A Comparison of Mesh Refinement in the Global MPAS-A and WRF Models Using an Idealized Normal-Mode Baroclinic Wave Simulation

Abstract

Idealized normal-mode baroclinic wave simulations are conducted to examine the impact of continuous mesh refinement compared with stepwise changes in resolution using nested grids. The nested-grid results are produced using the Advanced Research Weather Research and Forecasting (WRF-ARW) Model, hereafter ARW, and the continuous refinement results are produced using the atmospheric component of the Model for Prediction Across Scales-Atmosphere (MPAS-A). For the nested domain simulations with the ARW, variants of both one-way and two-way nesting techniques are examined. Significant reflection and distortion of waves are evident in results using one-way nesting, with the error increasing with decreasing boundary-update frequency. With continuous updating of the boundary conditions in one-way and two-way nesting, wave distortion is still evident near the lateral boundaries but the distortion is much less than with infrequent boundary updates. The conformal Voronoi meshes in MPAS provide a much smoother transition between mesh resolutions. Variableresolution mesh MPAS-A simulations, using different transition zones between high-and low-resolution regions, are compared with the results from the ARW simulations. In the MPAS-A simulations, there is no significant reflection of gravity waves, suggesting that continuous mesh refinement can eliminate distortions that tend to occur along the boundaries of nested meshes.

Characteristics of gravity waves generated in the jet-front system in a baroclinic instability simulation

“…However, Park et al (2014) highlighted that nesting can induce spurious reflection and distortion of waves from lateral boundaries. In addition, PS07 noted that numerical artifacts can potentially be included in the nested fields of variables when the fields are transited from one domain to another.…”

The WASCAL high-resolution regional climate simulation ensemble for West Africa: concept, dissemination, assessment

“…Further, large uncertainties and errors are associated with the result of each model run as a consequence of imperfect initial conditions, the model being an imperfect abstraction of reality, and from numerical errors and artefacts accumulating in long-term simulations (for example, Laprise, 2003;Park et al, 2014).…”

“…This is problematic for long-term transient simulations associated with a large computational domain (Davies, 1983;Warner et al, 1997;Harris and 5 Durran, 2010;Park et al, 2014). The different approaches to address this issue that are discussed in the literature range from daily to weekly re-initialisation, sometimes even including soil conditions (Otte, 2008), to transient runs covering the entire period of interest (Giorgi et al, 2009;Dieng et al, 2017).…”

Towards convection-resolving, global atmospheric simulations with the Model for Prediction Across Scales (MPAS) v3.1: an extreme scaling experiment

“…Supplying lateral boundary conditions to nested models can cause severe problems, up to the point where the RCM solution becomes inconsistent with the forcing data (Davies, 1983;Warner et al, 1997;Harris and Durran, 2010;Park et al, 2014). Starting off as an initial-value problem, the RCM solution gradually becomes a boundary value problem, which from a mathematical point of view represents a fundamentally ill-posed boundary value problem (Staniforth, 1997;Laprise, 2003).…”

“…For a typical refinement ratio of 3, two-thirds of the spatial wave-number spectrum present in the fine mesh are absent in the coarse mesh (Park et al, 2014). This implies that (a) these features must be spunup for inflows into the higher-resolution domain, and that (b) these wave numbers are reflected at the domain boundary for outflows from the high-resolution domain to the coarser domain.…”