Existing studies of convection organization usually focuses on the initiation stage or mature mesoscale convective systems stages separately or using limited intermediate states. However, the intermediate process through which convective cells progressively develop into a coherent system remains poorly characterized since conventional observations and analyses lack explicit representation of cell-system evolution from a continuous evolutionary perspective. Understanding this stage is fundamental to revealing how organized convection emerges under complex topographic and mesoscale environments. To explicitly represent this previously overlooked stage, the onset of convection organization is defined as the continuous process by which multiple convective cells progressively establish coherent spatial and temporal organization before stable system formation. Based on the South China radar reflectivity mosaic dataset, a multi-layer online tracking algorithm is first developed to simultaneously track convective cells and systems. The resulting data structure preserves the continuous evolutionary connectivity among convective entities across multiple organizational levels by explicitly recording merge, split and cell–system association relationships. This connectivity-based algorithm enables the continuous reconstruction of the complete cell-to-system organization process, allowing the organization process itself, rather than isolated snapshots, to become an analyzable object. Based on this representation, a process-oriented analysis framework is developed to identify organization onset events, reconstruct the pre-system evolution of constituent convective cells, and evaluate the continuous evolution of cell-system organization. The framework is tested with samples and demonstrates the capability to reconstruct the evolution of constituent cells prior to stable system formation and to characterize different organization onset behaviors in South China. This study bridges the long-standing observational gap between convection initiation and mature organized convection, providing a quantitative framework for representing and investigating convective organization in South China and other regions.

Deep moist convection; Convective Storm; Feature tracking