阿留申低压四种环流指数的分析和比较

Analysis and comparison of four kinds of circulation indices of Aleutian Low

分析和比较了20世纪90年代以来不同学者提出的阿留申低压(AleutianLow,AL)四种强度指数(Ii,i=1,4)、两种中心位置指数(λi、φi,i=3、4)的时频特征及其与同期北半球太平洋海面温度、气温、降水的相关联系。结果表明:1)强度指数Ii、i=2,4演变特征最相似;20世纪70年代中期之前AL偏弱,之后AL偏强;近年来又出现AL偏弱趋势。因I1为5个月平均场中AL的强度指数,故它与Ii、i=2,4差别较大。2)两种中心位置指数地理分布区域(λc3,φc3)大于(λc4,φc4),这与平均时段长短及中心位置指数定义差别有关。λc4由偏西转向偏东较λc3提早约5a,它与Ii、i=2,4的一致性更好。3)在强ElNin～o事件中,AL加强、中心位置偏东,强LaNin～a事件则相反。强度指数I2、I4和位置指数λc4反映上述关系较好。4)AL偏强、偏东年,中纬北太平洋区域低温、少雨,北太平洋东北部至北美西北部气温偏高、降水偏多,而北美南部气温偏低、降水偏少;反之亦然。

The time-frequency characteristics of four intensity indices Ii（i=1,4）and two center position indices（λi,φi;i=3,4）of the Aleutian low（AL）proposed by different scholars since the 1990＇s are analyzed and compared in this paper,and their correlation relationships with the sea surface temperature（SST）of the Pacific Ocean,air temperature and precipitation in the Northern Hemisphere during the same period are investigated.The results show that evolutionary features of Ii（i=2,4）are mostly similar：the AL was weaker before the mid-1970＇s,then stronger,and becomes weaker again in recent years;larger differences existed between I1 and Ii（i=2,4）probably because I1 is defined according to the 5-month mean pressure field.The geographic distributive range of the appearance of the center position of the AL determined by（λc3,φc3）is larger than that by（λc4,φc4）,which might be caused by the differences in the length of average time period and the different definitions of the center position between them;and it is about 5-yr earlier for λc4 to turn from the negative position anomaly phase to the positive one than the time when λc3 did,and the tuning time of λc4 is also more consistent with the transition time of intensity indices Ii（i=2,4）.In strong EI Nio events,the AL strengthened with its center shifting eastward;and vice versa in La Nia events.In this respect,intensity indices I2 and I4 and position indices λc4 and λc3 are comparatively better.When the AL was stronger（＇i0）and lay eastward of its normal position（λ＇ci0）,it was colder and drier in the mid-latitude North Pacific region and the southern area of North America,but warmer and wetter in the northeast area of North Pacific,and vice versa.