Preprints
https://doi.org/10.5194/gmd-2021-82
https://doi.org/10.5194/gmd-2021-82

Submitted as: development and technical paper 30 Apr 2021

Submitted as: development and technical paper | 30 Apr 2021

Review status: this preprint is currently under review for the journal GMD.

Topography based local spherical Voronoi grid refinement on classical and moist shallow-water finite volume models

Luan F. Santos and Pedro S. Peixoto Luan F. Santos and Pedro S. Peixoto
  • Instituto de Matemática e Estatística da Universidade de São Paulo, Rua do Matão, 1010 - Butantã, São Paulo - SP, 05508-090

Abstract. Locally refined grids for global atmospheric models are attractive since they are expected to provide an alternative to solve local phenomena without the requirement of a global high-resolution uniform grid, whose computational cost may be prohibitive. The Spherical Centroidal Voronoi Tesselations (SCVT), as used in the atmospheric Model for Prediction Across Scales (MPAS), allows a flexible way to build and work with local refinement. Alongside, the Andes Range plays a key role in the South American weather, but it is hard to capture its fine structure dynamics in global models. This paper describes how to generate SCVT grids that are locally refined in South America and that also capture the sharp topography of the Andes Range by defining a density function based on topography and smoothing techniques. We investigate the use of the mimetic finite volume scheme employed in the MPAS dynamical core on this grid considering the non-linear classic and moist shallow-water equations on the sphere. We show that the local refinement, even with very smooth transitions from different resolutions, generates spurious numerical inertia-gravity waves that may even numerically de-stabilize the model. In the moist shallow-water model, where physical processes such as precipitation and cloud formation are included, our results show that the local refinement may generate spurious rain that is not observed in uniform resolution SCVT grids. Fortunately, the spurious waves originate from small-scale grid-related numerical errors and therefore can be mitigated using small amounts of numerical diffusion. We show that, in some cases, the clouds are better represented in a variable resolution grid when compared to a respective uniform resolution grid with the same number of cells, while in other cases, grid effects can deteriorate the cloud and rain representation.

Luan F. Santos and Pedro S. Peixoto

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2021-82', Darren Engwirda, 24 May 2021
  • RC2: 'Comment on gmd-2021-82', Nicholas Kevlahan, 27 May 2021
  • RC3: 'Comment on gmd-2021-82', Anonymous Referee #3, 04 Jun 2021
  • AC1: 'Authors response on gmd-2021-82', Luan Santos, 22 Jul 2021

Luan F. Santos and Pedro S. Peixoto

Model code and software

Code repository for "Topography based local spherical Voronoi grid refinement on classical and moist shallow-water finite volume models" Pedro Peixoto and Luan Santos http://doi.org/10.5281/zenodo.4614571

Luan F. Santos and Pedro S. Peixoto

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Latest update: 17 Sep 2021
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Short summary
The Andes act as a wall in atmospheric flows and plays an important role in the weather of South America, being currently under-represented in weather and climate models. In this work, we propose grids that better capture the mountains and, using idealized dynamical models, study the effects caused by the use of such grids. While possibly improving forecasts for short periods, the grids introduce spurious numerical (non-physical) effects which can demand added caution of model developers.