Relationship between interdecadal variability of North China summer rainfall, East Asia summer monsoon, and atmospheric circulation anomaly

Abstract

Interdecadal features of summer rainfall in North China, East Asia summer monsoon (EASM) and the anomaly of general circulation were explored by using NCEP/NCAR reanalysis data and summer rainfall collected from 20 stations over North China. Results showed that the periods of summer rainfall in North China are not in agreement with those of EASM, interdecadal features are obvious, the former with notable periods of 8a and18a, with an abrupt change occurred in 1960s, the latter 18a and 28a, with abrupt change in 1970s. There is marked correlation between the summer precipitation of North China and EASM, strong/weak summer monsoon with more/less precipitation in North China .Weak EASM is an important factor of the rainfall decreasing, but not the only one, for general circulation anomaly is close related to the rainfall decrease. The decline of air temperature in Tibetan tableland and North China results in less low pressure here; lack of water vapor is another factor for the rainfall decreasing. The weakened southwest monsoon in East Asia leads to the fact that water vapor can't arrive in the region to the north of 30°N. As opposite to the 1950s', the EU teleconnection pattern of 1980s is of the character with Europe(+),Ural(-),and mid-Asia(+) at 500hPa, which means the Ural ridge and Baikal trough weakening, zonal circulation is not good for exchanging cold and warm air. As a result, the activity of cold and warm air and precipitation over North China reduced.