极涡对北太平洋风暴轴影响及成因初探

Study on impact of polar vortex on north Pacific storm track and its possible mechanism

利用美国NCEP/NCAR再分析资料,初步探讨了1969—2013年冬季北半球极涡对北太平洋风暴轴的影响及可能的物理机制.结果表明:风暴轴主要分布在120°E—120°W、30°—60°N之间,扰动最强中心位于45°N附近.奇异值分解表明,极涡与风暴轴之间主要存在两种耦合空间变化特征.当极涡在极区增强(减弱)时,风暴轴在其气候平均位置增强(减弱);当极涡增强并向北太平洋地区移动时,相对于平均状态,风暴轴在45°N以南地区偏强;而当极涡向北美大陆移动增强时,相对于平均状态,45°N轴线以北地区风暴轴偏强.回归分析进一步表明了北半球极涡影响北太平洋风暴轴变化的原因,极涡通过改变500h Pa位势高度场的遥相关形态特征,进而改变东亚西风急流及风暴轴上游地区斜压性的位置与强度,从而导致风暴轴的强度发生变化.

Based on the NCEP / NCAR reanalysis data from 1969 to 2013,the impacts of the northern polar vortex on the North Pacific storm track and its possible physical mechanism in recent 45 winters were analyzed. The results showthat storm track is mainly located in the range of 120°E—120°W,30°—60°N,and the strongest disturbance center is near 45°N. Singular Value Decomposition（ SVD） suggests that there are two major coupled modes between the polar vortex and storm track. The first coupled mode depicts that the storm track is stronger（ weaker）in the vicinity of its long-term mean locations while the polar vortex is stronger（ weaker） in the polar region. The second mode depicts that as the polar vortex increases and shifts to the North Pacific,the storm track comparing to its mean state is stronger in the south of its long-term mean locations. On the contrary,as the polar vortex increases and moves to the north America,the storm track comparing to its mean state increases in the north of its long-term mean locations. A regression analysis further suggests that the anomalous change of polar vortex may give rise to change at 500 h Pa geopotential height,and then change the East Asia westerly jet and the baroclinicity in the upstream of the storm track,and finally the storm track itself.