AN ABRUPT CHANGE IN THE INTENSITY OF THE EAST ASIAN SUMMER MONSOON INDEX AND ITS RELATIONSHIP WITH TEMPERATURE AND PRECIPITATION OVER EAST CHINA

Abstract

In this study, an East Asian summer monsoon intensity index is defined and the summer monthly indices of the East Asian monsoon are calculated for the period 1873–1989. Studies of the climate change of the index indicate that around 1918 the East Asian monsoon experienced an abrupt change, from weak to strong. This abrupt change occurred synchronously with that of the Northern Hemisphere air temperature. Studies of the relation of this East Asian summer monsoon index to the rainfall and temperature over China by using the data for the recent 40 years shows that when a strong monsoon occurs, China will experience an extensive high temperature in summer. The relationship between the East Asian summer monsoon and China's summer rainfall manifests itself on the north–south position of the rain belt. The position of the summer belt is northward when the monsoon is strong and southward when the monsoon is weak. Wet years over the middle and lower reaches of Chingjiang River are related to a weak monsoon whereas with a strong summer monsoon, dry years are often observed.