华北降水年代际变化特征及相关的海气异常型

利用近50年华北地区26个站逐月降水观测资料和全球大气海洋分析资料，分析了华北降水的年代际变化特征及其和全球海气系统年代际变化的关系.对华北降水距平指数变化分析表明，近50年来华北降水具有减少的总体趋势，叠加在该趋势之上的是年代际变化，其中1965年和1980年发生了两次跃变，使得20世纪80年代干旱尤为严重.在对华北地区降水年代际变化特征分析的基础上，揭示了与华北降水年代际异常相伴随的大气环流和上层海洋热力异常型.结果表明，华北降水年代际异常与太平洋上层海洋热力状况异常有显著关系，主要表现为太平洋年代际振荡（PDO）与华北降水异常的相关.在年代际时间尺度上，华北干旱与上层海洋热力及大气环流异常的配置关系如下：当华北地区干旱时，则热带中东太平洋海温偏高，北太平洋中部海温偏低，即太平洋上主要表现为PDO暖位相，全球大部分地区（包括华北地区）气温偏高，青藏高原地区气温偏低，日本北部及东西伯利亚气压异常偏低，华北及其以南大片地区气压偏高，华北地区由异常西北风控制，不利于水汽向华北地区输送.

Decadal-to-interdecadal variability of precipitation in North China and associated atmospheric and oceanic anomaly patterns

This study investigates the decadal to interdecadal variability of precipitation in North China and associated atmospheric and oceanic anomaly patterns, with using records of precipitation at 26 stations over North China and global analysis data of ocean and atmosphere for the period 1951－1998 The variability of precipitation in North China over the past 50 years is characterized by the interdecadal oscillation with two regime shifts occurring in 1965 and 1980, especially resulting in a severe drought in the 1980s. The lag and simultaneous correlations between precipitation in North China and selected variables for the global ocean and atmosphere are computed on the decadal to interdecadal time scales (8 years and longer). Such correlations suggest a framework for the relationship of the precipitation anomaly in North China with the thermal anomalies in surrounding oceans and the regional atmospheric circulation anomalies. Under the framework, the Pacific inter Decadal Oscillation (PDO) plays an important role in occurrence of the decadal to interdecadal drought or flood in North China. During the drought period, the sea surface temperature anomaly is positive in the tropical eastern Pacific but negative in the extratropical North Pacific, indicating a warm PDO phase, and vice versa. Accompanying the warm PDO phase, the sea level pressure anomaly is negative over eastern Siberia and north of Japan but positive over most of Southern China, which generates an anomalous northwesterly over North China and reduces gain of the water vapor from oceans.