Model Spread in the Tropical Cyclone Frequency and Seed Propensity Index Across Global Warming and ENSO‐Like Perturbations

Abstract

AbstractThe future projection of tropical cyclone frequency is highly uncertain. Recent multi‐model studies showed that the model spread in tropical cyclones is correlated with the model spread in seeds, which are defined as convective weak vortices. However, it was unclear how the model spread is related to the large‐scale circulation. Here we apply a downscaling theory recently developed using aquaplanet experiments to explain the seed frequency across four global atmospheric models having different parameterizations of convection and resolutions. The seed frequency has a larger model spread in response to uniform warming than to CO2 doubling or El Niño/La Niña‐like sea surface temperature perturbations. Across all climate perturbations, the seed frequency is captured by the downscaling theory, expressed as a seed propensity index. The index highlights the connection between the tropical cyclone seeds and the climatological mean ascent pattern.