A method for seeding and unseeding tropical cyclones in Earth system models using axisymmetric vortices

Abstract. The upscale influence of tropical cyclones (TCs) on the broader climate system remains poorly understood because of limitations in existing diagnostic and modeling methods. To address this, we present a method to modulate TC activity online in Earth-system models. Balanced, axisymmetric TC-like vortical perturbations derived from an analytical formulation with tunable parameters are superimposed on the atmospheric state. To add TCs to the model ("seeding"), cyclonic perturbations are introduced into quiescent environments. To remove TCs from the model ("unseeding"), anticyclonic perturbations are iteratively tuned to cancel existing TCs. During vortex insertion and removal, the balanced formulation prevents spurious wave generation while scalar global field corrections prevent climate drift.

In fully coupled aquaplanet simulations, the method reliably modulates TC climatology: seeding increases TC frequency and accumulated cyclone energy well above baseline, while unseeding reduces them by up to 95%. TC tracking shows that seeding primarily enhances genesis, whereas unseeding suppresses TC frequency by predominantly targeting incipient storms. The resulting experiments produce systematic tropical mean-state and radiative responses that scale approximately monotonically with TC activity, including upper-ocean cooling and mid-tropospheric drying as TC activity increases. These large-scale atmospheric mean-state responses differ qualitatively from short-term local anomalies associated with individual TCs, providing strong evidence that TCs modify their surrounding environment. These results establish online vortex manipulation as a practical, climatologically stable framework for investigations of TC upscale effects in the coupled tropical atmosphere-ocean system.