well.

Section: Introductionmentioning

confidence: 99%

Configuration and evaluation of a global unstructured mesh atmospheric model (GRIST-A20.9) based on the variable-resolution approach

Zhou

et al. 2020

Geosci. Model Dev.

Self Cite

“…With the rapid development of computer architectures, the use of the quasiuniform grid has become a popular strategy to escape from the pole problem that plagues the global models. A variety of such models have been developed or under ongoing development over the years (cf., Ullrich et al, 2017;Yu et al, 2019). Broadly speaking, an AGCM contains two major components, a dynamical core to solve the adiabatic resolved-scale fluid dynamics, and a physical parameterization suite for estimating the collaborative effects of the subgrid-scale dynamics and non-dynamical processes.…”

Section: Introductionmentioning

confidence: 99%

Using a single column model (SGRIST1.0) for connecting model physics and dynamics in the Global-to-Regional Integrated forecast SysTem (GRIST-A20.8)

Peng

et al. 2020

Preprint

Self Cite

Abstract. A single column model (SGRIST1.0) is developed as a tool for coupling a full-physics package (from Community Atmosphere Model, version 5 (CAM5)) to the Global-to-Regional Integrated forecast System (GRIST). In a two-step approach, the full-physics package is first isolated and coupled to SGRIST1.0 for reducing the uncertainties associated with model physics and assessing its behavior, then assimilated by the model dynamical framework. In the first step, SGRIST1.0 serves as a tool for evaluating the physical parameterization suite in the absence of 3D dynamics. Three single column model test cases, including the tropical deep convection, shallow convection, and stratocumulus, demonstrate that the parameterization suite mimics the behaviors in the observations and the reference model (SCAM) outputs. Cloud fraction, cloud liquid, and some other micro- and macro-physical variables are sensitive to the model time step, suggesting time-step dependency of the corresponding parameterization schemes. The second step couples the physics package to the 3D dynamical modeling system, and the verified parameterization suite works well in GRIST. Two physics-dynamics coupling strategies are examined and found to have a clear impact on the intensity of the simulated storm. The incremental operator splitting strategy (ptend_f1_f1), produces a weaker storm than the pure operator splitting strategy (ptend_f2_sudden). Comparing these two splitting approaches, the ptend_f2_sudden coupling strategy has higher large-step stability than the ptend_f1_f1 option, but the intensity of the simulated storm is substantially reduced by ptend_f2_sudden provided that the time step becomes quite large. Some detailed model configuration strategies are suggested when using the CAM5 parameterization suite in GRIST.

“…The global atmospheric model is an important tool for operational weather forecasting, climate prediction and research-oriented modelling. In recent years, with the continuous improvement of computing power of massively parallel computers, the global model is developed towards higher horizontal resolutions (e.g., Haarsma et al (2016); Yu et al (2019); Stevens et al (2019); Dueben et al (2020)). The unstructured grid (the semi-structured icosahedral grid and the generic Voronoi polygonal grid are considered in this study) is one of the major choices for these newly developed global models (e.g., Ullrich et al (2017)), mainly owing to their ability to allow general computational patterns and their flexibility to switch between uniform-mesh and variable-resolution (VR) modelling.…”

Section: Introductionmentioning

confidence: 99%

“…Global-to-Regional Integrated forecast SysTem). The GRIST framework is developed based on a hierarchical structure, from a shallow water model (Zhang (2018); Wang et al (2019)) to a layer-averaged 3D dry dynamical core (Zhang et al (2019)), and a more complete moist dynamical model that supports the incorporation of model physics (Zhang et al (2020)). To facilitate rapid iterative development, we have created a set of developer-friendly parallel computing toolkits to support efficient establishment of numerical modelling workflow from code development to data…”

Section: Introductionmentioning

confidence: 99%

Development and performance optimization of a parallel computing infrastructure for an unstructured-mesh modelling framework

Liu

et al. 2020

Preprint

Self Cite

Abstract. This paper describes the development and performance optimization of a parallel computing infrastructure for an unstructured-mesh global model (GRIST; Global-to-Regional Integrated forecast SysTem). The focus is on three major aspects that facilitate rapid iterative development, including parallel computing, index optimization and an efficient group I/O strategy. For parallel computing, the METIS tool is used for the partition of the global mesh, which is flexible and convenient for both the quasi-uniform and variable-resolution simulations. The scaling tests show that the partition method is efficient. To improve the cache efficiency, several mesh index reordering strategies are investigated to optimize the performance of the indirect addressing scheme used in the stencil calculations. The numerical results show that the indexing strategies are able to speed up the calculations, especially for running with a small number of processes. To overcome the bottleneck of poor I/O efficiency for the high-resolution or massively parallel simulations, a group parallel I/O method is implemented and proven to be of high efficiency in the numerical experiments. Altogether, these three aspects of the parallel computing toolkits are encapsulated in a few interfaces, which can be used for general parallel modelling on unstructured meshes.