How can the winter North Atlantic Oscillation influence the early summer precipitation in Northeast Asia: effect of the Arctic sea ice

The early summer (May-June) precipitation in Northeast Asia (NEA) accounts for about 25% of the annual total, which is important for the local agriculture production. The potential influencing factors and the related mechanisms of early summer NEA precipitation variability, however, are not fully understood. Our study suggests that a dipolar NEA precipitation anomaly pattern in May-June highly resembles the second leading mode of NEA early summer precipitation variability, can be induced by the winter North Atlantic Oscillation (NAO) through the capacitor effect of the Barents sea ice (BSI). Further analysis indicated that during negative NAO winter, anomalous northerlies controlling the Barents Sea tend to increase the local sea ice and reach its peak in spring. The BSI anomalies persist from spring to the following early summer generates the positive-negative-positive geopotential height anomalies occupying the Arctic, Kamchatka, and extra-tropical western Pacific. The southerlies on the west flank of the anomalous extra-tropical western Pacific anticyclone advect sufficient water vapor from the Pacific to southern NEA, concurrent with lower-troposphere convergence, leading to rich rainfall over Korea and southern Japan. In contrast, the lower-level divergence may reduce the precipitation over northern NEA. At last, a physical-based empirical model is established using the winter NAO index. It shows that the winter NAO provides a promising predictability source for this anomalous NEA dipolar precipitation pattern.

Automated summary

The study found that the early summer precipitation variability in Northeast Asia is not fully understood, but may be related to the North Atlantic Oscillation and the Barents Sea ice cover. During negative NAO winters, anomalous northerlies increase local sea ice, leading to geopotential height anomalies that result in rich rainfall in southern NEA. Conversely, there may be reduced precipitation in northern NEA due to lower-level divergence.