北太平洋阻塞的年际年代际变化及其与SST、遥相关及风暴路径的关系

利用NCEP／NCAR再分析资料，对1948／1949－1999／2000共52个冬季的北太平洋上空中纬度阻塞异常的气修特征进行了统计分析，小波分析和功率谱分析结果表明该区域阻塞发生的频数具有很明显的3－7年的年际振荡和年代际变化特征。同时2－7年带通平均的小波方差谱分析结果表明阻塞的这种年际变化的振幅存在着缓慢下降的趋势，且气候突变在20世纪70年代，这进一步证明了北太平洋上空的阻塞活动具有年代际变化特征。对强阻塞异常的冬季和弱阻塞异常的冬季分别进行合成分析，结果表明，对于阻塞异常强的冬季，北太平洋西向东北方向加强并分裂成两个中心，而SST异常在中纬度太平洋则对应着典型的PDO型，在赤道地区则为类La Nina型的海温分布。而对于阻塞异常弱的冬季则对应截然不同甚至相反的分布特征，即500hPa高度异常场表现为符号相反的PNA型，风暴路径中心在日界线附近呈纬向型分布。同时SST异常在赤道地区则为典型的El Nino型的海温分布。以上结果揭示出北太平洋阻塞活动的年际变化可能主要与热带海温的遥响应相联系，而年代际变化则主要与中纬度局地的PDO型海温及其通过斜压瞬变波的海－气相互作用有关。

Interannual and decadal variability of the north pacific blocking and its relationship to SST,teleconnection and storm tracks

Climatological features of mid-latitude blocking occurring over the North Pacific Ocean during 52winters (December to February) of 1948/1949-1999/2000 are statistically analyzed based onNCEP/NCAR reanalysis data. Significant interannual variation with a period of about 3-7 years as wellas decadal variability is found by wavelet analysis and power spectrum analysis. A decreasing trend of the2-7 year bandscale-averaged variance occurs throughout the 52 years and an abrupt shift from a higherstate to a lower state during the 1970s is also found, which suggests an interdecadal variation of the NorthPacific blocking. The possible relationship between the variability of blocking and sea surface temperature(SST), storm tracks and teleconnection are shown using composite analysis. In strong blocking anomalywinter (SBW), the geopotential height anomaly at 500 hPa exhibits a typical PNA (Pacific-NorthAmerican)-like wave-train pattern in the North Pacific. The storm tracks, representing the activity of tran-sient eddies, extend northeastward to the western coast of North America along the mid latitudes of about40°-50°N, with the SST anomaly exhibiting a Pacific decadal oscillation (PDO) mode at mid-latitude and aLa Nina-like pattern along the equator. Contrasting features appear in weak blocking anomaly winter(WBW).