冬季北太平洋风暴轴的年代际变化特征及其可能影响机制

利用1958-2002年的ERA-40再分析资料,用谐波变换和EOF方法分析了冬季北太平洋风暴轴在年代际时间尺度上的变化特征,并通过回归分析的方法初步探讨了风暴轴年代际变化的可能影响机制.结果表明,在年代际时间尺度上,北太平洋风暴轴有两种主要模态,第1模态是风暴轴在其气候平均位置增强或减弱的主体一致变化型,其年代际变化受到上游涡旋强迫的影响,北大西洋强(弱)的涡旋活动,使得冬季北太平洋西风急流减弱(增强)、变宽(窄)、北抬(南压),同期北太平洋风暴轴活动偏强(弱),黑潮延续体区海表温度有偏暖(冷)的响应;第2模态是风暴轴中东部在气候平均位置南北两侧振荡的经向异常型,与太平洋年代际振荡(PDO)循环的暖(冷)位相相联系,下垫面海温非绝热加热的作用,激发加强(减弱)大气中类太平洋/北美遥相关型(PNA)的响应,引起大气斜压性异常偏南(北),使得风暴轴整体南压(北抬),且中东部向东南(北)方向移动.因此,冬季北太平洋风暴轴的年代际变化不仅是局地波-流相互作用的结果,还应考虑上游涡旋活动和海温热力强迫的作用.

Inter decadal variation characteristics of winter North Pacific storm tracks and its possible influencing mechanism.

The temporal and spatial characteristics of winter storm tracks in the North Pacific are analyzed on the inter decadal scale by using harmonious wave analysis and EOF analysis method based on the ERA 40 data (1958-2002). The influencing mechanism is also discussed through regression analysis with atmospheric circulation and sea surface temperature anomalies as a regressor. The results show that there are two main inter decadal scale variation modes of the storm tracks in the North Pacific during winter. The first mode depicts the variation of storm track against its climatological position, relating to the impact of the remote eddy forcing anomaly over the Atlantic area. The stronger (weaker) Atlantic eddy activity may cause the winter North Pacific westerly jet to become weaker (stronger), broader (narrower) and more northward (southward) and thus cause stronger (weaker) Pacific storm activities as well as a response of local warmer (cooler) SST over the Kuroshio current extension. The second mode depicts a meridional seesaw variation over the storm track, which is associated with the influence of the Pacific Decadal Oscillation (PDO) modes. The surface diabetic heat forcing may enhance (reduce) the PNA like teleconnection pattern response in 500 hPa height field, cause more baroclinicity abnormally to the south (north), and thus lead the storm track to wholly shifting southard (northward) with its eastern part to migrating to a southern location so that the track appears sloping toward the southeast (northeast). Therefore, the Pacific storm track variations on the inter decadal scale are not only caused by the local eddy zonal mean flow interaction, but also by the remote eddy forcing and diabetic heating effect of SST.