江淮地区夏季雨量与北半球500hPa环流遥相关的不稳定性

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

用 5 0年 ( 1 95 1～ 2 0 0 0年 )观测资料 ,分成 1 95 1～ 1 976年和 1 977～ 2 0 0 0年两个时段 ,研究了江淮地区夏季 ( 6～ 8月 )雨量与北半球 5 0 0hPa季平均环流时滞遥相关的年代际变化 ,同时提出了遥相关不稳定指数 ,讨论了遥相关不稳定性的空间分布和季节变化。结果表明 ,这两个时段遥相关的空间分布存在显著差异 ,且前一时期时滞遥相关强度明显强于后一时期 ,特别是江淮地区夏季雨量与前期冬季西太平洋型 (WP)的相关仅在 1 976年以前显著 ,1 977年以后迅速减弱消失 ,而对于后一时期 ,与春季欧亚遥相关型 (EU)的相关明显加强。另外 ,后一时期江淮地区夏季雨量与夏季EAP波列的相关明显强于前一时期。它反映了太平洋年代际振荡 (PDO)对东亚季风降水和环流年际相关的影响 。

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 1951—1976 and 1977—2000. A teleconnection instability index is introducted, and the spatial and seasonal variations of the instability are discussed. Results show that the 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.