The structural compactness of a tropical cyclone seed affects its persistence

<p>Tropical cyclones (TCs) are often generated from pre-existing 'seed' vortices. A seed with a higher persistence might have a higher chance to undergo TC genesis, albeit understanding the factors influencing seed persistence remains a challenge. This study proposes that the role of planetary Rossby wave drag is a key dynamical factor affecting seed vortex persistence. A novel parameter, termed "vortex structural compactness" (Cv), is introduced to characterize the weakening of the vortex's maximum wind speed (Vmax) by planetary Rossby wave drag, represented as the ratio of Vmax to the Rhines speed at the radius of maximum wind (Rmax). The relationship between Cv and the vortex weakening rate is investigated through barotropic β-plane experiments. The initial Cv of vortices is varied systematically by altering their initial Vmax and Rmax in idealized wind profile models. Real-world developing TC seed data are sampled from reanalysis datasets, providing diverse Cv values for each seed. The barotropic experiments reveal a strong dependence of vortex early-stage weakening rate on the initial Cv, particularly for initially compact (Cv>1) members. A comprehensive TC seed dataset is compiled using TempestExtremes to identify qualified tropical disturbances. The correlation between TC seeds' lifetime average Cv and their persistence is examined, and large-scale low-level vorticity budget analysis is employed to investigate the relationship between TC seeds' Cv and maximum vorticity tendency.</p>