夏季东亚西风急流扰动异常与副热带高压关系研究

Relationships Between Perturbation Kinetic Energy Anomaly Along East Asian Westerly Jet and Subtropical High in Summer

利用1979—2003年NCEP/NCAR月平均再分析资料,探讨夏季(6—8月)200 hPa东亚西风急流扰动异常与南亚高压和西太平洋副热带高压的关系。研究指出:夏季200 hPa东亚西风急流扰动动能加强(减弱),东亚西风急流位置偏南(偏北)、强度偏强(偏弱);东亚西风急流扰动动能强弱不仅与北半球西风急流强弱和沿急流的定常扰动有关,而且还与东亚地区高、中、低纬南北向的扰动波列有关,亚洲地区是北半球中纬度环球带状波列异常最大的区域。夏季200 hPa东亚西风急流扰动动能加强(减弱),南亚高压的特征为位置偏东(偏西)、强度加强(减弱);西太平洋副热带高压的特征为位置偏南(偏北)。东亚环流特别是500 hPa西太平洋副热带高压对东亚西风带扰动异常的响应由高空东亚西风急流南侧的散度场及其对流层中下层热带和副热带地区的垂直速度距平场变化完成。

In summer, upper level subtropical westerly jet stream along 40°N over East Asia is one of the most important large-scale circulation systems which influence weather and climate change over east China. At the same time, it is also a wave-guide along Rossby wave activity. Thus, it is necessary to define an objective and quantitive perturbation kinetic energy （Ek） index along East Asian westerly jet （EAWJ）, and Ek annual variation and anomalies are investigated. Moreover, the relationships between Ek and EAWJ intensity and EAWJ position are examined, lastly the configuration and connection processes between Ek variability along EAWJ and South Asia high （SAH） and western pacific subtropical high （WPSH） in summer are confirmed by NCEP/NCAR reanalysis dataset from 1979 to 2003. u basic and v basic are defined by wave number k 〈 3 based on wind u and v in 200 hPa calculated by Fourier expressions, the perturbation kinetic energy of Rossby wave along EAWJ is defined by k≥3 wave activity,and Rossby wave perturbation （u′, v′） = （u , v） - （ub vb）,Ek= （u′· u′ ＋ v′· v′）/2 which is averaged in the area of latitude with maxima zonal wind shifted ±5° and in 100°-140°E,so normal Ek is defined as Rossby wave activity index along EAWJ which also includes meridional displacement variability of EAWJ. EAWJPⅠ（East Asian westerly jet position index） is defined by the difference of zonal wind in 200 hPa between 35°-40°N, 100°-140°E and 40°-45° N, 100°-140°E, and EAWJⅡ（East Asian westerly jet intensity index） is defined by the summation of zonal wind in 200 hPa averaged by 35°-45°N, 100°-140°E. The resuits show that EAWJ is southward （northward） than the normal and its intensity becomes stronger （weaker） while Ek strengthened （weakened）. Not only Ek variations are associated with EAWJ intensity and steady Rossby wave perturbation along westerly jet in summer, but also south--north wave train anomaly in East Asia. Height anomaly in Asia mid-latitude area is most remarkable. When Ek appears stronger （weaker） than normal, center position of circumglobal wave train wave in mid-latitude zone moves to southern （northern）. The correlation coefficient is 0.56 between E k and SAM intensity,0.66 between Ek and SAM eastward ridge point position, and -0.52 between Ek and WPSH ridge line position during 1979-2003 summer respectively, all are over 99% level. While Ek appears stronger（weaker）than normal, SAM moves to eastward （westward） and stronger （weaker） than the normal. At the same time, WPSH is southward （northward） than the normal. It is found that the response of WPSH to Ek anomaly is going with the change of divergence-convergence over East Asia in 200 hPa and vertical motion in tropic and subtropical zone from surface to upper air.