Abstract
Abstract. SL-AV (semi-Lagrangian, based on the absolute vorticity equation) is a global hydrostatic atmospheric model. Its latest version, SL-AV20, provides global operational medium-range weather forecast with 20 km resolution over Russia. The lower-resolution configurations of SL-AV20 are being tested for seasonal prediction and climate modeling. The article presents the model dynamical core. Its main features are a vorticity-divergence formulation at the unstaggered grid, high-order finite-difference approximations, semi-Lagrangian semi-implicit discretization and the reduced latitude–longitude grid with variable resolution in latitude. The accuracy of SL-AV20 numerical solutions using a reduced lat–lon grid and the variable resolution in latitude is tested with two idealized test cases. Accuracy and stability of SL-AV20 in the presence of the orography forcing are tested using the mountain-induced Rossby wave test case. The results of all three tests are in good agreement with other published model solutions. It is shown that the use of the reduced grid does not significantly affect the accuracy up to the 25 % reduction in the number of grid points with respect to the regular grid. Variable resolution in latitude allows us to improve the accuracy of a solution in the region of interest.
Highlights
Atmospheric general circulation models (AGCMs) are basic tools for weather forecasting from several days to seasons
SL-AV20 is the latest version of the hydrostatic AGCM developed at the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS) in cooperation with the Hydrometeorological Centre of Russia (HMCR)
The SL-AV20 dynamical core is developed by the coauthors, while the greater part of subgrid-scale parameterizations is adopted from the ALADIN/LACE model (Geleyn et al, 1994; Gerard et al, 2009)
Summary
Atmospheric general circulation models (AGCMs) are basic tools for weather forecasting from several days to seasons. All quasi-uniformly spaced grids proposed to date suffer from one or more of the following problems (as discussed in Staniforth and Thuburn, 2012): disbalance between vector and scalar degrees of freedom (grids with triangular or hexagonal/pentagonal cells), non-orthogonality of the underlying coordinate system (cubed-sphere), and overset regions or grid transition (Yin-Yang, cubed-sphere) These issues can degrade the accuracy of atmospheric circulation simulation, and cause grid imprinting and/or the occurrence of unphysical wave modes and some other problems. As shown in Tolstykh and Shashkin (2012), the accuracy problems of reduced grid computations reported by Williamson (2007) and Staniforth and Thuburn (2012) can be overcome with proper construction of this grid (Fadeev, 2013) and using high-order discretizations Another feature of SL-AV20 is the possibility of using variable resolution in latitude.
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