张盛曦^1，， 任雪娟^2，*

（  1、南京大学大气科学学院 ；       2、南京大学大气科学学院；  ）

摘要： 利用NCEP/NCAR1979-2013年的再分析资料，研究了冬季北太平洋海盆地区低层大气环流低频变化的特征，探讨了以阿留申低压为代表的大气环流低频变化形成和维持的相关天气尺度瞬变强迫机制。冬季北太平洋海盆地区大气低频变化在850 hPa环流场上表现为北太平洋海盆区一个异常气旋/异常反气旋在局地强弱变化的过程，即阿留申低压在低频尺度上先异常增强/减弱随后逐渐恢复正常态的演变过程，850 hPa上大气温度低频变化表现为低频冷中心在西北太平洋建立并逐渐东移的过程。对天气尺度瞬变扰动活动及其强迫的异常进行分析表明，北太平洋海盆区上空的瞬变动力强迫在阿留申低压异常增强的时期为负异常，有利于北太平洋海盆区异常气旋形成和维持。由瞬变热力强迫异常引起的温度倾向异常场表现为北太平洋中部以40 o N为界南正-北负的空间分布，其南部正异常在一定程度上抑制和削弱了低频冷中心向南的扩张。
关键词： 大气低频变化；天气尺度瞬变扰动；瞬变动力强迫；瞬变热力强迫

Zhang Shengxi， Ren Xuejuan^*

（  School of Atmospheric Sciences,Nanjing University；  ）

Abstract： This study investigates the circulation characteristics of the atmospheric circulation variability on low-frequency scale during wintertime through the NCEP/NCAR reanalysis daily dataset from 1979 to 2013, and the production and maintenance mechanisms of the low-frequency variability are discussed which related to the synoptic transient eddy forcing. The results show that the low-frequency variability of the atmospheric circulation over North Pacific during wintertime exhibits the evolution of a cyclone/anticyclone in the North Pacific basin area at 850 hPa, revealing the changing process of the Aleutian Low on the low-frequency scale: it strengthens/weakens first then gradually restores to the normal state. By analyzing the anomalous change of synoptic-scale transient eddy activities and transient eddy forcing, this study comes to a conclusion that the transient eddy dynamic forcing anomalies show the negative values during the anomalous strengthening phase of the cyclone, providing a beneficial environment for the production and maintenance of the anomalous space form of the Aleutian Low on low-frequency scale. There is a mismatch between the anomalous fields of temperature tendencies caused by the transient thermal forcing anomalies and the anomalous fields of low-frequency temperature, thus the low-frequency temperature anomalies are suppressed and weakened to a certain extent.
Keywords： Low-frequency variability; Synoptic-scale transient eddy activity; eddy dynamic forcing; eddy heat forcing

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