冬季黑潮延伸体区域海表温度锋对北太平洋风暴轴的影响

利用NOAA最优插值逐日海表温度资料和NCEP/NCAR的逐日大气再分析资料，分析了冬季黑潮延伸体区域海表温度锋的变化及其对北太平洋风暴轴的影响。结果表明，冬季黑潮延伸体区域海表温度锋强度和纬度位置既存在年际变化，也存在年代际变化，且强度和位置的变化是相互独立的。冬季黑潮延伸体区域海表温度锋强度的年际变化对北太平洋风暴轴没有显著的影响，而其年代际变化则对北太平洋风暴轴具有非常显著的影响，当冬季海表温度锋偏强时，大气斜压性在鄂霍次克海及阿拉斯加附近区域上空增强，而在海表温度锋下游至东太平洋区域上空显著减弱，平均有效位能向涡动有效位能的斜压能量转换在45°N以北的太平洋区域上空有所增多，而在30°-45°N的太平洋区域上空有所减少，涡动有效位能向涡动动能的斜压能量转换在35°N以北的西太平洋区域以及45°N以北的东太平洋区域都显著增加，而仅在其南部边缘存在东西带状的减弱区域，导致40°N以北海区北太平洋风暴轴增强，40°N以南海区北太平洋风暴轴减弱，冬季海表温度锋偏弱时则有与之相反的结果。冬季黑潮延伸体区域海表温度锋纬度位置的变化对北太平洋风暴轴也存在较显著的影响，当海表温度锋位置偏北时，在其下游45°N以南的太平洋区域上空大气斜压性减弱，45°N以南的中东太平洋区域上空区域平均有效位能向涡动有效位能、以及涡动有效位能向涡动动能的斜压能量转换都减少；而在45°N以北的太平洋区域上空大气斜压性增强，在阿拉斯加湾附近上空尤其显著，在黑潮延伸体区域附近以及45°N以北的中东太平洋上空平均有效位能向涡动有效位能、以及涡动有效位能向涡动动能的斜压能量转换都显著增加，导致北太平洋风暴轴在其气候平均态轴线两侧呈现北正南负的偶极子形态；海表温度锋位置偏南时则有与之相反的结果。冬季黑潮延伸体区域海表温度锋强度和位置的变化均对北太平洋风暴轴具有显著的影响，其具体的物理机制还需要进一步的研究。 

The variation of wintertime Kuroshio Extension SST front and its influence on the Pacific storm track

This paper analyzes the variation of wintertime Kuroshio Extension SST front and its influence on the Pacific storm track using NOAA daily Optimum Interpolation Sea Surface Temperature (SST) data and NCEP/NCAR daily atmospheric reanalysis data. Results show that the strength of wintertime Kuroshio Extension SST front has significant interannual to interdecadal variations,and mostly shows interdecadal variation. The interannual and interdecadal variations are independent of each other. The interdecadal variation of the strength of wintertime Kuroshio Extension SST front has significant influences on the Pacific storm track, but the interanual variation doesn''t. When the SST front is strong, the baroclinicity significantly decreases over the region from the downstream to the eastern Pacific, and increases over the Okhotsk Sea and the region near Alaska; the baroclinic energy transfer from the mean available potential energy to the eddy available potential energy (BCEC1) increases over the Pacific south of 45°N, and decreases over the Pacific between 35°-45°N; the baroclinic energy transfer from the eddy available potential energy to eddy kinetic energy (BCEC2) significantly increases over the western Pacific north of 35°N and eastern Pacific north of 45°N, and only decreases over the southern adjacent band region, resulting the strengthening of Pacific storm track over the Pacific north of 40°N and the weakening of Pacific storm track over the Pacific south of 40°N,and vice versa. When the position of SST front shifts northward, the baroclinicity over the Pacific south of 45°N weakens, while both BCEC1 and BCEC2 reduce over the central and eastern Pacific south of 45°N, resulting in weakening of the Pacific storm track over the Pacific south of 45°N. Meanwhile, the baroclinicity over the Pacific north of 45°N increases, especially over the region near the Gulf of Alaska. BCEC1 and BCEC2 both significantly increase over the Kuroshio extension and the central and eastern Pacific north of 45°N where the Pacific storm track finally strengthens, and vice versa. Both the strength and position variations of wintertime Kuroshio Extension SST front have significant influences on the Pacific storm track, and the physical mechanisms behind need to be further studied.