The Northern Hemisphere circumpolar vortex indices (size, strength and centre position) were defined and calculated by using the NCEP/NCAR data at the 500 hpa geopotential height field from 1958 -2006 with the Northern Hemisphere polar vorticity characteristic grade. According to these results, the Artic vortex indices at the 500 hPa level on the interaseasonal and interannual variation were compared and analyzed , getting some laws about the Northern Hemisphere polar vortex variation: the size of Artic vorticity has obvious interannual variation at 500 hPa geopotential height field. From the long-term trend, we discovered that the size had displayed contraction evidently from 1958 to 2006; the size and strength had marked interaseasonal variation, moreover they existed positive relationship to a certain extent.%运用NCEP/NCAR1958～2006年的500hPa月平均再分析高度场资料,结合500hPa北极极涡的特征等直线对北极极涡环流指数(面积、强度、中心位置)进行了计算.根据所得的计算结果比较分析了500hPa北极极涡环流指数的年际及季节变化,得到了一些北极极涡系统的变化规律:冬季500hPa北极极涡面积有明显的年际变化.从长期趋势来看,1958～2006年极涡面积呈现出显著减小的趋势；500hPa北极极涡的面积和强度存在明显的季节变化,并且两者之间有一定的正相关性.
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