阿留申低压低频变化及其相关的瞬变动力学过程分析

利用NCEP/NCAR 1979—2013年的再分析资料,研究了冬季阿留申低压低频变化的环流特征,探讨了阿留申低压低频变化形成和维持的相关天气尺度瞬变强迫机制。冬季阿留申低压的低频变化在850 h Pa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 h Pa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,有利于阿留申低压低频变化异常空间型的形成和维持。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°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。

Low-frequency variability of the Aleutian Low and its related synoptic transient eddy dynamic process

By using the NCEP/NCAR reanalysis daily dataset from 1979 to 2013, the circulation characteristics of the Aleutian Low on low-frequency scale in winter was investigated, moreover, the related synoptic transient eddy forcing mechanisms of the formation and maintenance of low-frequency variability of the Aleutian Low are also discussed. Results show that the low-frequency variability of the Aleutian Low in winter exhibits the evolution of an abnormal cyclone/anticyclone in the North Pacific basin area at 850 hPa, which means that the Aleutian Low on the low-frequency scale experiences strengthening, weakening and then returning to normal state process. It is the low-frequency cold center establishing in Northwest Pacific and gradually moving to the east that characterizes the temperature fields at 850 hPa. The analysis on the anomalous change of synoptic-scale transient eddy activities and transient eddy forcing shows that the transient eddy dynamic forcing anomalies becomes negative during the anomalous strengthening phase of the Aleutian Low, which is beneficial to establish and maintain the anomalous space type of the Aleutian Low on low-frequency scale. The anomalous fields of temperature tendency caused by the transient thermal forcing anomalies varies from positive value in the South Pacific of 40°N and to negative value in the North of 40°N in the middle of North Pacific, and the southern positive anomalies suppresses and weakens the expanding of low-frequency cold center to the south to a certain extent.