A New Organization Metric for Synoptic Scale Tropical Convective Aggregation

Abstract

Organization metrics were originally developed to measure how densely convective clouds are arranged at mesoscales. In this work, we apply organization metrics to describe tropical synoptic scale convective activity. Such activity is identified by cloud-precipitation (hybrid) regimes defined at 1-degree and 1-hourly resolution. Existing metrics were found to perform inadequately for such convective regime aggregates because the large domain size and co-existence of sparse aggregate occurrences with noisy isolated convection often violate assumptions inherent in these metrics. In order to capture these characteristics, the existing “convective organization potential” (COP) metric was modified so as to: (1) focus on local organization and (2) provide increased weight to aggregate size. The resulting “area-based COP” (ABCOP) is found to outperform existing metrics in tropical convective events at synoptic scales. Moreover, this new organization metric can match the performance of existing metrics, or arguably be better, over a wide range of domain sizes.