Case Dependence of Multiscale Interactions between Multisource Perturbations for Convection-Permitting Ensemble Forecasting during SCMREX

Abstract

This study examines the case dependence of the multiscale characteristics of initial condition (IC) and model physics (MO) perturbations and their interactions in a convection-permitting ensemble prediction system (CPEPS), focusing on the 12-h forecasts of precipitation perturbation energy. The case dependence of forecast performances of various ensemble configurations is also examined to gain guidance for CPEPS design. Heavy-rainfall cases over Southern China during the Southern China Monsoon Rainfall Experiment (SCMREX) in May 2014 were discriminated between the strongly and weakly forced events in terms of synoptic-scale forcing, each of which included 10 cases. In the cases with weaker forcing, MO perturbations showed larger influences while the enhancements of convective activities relative to the control member due to IC perturbations were less evident, leading to smaller dispersion reduction due to adding MO perturbations to IC perturbations. Such dispersion reduction was more sensitive to IC and MO perturbation methods in the weakly and strongly forced cases, respectively. The dispersion reduction improved the probabilistic forecasts of precipitation, with more evident improvements in the cases with weaker forcing. To improve the benefits of dispersion reduction in forecasts, it is instructive to elaborately consider the case dependence of dispersion reduction, especially the various sensitivities of dispersion reduction to different-source perturbation methods in various cases, in CPEPS design.

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

“…13-24 hr). Moreover, the multiscale characteristics of IC/MO perturbations and dispersion reduction/enhancement have been confirmed by Zhang (2021) to be different in cases with different synoptic-scale forcings. Thus, it is still unclear if the impacts of the dispersion-reducing factors explored here on the multiscale interactions between IC and MO perturbations are valid for cases in other experimental periods.…”

Growth and Interactions of Multi-Source Perturbations in Convection-Allowing Ensemble Forecasts

“…Both the IC and LBC perturbations adopted the dynamic downscaling (DOWN) method. In this method, the analysis perturbations were added and interpolated into the inner and outer domains at the beginning of the forecast to imitate the IC and LBC uncertainties (Zhuang et al [66] ; Zhang [67] ). The LBC perturbations of the inner domain were provided by the forecasts of the outer domain.…”