Impacts of different perturbation methods on multiscale interactions between multisource perturbations for convection-permitting ensemble forecasting during SCMREX

This study investigates the impacts of different perturbation methods on the multiscale interactions between different-source perturbations and precipitation forecasting in convection-permitting short-term forecasts. Initial Condition (IC) and MOdel physics (MO) perturbations are applied to a convection-permitting ensemble prediction system (CPEPS) in southern China for the Southern China Monsoon Rainfall Experiment (SCMREX) in May 2014. The analysis presented in this study is based on 32 12-hr forecasts and builds upon perturbation methods explored in the previous work. Different perturbation methods show different multiscale characteristics especially for four factors: the meso-beta-scale saturation rates and saturation values for MO perturbations and the forecast-perturbation magnitudes and changes in convective activities relative to the control member for IC perturbations. All of these factors are closely associated with the occurrence of dispersion reduction due to adding MO perturbations to IC perturbations. Such factors can be changed to different degrees by modifying the initial magnitudes of IC perturbations and by combining various types of perturbation methods. The faster meso-beta-scale saturations and smaller meso-beta-scale saturation values for MO perturbations, as well as the larger forecast-perturbation magnitudes and larger enhancements of convective activities relative to the control member for IC perturbations boost the dispersion reduction. To improve precipitation forecasting, it is instructive to apply dispersion reduction to the design of perturbation methods for CPEPSs, where forecast errors have been overestimated by IC perturbations especially at smaller scales.