Precursors and Formation Mechanisms of Event-Based Extreme Precipitation during Springtime in Central-Eastern China

This study investigates the precursors and formation mechanisms of spring (April–May) event-based extreme precipitation (EEP) during 1961–2014 in central-eastern China. The EEP events during springtime are primarily characterized by extreme precipitation that occurs at the first half of an event. During early stages of spring EEP events, a Rossby wave grows over western Europe and the North Atlantic Ocean. The wave propagates eastward toward East Asia, exhibiting a circumglobal teleconnection (CGT) pattern. Astrong anticyclone related to the CGT pattern is formed over the islands of Japan in the upper troposphere, enhancing the divergence anomalies and bringing more water vapor anomalies from the Sea of Japan into central-eastern China. Meanwhile, the westerly jet jumps northward and anomalous southwesterly water vapor flux is significantly prevalent, both associated with the onset of the Bay of Bengal summer monsoon (BOBSM). When the anomalous southwesterly and northeasterly moisture fluxes into central-eastern China combine, strong convergence is formed, providing abundant water vapor for extreme precipitation. The moisture budget analysis further suggests that the dynamic processes associated with horizontal wind anomalies play a crucial role in the moisture convergence for the spring EEP events. The advection of zonal and meridional moisture is strongly related to the anomalous winds of the CGT waves and BOBSM, respectively; the horizontal thermodynamic processes related to specific humidity and vertical advection contribute much less. The results indicate the preceding signals in the midlatitudes and subtropics for the spring EEP events, enabling extreme precipitation forecasting and hydrological prediction.