Symbiotic Relationship between Mei-Yu Rainfall and the Morphology of Mei-Yu Front

Abstract

Observational evidence from a heavy precipitation event of the 2020 extreme mei-yu season is presented here to reveal a symbiotic relationship between mei-yu rainfall and the morphology of the mei-yu 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 mei-yu front leads to symmetrical instability in the lower atmospheric layer and convective instability in the middle atmospheric layer, forming a rainband along the front. The mei-yu front and its associated instability subsequently weaken 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 rainband 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 a rainband 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 mei-yu front–rainfall cycle. The implications of this symbiotic relationship for simulating and predicting extreme rainfall associated with mei-yu fronts are presented.