Abstract
Regional weather forecasting models like the Weather Research and Forecasting (WRF) model allow for nested domains to save computational effort and provide detailed results for mesoscale weather phenomena. The sudden resolution change by nesting may cause artefacts in the model results. On the contrary, the novel global Model for Prediction Across Scales (MPAS) runs on Voronoi meshes that allow for smooth resolution transition towards the desired high resolution in the region of interest. This minimises the resolution-related artefacts, while still saving computational effort. We evaluate the MPAS model over Europe focussing on three mesoscale weather events: a synoptic gale over the North Sea, a föhn effect in Switzerland, and a case of organised convection with hail over the Netherlands. We use four different MPAS meshes (60 km global refined to-3 km (60– 3 km), analogous 30–3 km, 15–3 km, global 3 km) and compare their results to routine observations and a WRF setup with a single domain of 3 km grid spacing. We also discuss the computational requirements for the different MPAS meshes and the operational WRF setup. In general, the MPAS 3 km and WRF model results correspond to the observations. However, a global model at 3 km resolution as a replacement for WRF is not feasible for operational use. More importantly, all variable-resolution meshes employed in this study show comparable skills in short-term forecasting within the high-resolution area at considerably lower computational costs.
Highlights
Many traditional numerical weather prediction (NWP) models, such as the Weather Research and Forecasting (WRF) model (Skamarock et al 2008), are Limited Area Models (LAMs), that require boundary conditions from larger scale models
This study evaluates WRF and Model for Prediction Across Scales (MPAS) for three case studies: a synoptic gale case over the North Sea, a föhn case in Switzerland, and a case of organised convection with hail in the Assessment of MPAS variable resolution simulations in the grey-zone of convection against
The MPAS runs show a good agreement with the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis regarding path and core pressure, comparable to the uniform MPAS 3 km run for the same initialisation 28_00
Summary
Many traditional numerical weather prediction (NWP) models, such as the Weather Research and Forecasting (WRF) model (Skamarock et al 2008), are Limited Area Models (LAMs), that require boundary conditions from larger scale models. The Model for Prediction Across Scales (MPAS) uses Voronoi tessellations to create irregular multigonal grid cells around grid points, to create a global irregular grid (Skamarock et al 2012) This allows smooth transitions from coarse to fine resolution, in contrast to nesting techniques of traditional regional models. MPAS does not need the usual grid transformation around the poles, which results in improved computational performance for global simulations compared to classic methods with a latitude-longitude grid with polar filters or spectral methods (Skamarock et al 2012) This requires certain parameterisation settings to be scale-aware, in particular for cumulus parameterisations. Both models use the MYNN 1.5 order TKE scheme (Nakanishi 2010)
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