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

Abstract

AbstractThe widely‐adopted discretization of the horizontal pressure gradient term formulated by Simmons and Burridge 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 wave‐numbers by ensuring that the rotation‐free property of the pressure gradient term on the isobaric surface, a feature possessed by the continuous system, is preserved in the discretized system, which highlights the significance of mimetic discretization within the context of numerical weather prediction models.