The importance of low-deformation vorticity in tropical cyclone formation

摘要: Abstract. Studies of tropical cyclone (TC) formation from waves have shown that TC requires a wave-relative quasi-closed circulation: the "marsupial pouch" concept. This results in layerwise nearly contained region atmosphere which modification moisture, temperature and vorticity profiles by convective boundary layer processes occurs undisturbed. The pouch concept is further developed this paper. TCs develop near centre where flow solid body rotation. A reference-frame independent parameter introduced effectively measures level solid-body rotation lower troposphere. product normalized Okubo-Weiss absolute (OWZ). Using 20 yr ERA-interim reanalysis data IBTrACS global database, it 95% including, but not limited to, those forming are associated with enhanced levels OWZ on both 850 500 hPa pressure at time declaration, while 90% show for least 24 h prior to declaration. result prompts question whether extends beyond wave-type all formations world-wide. Combining low vertical shear requirement troposphere relative humidity thresholds, an imminent genesis defined. includes only relatively large-scale fluid properties resolved coarse grid model (>150 km), means can be used as detector climate applications. It also useful cyclogenesis diagnostic higher resolution models such real-time forecast models.