Interannual variability of the summer precipitation over the East China Sea

It is well-known that the East Asian subtropical rainy belt, stretching from the middle–lower reaches of the Yangtze River basin eastward to southern Japan, is modulated by the zonal shift of the western North Pacific subtropical high (WNPSH). However, this study found that the interannual variability of precipitation over the East China Sea (ECS), a region between the Yangtze River basin and southern Japan, is not significantly affected by the WNPSH. Instead, large-scale circulation anomalies that favor enhanced precipitation over the ECS manifest as a local cyclonic anomaly in the lower troposphere, which promotes lower-tropospheric convergence and thus favors upward motion and enhanced precipitation. The lower-tropospheric cyclonic anomaly is favored by an extratropical cyclonic anomaly over Northeast Asia in the upper troposphere, in association with the southward shift of the East Asian westerly jet. These vertically aligned anomalies exhibit a northward tilt with height, suggesting that the precipitation over the ECS is primarily driven by extratropical circulation anomalies. Further results suggest that the local cyclonic anomaly tends to concur with a wave train over the North Pacific. These results contrast sharply with other segments of the rainy belt that are greatly affected by the zonal shift of the WNPSH. 夏季东亚副热带雨带从长江中下游地区向日本南部延伸, 显著受到西太平洋副热带高压(副高)纬向变动的影响.然而, 本研究发现, 位于长江中下游和日本南部之间的东海地区, 其降水的年际变化并未受到副高的显著影响.影响东海降水的大尺度环流表现为对流层低层的局地气旋异常, 该气旋异常随高度向北倾向, 并受到高空西风急流经向偏移的调控, 说明东海降水的年际变化主要与热带外环流有关.此外, 该气旋异常还常常与北太平洋的一支波列同时出现.