Elimination of spectral blocking by ensuring rotation-free property of discretised pressure gradient within a spectral semi-implicit semi-Lagrangian global atmospheric model

08/21/2019

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by   Masashi Ujiie, et al.

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The widely-adopted discretisation of the horizontal pressure gradient term formulated by Simmons and Burridge (1981) for atmospheric models on σ-p hybrid vertical coordinate is found to incur spectral blocking for rotational wind components at high vertical levels when used in a spectral semi-Lagrangian model run on a linear grid. A remedy to this issue is proposed and tested using a spectral semi-implicit semi-Lagrangian hydrostatic primitive equations model. The proposed method removes aliasing errors at high wavenumbers by ensuring that the rotation-free property of the pressure gradient term on isobaric surface, a feature possessed by the continuous system, is preserved in the discretised system, which highlights the significance of mimetic discretisation within the context of numerical weather prediction models.