Symbiotic Relationship between Meiyu Rainfall and the Morphology of Meiyu Front
Abstract Observational evidences from a heavy precipitation event of the 2020 extreme Meiyu season are presented here to reveal a symbiotic relationship between Meiyu rainfall and the morphology of Meiyu front. The two influence each other through dynamical and thermodynamic feedbacks and evolve in a coherent way to generate cyclic behaviors. Specifically, an intense and band-shaped Meiyu front leads to symmetrical instability in the lower atmospheric layer and convective instability in the middle atmospheric layer, forming a rain band along the front. The Meiyu front and its associated instability subsequently weakens as a result of rainfall and the front is bent by the process of tilting frontolysis. Deep convective instability in the middle and lower layers develops in the warm-humid prefrontal area, and triggers isolated heavy rainfall replacing the original rain band south of the bent front. This warm sector precipitation then strengthens the front through tilting and diabatic heating frontogenesis. A stronger front recovers its initial band shape and the associated rainfall also resumes the form of rain band along the front. Analyses of potential energy associated with instability, water vapor convergence, and cross-frontal circulation are carried out to illustrate key processes of this Meiyu front-rainfall cycle. The implications of this symbiotic relationship for simulating and predicting extreme rainfall associated with Meiyu fronts are presented.