Comparison between different SNOOPY runs of 2D MTI with whistler suppression and with different combinations of harmonic filtering of χ and hyperviscosity in θ: without harmonic filtering and without hyperviscosity (left), with filtering and without hyperviscosity (middle), and with both (right). The parameters of the runs are otherwise identical and the same as the run with α = 4 × 10⁻⁴. For visualization purposes we zoomed in on a region of size 200 × 200 cells (the resolution of the runs is 1024²). Only the run with both harmonic filtering and hyperviscosity shows no signs of Gibbs oscillations in either χ and the isothermality parameter σ, which depends on the gradient of θ.