Abstract

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.

Highlights

  • Increasing resolution is generally regarded as an effective way to improve global weather and climate modeling (Jung et al, 2012; Wehner et al, 2014; Zhang et al, 2014; Yu et al, 2019)

  • The multiresolution approach is usually realized by an unstructured mesh model, such that a more flexible resolution choice can be achieved by considering multiple regions

  • A set of parameterization schemes from the Weather Research and Forecast (WRF) model (Powers et al, 2017). This package is being tuned for Global-toRegional Integrated forecast SysTem (GRIST)-NDC, which is targeted at simulating nonhydrostatic dynamics in a nonhydrostatic regime

Read more

Summary

Introduction

Increasing resolution is generally regarded as an effective way to improve global weather and climate modeling (Jung et al, 2012; Wehner et al, 2014; Zhang et al, 2014; Yu et al, 2019). The stretched grid (e.g., Hourdin et al, 2006; Harris et al, 2016) and multiresolution approaches (e.g., Ringler et al, 2011; Guba et al, 2014) are close in terms of their conforming style They maintain the global modeling configuration while permitting increased resolution for certain regions. Based on a VR configuration, the Community Atmosphere Model (CAM) with a spectral element core (Taylor, 2011) maintains tropical cyclones crossing the transition zone well without discernable wave reflection (Zarzycki et al, 2014) While these earlier studies have reported the benefits of VR modeling, a proper utilization of this technique is still challenging and deserves ongoing exploration.

Model framework and dynamics
Model physics
Time-step choices and explicit diffusion
Smagorinsky diffusion
Hyperdiffusion
Generation of the VR mesh
Generators
Density function
Single-region refinement
QU G7 QU G8 QU G6X4 G5B3X4 SURX4 G7X4 G8X4 G8X4L2 G7X4-polycentric
Multi-region refinement
Simple physics
QU G6X4L2
Full physics
Conclusions
On the overall performance
On the impact of explicit diffusion
On the impact of the mesh styles

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.