东北初夏极端低温事件的空间分布特征及其成因机理分析

采用东北三省150个测站1961~2008年的逐日温度资料和同期美国环境预报中心(NCEP)、国家大气研究中心(NCAR)2.5°×2.5°分辨率的全球再分析资料,探讨东北三省初夏极端低温事件的空间分布及其大气动力学特征,结果表明:该区初夏气温与夏季气温变化在时空尺度上相关显著,具有重要的预警作用;给出初夏极端低温事件的定义,其空间分布可归为3种类型,随纬度的增加极端低温事件发生的频率也显著增加;20世纪90年代以来,极端低温事件明显减少,仅出现2次,但影响范围遍布东北三省全境;阻高与冷涡的配置和大气低频Rossby波扰动对初夏东北冷涡活动气候基本流的同位相强迫,更增强了500 hPa位势高度距平场由北向南的"+、-"局域环流的异常,是极端低温事件的强弱与空间范围大小的重要动力机制;较为偏东的鄂霍次克海阻高和冷涡,以及冷平流的作用与以黑龙江省(包括吉林省的一部分)为主出现极端低温Ⅰ、Ⅱ类事件的关系更加密切,贝加尔湖阻高和鄂霍次克海阻高与偏南的强冷涡相互匹配、大气低频Rossby波扰动很强易出现第Ⅲ类极端低温事件。

Distribution of Extreme Cool Events over Northeast China in Early Summer and the Related Dynamical Processes

In this study,the spatial distribution and dynamic characteristics of extreme cool summer events in Northeast China were investigated.It unveiled that: the temperature variation of early summer could be used as a predictor to herald that of the whole summer in Northeast China.The extreme cool summer event was defined in this paper and it was divided into three kinds.Apparently,with the increasing latitude in Northeast China,the frequency of cool event increased too.Since 1990s,there only two cool events happened,but it could sweep over the whole region of Northeast China.The influence scope of cool event was closely related with the position and arrangement of cold vortex and blocking high.On climate mean state,the blocking high dominated over north of Northeast Asian and cold vortex governed over south of Northeast Asian at 500 hPa level,while the low-frequency Rossby wave disturbance,on the same phase,acted on the climate state,enhanced the dipole of "+,-"wave train,which was the significant dynamic mechanism that affected the strength and scope of unusually cool summer events.Additionally,owing to the effect of cold vortex and blocking high in the district of Okhotsk further east,the first and second types cool events more easily occurred in Heilongjiang Province,and part of Jilin Province.Blocking high in Baikal and Okhotsk area matched very well,in addition,cold vortex further south and Rossby wave strongly disturbed,were all benefit for the third kind type cool event occurrence.