Interactions between Initial and Lateral Boundary Perturbations in Convection-Permitting Ensemble Prediction 

How to construct appropriate perturbations for convection-permitting ensemble prediction systems (CPEPSs) is a critical issue awaiting urgent solutions. As two common perturbations, initial perturbations (IPs) and lateral boundary perturbations (BPs) interact with each other, affecting the model error growth, especially in mesoscale models. Using the China Meteorological Administration (CMA) CPEPS, this study tries to elucidate how BPs interact with matched and mismatched initial IPs under varied large-scale weather conditions/ forcings. Seven groups of experiments were conducted for strong-forcing and weak-forcing weather regimes over southern China, three with single IPs, one with single BPs, and three with combined perturbations. It is found that the perturbation magnitudes were dominated by meso-α-scale components, and IPs under weak forcing exhibited more pronounced effects than under strong forcing; whereas BPs exerted more pronounced effects under strong forcing than weak forcing regimes. Furthermore, it takes longer (shorter) time for the model variables at high (low) levels to obtain more perturbation energy from BPs than from IPs. Morover, for precipitation and certain dynamic variables, IPs and BPs can mutually reinforce. The source of these perturbations, and their specific vertical levels, do not alter the extent of their interactions. Nevertheless, the weather regime and the scales of the perturbations influence the strength of their mutual reinforcement. In particular, the weak-forcing regimes exhibit a more pronounced reinforcing effect, and meso-α scale perturbations are more conducive to fostering interactions compared to meso-β scale ones. Ultimately, it is the perturbation magnitude inherent in the initial perturbation itself that has determined the interactions between IPs and BPs.