Interdecadal variations of East Asia monsoon and its relation with precipitation over North China

Abstract

Based on long-time observational datasets, the inter-decadal variations of East Asian summer monsoon (EASM) and summer precipitations over North China together with the relationship between them are investigated by using composite analysis and wavelet transform. Results show that both EASM and summer precipitations over North China have undergone considerable inter-decadal variations over the last 100 years. The Inter-decadal variation of EASM is characterized by four major strong-weak phases, including two strong EASM periods, that is, the period of 1900~1910 and that from the late 1930s to end of 1960s, as well as two weak EASM periods from late 1910s to the end of 1930s and after 1970s. Corresponding to the inter-decadal variation of EASM, three evident abrupt changes have taken place in 1905, 1948 and 1971 respectively. It has been found that the atmospheric anomalous patterns for strong EASM years are completely distinct from that in weak EASM periods. The inter-decadal variability has been found in the summer precipitations over North China as well. Summer precipitations in North China have gone through four major dry-damp periods, and richer (less) rain periods are in good agreements with strong (weak) EASM periods on inter-decadal scale. Further investigations suggest that summer precipitation anomalies over North China are closely related to the variations of EASM on inter-decadal scale. During stronger (weaker) EASM periods, summer SLP and 500hPa geopotential height both exhibit negative (positive) anomalies over East Asia, implying Indian Low deepens and West Pacific Subtropical High (WSPH) is north (south) than normal. As a result, the North China summer precipitation is richer (less). It is noted that the relationship between precipitation and EASM is changeable with time and also shows inter-decadal features.