El Niño–Related Variations of Rainfall Characteristics over East Asia

Variations of rainfall characteristics related to ENSO warm episodes are studied, focusing on areas of excessive winter rainfall over East Asia during the period 1998–2017. The TRMM 3B42 data shows an El Niño-related northeast-southwest oriented band of positive rainfall anomaly over East Asia, which is set as our “area of interest” for subsequent analyses of rainfall characteristics. Calculation of moist static energy budget based on reanalysis data displays a dominant contribution from the low-level horizontal advection of moist static energy into the area of interest, which is coincident with the presence of an anomalous anticyclone over the Philippines and South China Sea. Analyses of rainfall characteristics for the area of interest show that, except for the lightest rain, all rain rate spectrum exhibits increasing frequency during El Niño winters, and that the amount of percentage change magnifies with rain rate. Further analyses of moisture budget reveal that the increase in the frequency is mainly due to strengthened local vertical motion during El Niño winter. In the meanwhile, the intensity for moderate to heavy rainfall strengthens, with the magnitudes larger and signals more consistent among data sets for heavy to extreme rainfall. Results of moisture budget analyses reveal that the strengthened rainfall intensity is predominantly contributed from the vertical advection term, which is further attributable more to the strengthened vertical motion (dynamic contribution) than to the increased moisture (thermodynamic contribution) in the area of interest during El Niño winter.