北太平洋风暴轴的变异特征及其与中纬度海气耦合关系分析

Storm track variations in the North Pacific in winter season and the coupled pattern with the midlatitude atmosphere-ocean system

本文使用欧洲ECMWF(ERA40)再分析资料,通过经验正交函数(Empirical Orthogonal Function,EOF)分解探讨了冬季北太平洋风暴轴的变异特征,使用回归分析得到了与风暴轴空间异常型相关的冬季大气平均流异常、表层海温(Sea Surface Temperature,SST)异常的空间耦合型.研究结果表明,冬季北太平洋风暴轴主要有两种空间异常型,第一种是风暴轴中东部明显北抬(南压),使得整个风暴轴向东北(东南)倾斜,与此同时,在中纬度北太平洋海区,冬季暖(冷)异常的洋面上是异常高压(低压),海气系统在垂直向表现为一种暖脊(冷槽)配置,在对流层中高层是太平洋-北美(Pacific-North American,PNA)型负(正)位相.第二种是风暴轴整体性加强(减弱)并偏北(南),此时,黑潮区海温异常偏暖(冷),低层阿留申低压和高空的西风急流略偏北(南),对流层中高层表现为西太平洋(Western Pacific,WP)型负(正)位相.风暴轴EOF分解的时间系数与阿留申低压指数、PNA指数、WP指数,以及与尼诺3区(NINO3)指数、黑潮海温指数间显著的相关性再次证实了在北太平洋中纬度地区存在着SST异常、风暴轴异常和大气平均流异常三者间的空间耦合型.

The storm track variations in the North Pacific in winter are investigated by using European ECMWF （ERA40） reanalysis data and the Empirical Orthogonal Function （EOF） method. The coupled patterns of the atmosphere mean flow anomaly and the sea surface temperature （SST） anomaly, related with the storm track variations are studied by the regression method. The results show that there are two main variation modes of the storm track in the North Pacific in winter. The first type is characterized by north （south） shift of the mid-east part of the storm track that connotes a northeastward （southeastward） reorientation of the track. The regression analysis shows that the warmer （colder） SSTA occurs in conjunction with anticyclonic anomalies above that cover the midlatitude North Pacific, （cold trough） pattern in the vertical （PNA） negative （positive） phase companying with the first mode of the storm track. Those are warm ridge for the atmosphere-ocean system. Meanwhile, it is Pacific-North American at the mid and high troposphere. The second type is the intensification （weakening） and northward （southward） shift of the whole storm track. It is associated with warmer （colder） SST in the Kuroshio Current, northward （southward） shift of the Aleutian Low at the low troposphere and westerly jet at the high troposphere, and Western Pacific （WP） negative （positive） phase at the mid-high troposphere. The time coefficients of EOF have significant correlation with Aleutian Low index, PNA index, WP index, Nino-3 index and the Kuroshio Current index, respectively, which demonstrate the existence of the coupling among the three selected fields.