冬季北太平洋的温带气旋活动及其与前期秋季北极海冰的关系

Variability of Winter Extratropical Cyclone Activity in the North Pacific and Its Relationship with Previous Autumn Arctic Sea Ice

基于欧洲中期天气预报中心(ECMWF)的ERA_interim全球再分析数据集,利用客观算法识别和追踪温带气旋,分析了1979—2014年冬季(12月—次年2月)北太平洋(120°E^120°W,20°N^80°N)的温带气旋活动特征及其变化,探讨了冬季风暴路径与秋季北极海冰异常的关系。北太平洋温带气旋活动的气候态显示为自日本以东洋面至阿拉斯加湾北部的风暴路径。对30°N以北气旋活动频率异常的EOF分析显示其第一模态为太平洋气旋活动的南北向偶极子结构,表示风暴路径南北摆动的变化特征,且有向北偏移的趋势。第二模态的空间分布表现为40°N^60°N之间的大陆沿岸和太平洋洋面上呈相反的分布形势。时间系数的回归分析显示,冬季太平洋风暴路径的南北摆动与秋季(9—11月)东西伯利亚海-波弗特海海冰的异常显著相关。该海区秋季海冰减少导致冬季阿留申低压区呈高压异常,西风急流北移,45°N^75°N之间的大气斜压性增强而45°N以南大气斜压性减弱,从而使风暴路径向45°N以北偏移。

Based on the ERA interim reanalysis data of European Centre for Medium-Range Weather Forecasts(ECMWF)and the detection and tracking algorithm of extratropical cyclone,we analyzed the activity of extratropical cyclone in the North Pacific(120°E^120°W,20°N^80°N)during winter(December to February next year)and its variability.The relationship between winter storm track and autumn arctic sea ice anomalies are discussed.The climatology of the North Pacific extratropical cyclone activity is characterized by the storm track from the ocean of east of Japan to the northern gulf of Alaska.The EOF analysis of cyclone activity distribution north of 30°N shows that the first mode is characterized by a dipole structure in the north and south,indicating the south-north oscillation of storm track,and the storm track has a northward trend.The second mode is characterized by opposite distributions of coastal and the North Pacific between 40°N^60°N.The regression maps of time coefficients show a significant correlationbetween the south-north oscillation of winter storm track in the North Pacific and the sea ice anomalies in the east Siberian sea-Beaufort sea during autumn(September to November).The decline of sea ice in this region can lead to a anticyclone anomaly in Aleutian low area,a northward shift of westerly jet,and a strengthen of atmospheric baroclinicity between 45°N to 75°N and a weaken south of 45°N,resulting in the northward shift of storm track to the north of 45°N.