Simulating springtime extreme rainfall over Southern East Asia: unveiling the importance of synoptic-scale activities

Abstract

AbstractThis study investigates the influence of synoptic-scale activities on extreme precipitation during March–April–May (MAM) over Southern East Asia (SEA) using observational data and compares the results with the outputs from 20 Coupled Model Intercomparison Project phase 6 (CMIP6) historical runs. Observations show that SEA intense daily precipitation in MAM is linked to enhanced upper-level synoptic-scale waves; these disturbances are associated with significant anomalous temperature advection as well as moisture flux convergence, creating favorable conditions for extreme rainfall. Furthermore, it is found that a temperature advection index (TAI) can be utilized to characterize such synoptic-scale activities. Inspection of CMIP6 historical runs reveals that, among 20 models, 13 models perform well in accurately capturing the observed SEA rainfall pattern; such extreme events are also closely linked to TAI in the model environment. Overall, observed (simulated) results show that 78% (75%) of extreme events in the Yangtze River Basin–South Korea–south of Japan region can be attributed to positive TAI. Additionally, the related circulation anomalies such as the upper-level synoptic-scale wave feature, temperature advection, and moisture anomalies from these models closely resemble those observed during extreme precipitation days in SEA. Our findings suggest that TAI can effectively indicate both the frequency and intensity of extreme rainfall events in SEA, along with the associated synoptic-scale activities. Further study reveals a close lead-lag correlation between TAI and rainfall patterns over SEA. This correlation is characterized by eastward-propagating wave trains across the entire troposphere. Consequently, TAI not only acts as a benchmark for quantifying synoptic-scale extreme rainfall in SEA but also shows potential in predicting SEA rainfall linked to synoptic-scale disturbances.