Implementing the HYbrid MAss flux Convection Scheme (HYMACS) in ICON – First idealized tests and adaptions to the dynamical core for local mass sources

Abstract

AbstractIn this study, the Hybrid MAss flux Convection Scheme (HYMACS) is implemented in the ICOsahedral Non‐hydrostatic (ICON) weather prediction model. In contrast to conventional convection parametrization schemes, the convective up‐ and downdraughts are solely treated as subgrid‐scale processes in HYMACS, whereas the environmental subsidence is passed to the grid‐scale dynamics of the hosting model. It is shown that the operational anisotropic divergence damping in ICON distorts the grid‐scale dynamical response on the net mass transport parametrized by HYMACS. Thus, a revised numerical filter configuration is developed which focuses on both the compatibility to local mass sources (sinks) and the effective suppression of numerical modes inherent from the model's triangular grid. Evaluation of Jablonowski–Williamson dynamical core experiments reveal that the combination of an isotropic second‐order divergence damping with a modified version of the fourth‐order divergence damping outperforms against numerical filters based on diffusion. The obtained results are similar to the operational set‐up indicating just a minor effect on the properties of the dynamical core. Moreover, a series of dry mass lifting experiments with the revised numerical filter confirms its compatability with HYMACS. The distortion of the grid‐scale circulation is removed while gravity waves are still retained despite the potentially degenerative effect of the fourth‐order divergence damping. Analyses of kinetic energy spectra confirm the effective suppression of checkerboard noise for a wide range of different situations. The present study may be understood as a base for future applications of HYMACS with a full cloud model in real‐case studies.