中文摘要：

利用NCEP／NCAR1949-2002年月平均再分析高度场资料，通过线性倾向估计、二项式系数加权平均、Morlet小波分析等诊断方法，系统地讨论了300hPa北半球极涡面积、强度及中心位置的年际和年代际变化特征，结果表明：（1）年平均北极涡的面积在20世纪70年代中期之前在总的上升趋势中有几次较小的波动，之后在总体下降趋势中有几次较大的起伏；Ⅰ、Ⅱ区的线性变化趋势非常小，Ⅳ区最大，夏季的年际变化相对明显一些，秋季变化最弱，各季节均有线性收缩趋势，冬季幅度最大，秋季最小。（2）年平均极涡强度的年际、年代际变化特征与极涡面积有相似之处，但不同年份存在显著差异；各分区的强度变化与北半球类似（特别是Ⅰ区）；夏季的年际变化幅度最大，春、夏季年代际变化的特征明显，秋季最弱。（3）北极涡中心位置通常并不在北极点，各分区极涡总面积所占的百分比有明显差异，且有月际变化，这些差异与海陆热力差异造成的环流的差异密切相关；极涡的主要位置有一定的年际、年代际变化特征；极涡中心位置主要偏向亚洲大陆及太平洋一侧。

英文摘要：

The area size and intensity of 300 hPa Arctic polar vortex and their seasonal changes are estimated from 1949 to 2002 based upon the 54-year NCEP/NCAR reanalysis monthly mean geopotential height data. By means of linear trend estimate, Morlet wavelet analysis and binomial coefficient smooth, the interannual and interdecadal variation characteristics of 300 hPa Arctic Polar vortex are studied, including the variation of area, intensity and location. The results show that. （1） Before middle age of 1970s, annual area size of Arctic polar vortex trend to rise, with small fluctuating, and after that, with clear undulating, it trend to decrease, but the size has a linear decline trend during 1949--2002. The linear variation trends of region Ⅰ and Ⅱ are much smaller than that of region Ⅳ. The interannual variation in summer is the most obvious, and the variation in autumn is the smallest. The area of seasonal Arctic polar vortex also trend to contract linearly, especially in winter. （2） Intensity of annual polar vortex has the similar characteristics of the interannual and interdecadal variations with area, but the linear trend is very slight. Each region resemble Northern Hemisphere about the variation of intensity, especially region Ⅰ , except for local difference in some period of time. The interannual variation in summer has the largest extent, and inter-decadal variation in spring and summer is much more prominent than in autumn. （3） The center of northern polar vortex is not at Arctic pole. The percentage of the polar vortex size in each quadrant has distinct difference, and it varies from January to December, which is close related to thermodynamic difference over sea-land. The main location of polar vortex has interannual and interdecadal variation characteristics. The percentage of the vortex size in quadrant Ⅰ and Ⅱ trend to ascend, while descend in quadrant Ⅲ and Ⅳ, and the linear trend coefficient is small for quadrant Ⅰ and Ⅲ. The center of polar vortex mainly displace toward