冬季黑潮延伸体海区海洋锋强度变化及其与北太平洋风暴轴的关系

利用英国哈德莱中心（Hadley Center）1949~2014年表层海温资料，将黑潮延伸体海区海温经向梯度的大值区域的平均值定义为黑潮延伸体及其北部海洋锋强度指数（KEFI），利用数据分析方法研究了各季节KEFI的变化特征及其与北太平洋风暴轴的关系。分析表明，各季节的KEFI存在明显的年际和年代际变化特征，同时在冬季与北太平洋瞬时方差有显著正相关，两者在风暴轴主体位置的相关性最为显著，并且这种相关性在KEFI超前一个月时就所显现，同时对后期风暴轴也有一定影响，即冬季黑潮延伸体海区海洋锋的强度会影响风暴轴区域瞬时方差的变化。之后主要分析了这种影响的可能机制，发现在冬季KEFI高值年，由于海洋锋两侧的热量输送差异更加明显，导致海洋锋附近的近表面气温经向梯度增强，维持了近表面的斜压性，促进涡动热量的向极输送和海洋锋南侧的向上输送，有利于瞬时涡旋的发展。另外大尺度环流场与冬季黑潮延伸体海洋锋也有关系，具体表现为，在海洋锋强年，阿留申低压加深，副热带高压略有加强，对应的对流层低层位势高度场在40°N以北有负变高，以南有正变高，同时高空极锋急流加强，副热带西风急流减弱加宽北抬，海洋锋偏弱年的变化则相反。因此，冬季黑潮延伸体及其北部的海洋锋主要通过两侧海表热量输送差异不断产生气温梯度，进而维持斜压性以促进上层风暴轴的发展。

The Variability of the Oceanic Front in Kuroshio Extension and Its Relationship with the Pacific Storm Track in Winter

The intensity index of Kuroshio extension and its northern front zone (KEF) is defined as the area average of meridional SST (sea surface temperature) gradient by using Hadley Center''s surface sea temperature dataset (1949-2014), and the Kuroshio extension frontal intensity index (KEFI) has seasonal and 10 a interdecadal variations. In winter, the KEFI has a significant positive correlation with the transient variance in the North Pacific storm track area, and the positive relationship appears when KEFI leads the storm track by one month, which indicates that the intensity of KEF can influence the storm track in winter, and KEFI would influence the subsequent storm track. Further investigations on the possible mechanism reveal that when the winter SST front is stronger, a more significant difference between ocean-air heat fluxes on both sides of the KEF can strengthen the near-surface temperature gradient, which is favorable for the maintenance of the near-surface baroclincity and the transient heat transport and eventually promotes the development of transient eddies. Additionally, the large-scale circulation is also affected by the KEF in winter. When the KEF is strong, the Aleutian Low deepens and the subtropical high strengthens; 500 hPa potential height increases (decreases) in the south (north), and the subtropical jet becomes weak but wide. It is found that the oceanic front promotes the development of the storm track by transporting heat upward and maintaining the air temperature gradient in winter.