Independent perturbations for physics parametrization tendencies in a convection-permitting ensemble (pSPPT)

Abstract

Abstract. A modification of the widely used SPPT (Stochastically\nPerturbed Parametrisation Tendencies) scheme is proposed and tested in a\nConvection-permitting – Limited Area Ensemble Forecasting system (C-LAEF) developed at\nZAMG (Zentralanstalt fur Meteorologie und Geodynamik). The tendencies from four\nphysical parametrization schemes are perturbed: radiation, shallow convection,\nturbulence, and microphysics. Whereas in SPPT the total model tendencies are perturbed,\nin the present approach (pSPPT hereinafter) the partial tendencies of the physics\nparametrization schemes are sequentially perturbed. Thus, in pSPPT an interaction between\nthe uncertainties of the different physics parametrization schemes is sustained and a\nmore physically consistent relationship between the processes is kept. Two configurations\nof pSPPT are evaluated over two separate months (one in summer and another in winter).\nBoth schemes increase the stability of the model and lead to statistically significant\nimprovements in the probabilistic performance compared to a reference run without\nstochastic physics. An evaluation of selected test cases shows that the positive effect\nof stochastic physics is much more pronounced on days with high convective activity.\nSmall discrepancies in the humidity analysis can be dedicated to the use of a very simple\nsupersaturation adjustment. This and other adjustments are discussed to provide some\nsuggestions for future investigations.