Relationship between the East Asia Subtropical Westerly Jet Anomaly and Summer Precipitation over Eastern China

Interdecadal changes of the East Asia subtropical westerly jet(EASWJ) and the precipitation in July and August(JA) are examined by using the observational data at 738 stations and the NCEP/ NCAR reanalysis.The relationship between the location displacement of EASWJ and the precipitation anomalies over North China and the Yangtze River valley are also investigated.The results show that an anomaly pattern with more(or less) precipitation along the Yangtze River valley and less(or more) precipitation over North and South China occurs in eastern China,and this pattern changes at the end of 1970s.At the same time,the axis location of EASWJ displaces southward from the end of 1970s,leading to changes in water flux convergence in the lower troposphere and divergence in the upper troposphere and vertical circulation,as a result,precipitation anomaly pattern changes.Correlation analysis indicates that while the jet axis is abnormally southward,the westerly wind over the region of 25°～35°N intensifies, weakens over the region of 42°～50°N,and the precipitation in North China decreases and increases along the Yangtze river valley,and vice versa.With the southward displacement of the EASWJ axis from the end of 1970s,a trend of increase and decrease in summer precipitation over North China and the Yangtze River valley occurs.Comparisons of the differences of the water vapor flux convergence in the lower troposphere,divergence in the upper troposphere and the vertical circulation show that the water vapor flux convergence in the lower troposphere weakens from 1980s,water vapor supply decreases,vertical motion suppressed,leading to a decrease in the precipitation over the North China,and vice versa along the Yangtze River valley.