A Toy Model for the Global Annual Number of Tropical Cyclones

The annual number of global tropical cyclones (TCs) has remained rather stable at ∼90 in the past decades, yet the underlying physics and mechanisms remain elusive. This study utilizes observational data to assess TC-environment interactions, such as atmospheric drying, stabilization, and oceanic cooling, which occur after TC passage and inhibit subsequent TC formation. Focused on the recovery of TC-induced hostile environment, we construct an idealized toy model incorporating the global main development region (MDR), recovery time and influencing radius. The model well captures the spatial and temporal characteristics of TC activity. Then we propose a new scaling of annual TC number, framed as a spatiotemporal packing problem determined by the total spatiotemporal area available for TC formation and the average area occupied by each TC. The recovery time is included as a new temporal constraint, and this scaling is validated by toy model simulations and offers insights into observations. Specifically, based on TC attributes in the current climate, the scaling yields an estimate of ∼100 TCs per year given a recovery time of 2–3 weeks. It also implies that a warming climate might lead to fewer TCs due to increased TC size and longer recovery times.