Mechanisms of two types of summer persistent extreme precipitation events in the northeastern Tibetan Plateau

The northeastern Tibetan Plateau (TP) features complex terrain, and persistent extreme precipitation events (PEPEs) are key factors inducing landslides and mudflows in the northeastern TP and its downstream regions. A comprehensive understanding of PEPEs mechanisms is crucial but remains insufficient. This study investigates PEPEs characteristics and underlying mechanisms over the northeastern TP from a synoptic perspective, by objectively classifying PEPEs into two distinct types. Type1 (thermally triggered) develops in anomalously warm and moist environments across the TP, accompanied by a localized quasi-stationary shallow trough over the northeastern TP. Convection is initiated by thermodynamic forcing, wherein latent heating dominantly increases the potential vorticity (PV) in the mid-lower troposphere, enhancing the trough and thereby precipitation. Type1 tends to develop more rapidly and persist longer compared with Type2. Type2 (dynamically forced) is closely associated with the quasi-barotropic cold trough in mid-high latitudes, developing in an overall anomalously cold and dry environment over the TP, with moisture concentrated merely in the northeast. Precipitation is triggered by intense dynamical forcing east of the trough. As the trough moves eastward, the intrusion of high-PV air from the upper troposphere enhances the cold trough through horizontal and vertical advection. The precipitation evolves along with the eastward movement of the deep trough, presenting steadier and temporally symmetrical variation relative to the peak time. The results provide knowledge about the evolution mechanisms of the two types of PEPEs in the northeastern TP triggered in different environments, favoring the PEPEs forecast and disaster prevention over the TP and downstream regions. • Two typical types are identified for summer PEPEs in the northeastern TP. • Type1, formed in warm-moist environments, is triggered by local thermal forcing. • Type2, associated with a moving cold trough, is driven by strong dynamical forcing.