北太平洋东部风暴轴的变化特征及其与大气环流和SST异常的关系

利用欧洲中期天气预报中心ECMWF(European Center for Medium-range Weather Forecast)逐日再分析资料(ERA40),通过经验正交函数(empirical orthogonal function,EOF)分解发现,冬季北太平洋东部风暴轴有着显著的年际变化特征:第一变化模态为在气候平均位置南北相反的偶极子变化型,第二变化模态为在气候平均位置处一致增强或减弱的变化型,第三变化模态为三极子的变化型。进一步的回归分析发现:当东部风暴轴南压(北抬)时,同期冬季是一种厄尔尼诺(拉尼娜)年海温异常空间分布型,中纬度北太平洋海区以及赤道中、东海区,冬季冷(暖)异常的洋面上是异常低压(高压),对流层中层是太平洋—北美型(Pacific-North American Pattern,PNA)遥相关的正(负)位相;当东部风暴轴增强(减弱)时,同期冬季黑潮区海温偏暖(偏冷),对流层中层表现为西太平洋型(West Pacific Pattern,WP)遥相关的正(负)位相;当东部风暴轴呈现西北—东南+-+(-+-)相间三极子的分布时,同期冬季巴布亚新几内亚附近海温异常偏暖(冷),夏威夷附近海温异常偏冷(暖),冬季冷(暖)异常的洋面上是异常低(高)压,对流层中层表现出类似PNA正(负)位相。EOF分解各模态所对应时间系数与阿留申低压(Aleutian Low,AL)指数、PNA指数、Nino3指数、WP指数、黑潮海温(Kuroshio Current,KC)指数之间存在显著的相关,这些证明了东部风暴轴与同期大气环流及SST异常之间的联系。

Characteristics of eastern storm track variations over the North Pacific and its relationship with the atmospheric circulation and SST anomaly

Based on the daily reanalysis data of European Center for Medium Weather Forecast(ERA-40) and the empirical orthogonal function(EOF) method,we find that the first mode depicts a meridional seesaw variation of the storm track,the second mode depicts the variation of the storm track against its climatological position and the third mode depicts a tri-polar oscillation.Further regression analysis shows that:When eastern storm track moves southward(northward),the sea surface temperature(SST) is of El Nino(La Nina) pattern,winter colder(warmer) sea surface is unusually low(high) upon the east and middle ocean tropic areas and middle-latitude North Pacific and middle troposphere is of positive(negative) Pacific-North American Pattern(PNA) teleconnection;when eastern storm track strengthens(weakens),SST of Kuroshio Current is warmer(colder) than usual,and middle troposphere is of positive(negative) West Pacific Pattern(WP) teleconnection;when eastern storm track presents the positive-negative-positive(negative-positive-negative) tri-polar oscillation from northwest to southeast,SST near Papua New Guinea is warmer(colder) than usual,SST near Hawaii is colder(warmer) than usual,colder(warmer) sea surface is unusually low(high),middle troposphere is positive(negative) similar to PNA Pacific-North American Pattern,teleconnection.All in all,time coefficients of different modes have significant correlation with the Aleutian Low(AL) index,PNA index,WP index,Nino3 index and the Kuroshio Current(KC) index respectively,which demonstrates the existence of the relationship between the east storm track and atmosphere as well as SST anomaly.