The western North Pacific subtropical high (WNPSH) is one of the most important factors affecting the summer climate over East Asia, bringing either torrential rain or scorching drought to the regions beneath its sway. However, a joint study recently published in Atmospheric and Oceanic Science Letters by researchers from Hohai University, Institute of Atmospheric Physics/Chinese Academy of Sciences, and Nanjing University of Information Science and Technology, China, identifies an exceptional region in East Asia—the East China Sea (ECS). The interannual variability of summer precipitation over this area shows no statistically significant linkage to the WNPSH.
It is well known that the East Asian subtropical rainy belt is typically situated along the northern flank of the WNPSH, stretching from the middle–lower reaches of the Yangtze River basin (YRB) eastward to southern Japan. Therefore, the interannual variability of this rainy belt is significantly affected by the zonal shift of the WNPSH. Despite the ECS being situated between the YRB and southern Japan, the WNPSH cannot induce precipitation anomalies over this area, implying that the ECS precipitation has its own uniqueness.
This study identifies the large-scale circulation anomalies responsible for the interannual variability in precipitation over the ECS. It is found that the local cyclonic anomaly in the lower troposphere plays an important role. It favors low-level convergence of moisture and upward motion, and thus promotes enhanced precipitation. Further results suggest that this cyclonic anomaly tilts northward with height and is favored by the southward shift of the upper-tropospheric westerly jet.
"These results highlight the spatial heterogeneity of variability of the East Asian subtropical rainy belt. A more comprehensive understanding of its interannual variability requires separate analyses for different regional segments", concludes the corresponding author, Dr. Xinyu Li.
