Tropical convection often organizes into larger-scale and longer-lived structures, such as mesoscale convective systems (MCSs) and tropical cyclones (TCs). Despite its importance, most existing metrics of convective organization over a certain domain focus on spatial clustering, offering limited insight into how convective activity is partitioned across sizes. In contrast, the size distribution directly reflects the hierarchical partitioning of convective activity, distinguishing regimes dominated by numerous small-scale systems from those governed by a few large, organized structures. Here, we propose the Hierarchical Organization Index (HOI), an information-theoretic metric that quantifies convective organization by treating the sizes of individual convective systems as a probability distribution and computing the system-level entropy. By combining HOI with a spatial clustering metric, we establish a dual-metric framework that characterizes convective organization from two complementary dimensions: size hierarchy and spatial clustering. We apply this framework to convective systems across models and observations. In simplified settings, the dual-metric framework outperforms single-scalar metrics, captures the distinct sensitivities of aquaplanet TC organization to warming and rotation, and effectively tracks the evolution of self-aggregation in radiative-convective equilibrium. In realistic settings, observational analysis demonstrates that TCs actively reorganize their surroundings by suppressing peripheral convection, leading to stronger hierarchical dominance alongside increased spacing among the remaining systems. These findings underscore that spatial clustering alone is insufficient to characterize convective organization. Incorporating size hierarchy enables a unified framework that captures both aspects of convective organization across models and observations.

对流组织,热带气旋