Distinguish Extreme Precipitation Mechanisms Associated with Atmospheric River and Non-Atmospheric River in the Lower Yangtze River Basin

Abstract This study investigates the disparity in quantitative moisture contribution and synoptic-scale vertical motion in the lower reaches of the Yangtze River (LYRB) for different extreme precipitation (EP) types, which are categorized as EP associated with atmospheric river (AR&EP) or non-atmospheric river (non-AR&EP). To analyze moisture contribution, a backward tracking using the water accounting model-2layers is performed. In general, the remote moisture contribution is 9.7 times greater than the local contribution, with ocean contribution being 1.67 times stronger than land contribution. However, terrestrial and oceanic contributions obviously increase in the EP types, especially for oceanic contribution being double in magnitude. Notably, the West Pacific (WP) contribution emerges as the dominant differentia between the EP types, playing a crucial role in AR formation. By solving the quasi-geostrophic omega equation, the upper-level jet stream (ULJ) acts as the primary dynamic forcing for transverse vertical motion in AR&EP, while the baroclinic trough exhibits a relatively weaker influence. However, both systems have a nearly equal impact on vertical velocity in non-AR&EP. The enhanced shearwise elevation in the non-AR&EP type is the response of the stronger upper-level ridge over the Tibetan Plateau (TP), which induce enhanced Q-vector divergence pointing towards the LYRB. However, the main dynamic differences is location of ULJ, which serves as the trigger role although weak. Diabatic forcing proves to be the decisive factor for vertical motion development, the difference attributed to the released excessive latent heating with excess moisture contribution from the WP in AR&EP with enhanced precipitation.