Variations in the 30–60‐Day Intra‐Seasonal Variability of Spring Precipitation Over the Mid‐Low Reaches of the Yangtze River and the Possible Mechanism

Abstract The precipitation intra‐seasonal variability (ISV) has an important influence on extreme precipitation events, profoundly influencing agricultural activities over the mid‐low reaches of the Yangtze River (MLRYR). Spectrum analysis reveals the existence of 30–60‐day ISV in the MLRYR spring precipitation. The mechanism analysis indicates that, on the intra‐seasonal time scale, the MLRYR precipitation ISV is primarily driven by a wave train over the Eurasian continent. The wave train, with an anomalous anticyclone (cyclone) over the East European Plain and an anomalous cyclone (anticyclone) over Central Asia, could cause more (less) precipitation over the MLRYR. On the inter‐annual and inter‐decadal time scales, the precipitation ISV intensity is influenced by a meridional dipole pattern of the westerly jet stream (WJS) over the Eurasian continent. The positive WJS pattern facilitates the barotropic instability generation and 30–60‐day ISV growth over the East European Plain. Therefore, the ISV intensity of the pronounced wave train is enhanced and further intensifies the MLRYR spring precipitation ISV. In contrast, the negative WJS pattern is unfavorable for regional barotropic instability generation, and therefore the spring precipitation ISV intensity over the MLRYR would be weak. Further analysis shows that the underlying snow cover and soil temperature anomalies could have a contribution to forming the WJS dipole pattern through changing the meridional temperature gradient. The results of this study could deepen our understanding of the spring precipitation ISV over the MLRYR and the mechanisms.