Impact of Kuroshio Extension dipole mode variability on the North Pacific storm track

Abstract

An index of a large-scale Kuroshio Extension (KE) sea surface height dipole (KED) mode is constructed using satellite altimeter sea level anomaly observations from January 1993 to December 2015 based on previous work of the second author. It is found that the KED mode that undergoes a decadal variation from a negative phase (a positive-over-negative dipole, KED⁻) to a positive phase (a negative-over-positive dipole, KED⁺) can affect the variability of the oceanic SST front and the North Pacific storm track. The results show that the oceanic SST fronts in the north of the KE region and in the KE region — referred to as the NSST and KSST fronts, respectively — are closely correlated with the KED mode. In the NSST front region, the SST front is stronger for KED⁻ than for KED⁺, and the opposite is the case in the KSST region. It is further revealed that the decadal phase transition of the KED mode can change the location and strength of the North Pacific storm track, with the North Pacific storm track being slightly weaker and moving more northwards as a whole during the KED⁻ mode than during the KED⁺ mode. The westerly wind associated with the storm track on the downstream side of the KE region intensifies and shifts northwards under KED⁻ compared to KED⁺. Furthermore, the transition of the KED mode gives rise to changes in the North Pacific storm track by changing the NSST and KSST fronts and meridional heat flux.

摘要

利用1993年1月至2015年12月的海表面高度异常资料引入黑潮延伸体偶极子模态指数（KED模指数），发现KED模存在正位相（南正北负偶极子模态）和负位相（南负北正偶极子模态）之间的年代际变化，并对海洋锋和北太平洋风暴轴产生影响。研究结果显示，黑潮延伸体北侧海洋锋和延伸体海洋锋都与KED模存在很好的相关关系。在黑潮延伸体北侧海洋锋区域，KED负模态下海洋锋的强度增强，延伸体区域海洋锋则相反。另外在KED负模态下，风暴轴会减弱北移，与风暴轴有关的西风也在风暴轴下游区域北移。进一步分析得到KED模态的转换可以改变海洋锋的强度从而改变上空经向热量通量，进而影响风暴轴。

Keywords:

• Kuroshio Extension
• oceanic front
• North Pacific storm track

关键词:

• 黑潮延伸体
• 海洋锋
• 北太平洋风暴轴