Abstract:

Using global atmospheric reanalysis data from the National Centers for Environmental Prediction/Department of Energy (NCEP/DOE) and the Global Precipitation Climatology Project (GPCP) for the period 1979–2021. By integrating the East Asian Summer Subtropical Westerly Jet Index (EAJI) and the Northeast Low Pressure index (NEALI), this study analyzed the characteristics of their distinct configurations on the interannual scale as well as the associated atmospheric anomalous conditions,further explored the synergistic effects of different circulation systems of the east Asian monsoon on climate change in east Asia and summer precipitation in China. The results showed that the variability in the intensity of Northeast Low Pressure and the displacement of the East Asian Westerly Jet were not independent. When both systems were in phase (either positive or negative), significant anomalous wave patterns appeared in the middle troposphere over the mid–to–high latitudes of Eurasia. Geopotential height anomalies were observed at 850hPa, with positive (negative) anomalies near the Ural mountains and negative (positive) anomalies east of Baikal lake. At 500hPa, geopotential height anomalies showed a positive–negative–positive (negative–positive–negative) pattern from the Ural mountains to Baikal lake and Japan. The jet shifted northward (southward), causing a slight northward (southward) movement of the subtropical high, leading to below–average (above–average) summer precipitation in southern China and along the Yangtze river, with above–average (below–average) precipitation in coastal southern China and northeast China. When the two systems were in an out–of–phase configuration, the spatial distribution of atmospheric circulation and precipitation anomalies was similar to that of the in–phase years, but the intensity of the climate anomalies over east Asia was significantly weaker.

Key words: Northern east Asian low, East Asian summer subtropical westerly jet, Coupling configuration, Summer precipitation