INSTABILITY OF INTERANNUAL TELECONNECTIONS BETWEEN THE SUMMER RAINFALL IN JIANGHUAI REGIONS AND THE 500 hPa CIRCULATION IN NORTHERN HEMISPHERE

The interdecadal variations of the interannual teleconnections between the summer rainfall in the Jianghuai regions and the 500 hPa height field anomalies over the Northern Hemisphere are studied based on both sets for two periods 1957-1976 and 1977-2000. A teleconnection instabitity index is introducted, and the spatial and seasonal variations of the instability are discussed. Results show that difference of the teleconnection spatial distributions for two periods is dominant, in which the intensity of lagged teleconnection is stronger for the former period than the latter. Correlation of WP pattern in winter with summer rainfall in Jianghuai regions shows a coherent region of strong correlation before 1976 and no region with statistically significant correlation thereafter, but the correlation with EU pattern in spring was stronger for the latter period, and in the summer the correlation of EAP wave train with the rainfall is more significant for the latter than the former. It is resulted from the effects of Pacific decadal oscillation (PDO) on the interannual relationships between the East Asian monsoon rainfall and the circulation. This instability of the teleconnections is closely related to the interaction between interannual and interdecadal variations.