与2003年梅雨期西太副高东西向运动有关的热带上空东风带扰动的结构和演变特征

利用NCEP/NCAR 1 000～10 hPa 2.5 (×2.5 (的再分析资料,分析了与西太平洋副热带高压(简称西太副高)东西进退相关系的热带对流层上空东风带扰动(简称EV)的结构和演变特征.结果表明:西太副高与其南侧的东风带扰动存在同时西进的过程,当西太副高南、北两侧的东、西风带上的扰动在相向运动中抵达同一经度上时,西太副高出现异常东退.热带对流层上空东风带扰动为中高层天气系统,它从对流层中层伸展到50 hPa高度附近,在200 hPa上表现得最为明显,在热力场上表现出"上暖强下冷弱"的垂直分布特征;在西太副高东退时,东风带扰动东西侧的辐散效应和垂直运动的性质发生了显著变化,东风带扰动中心附近的垂直速度场出现从上升运动到向下下沉运动转化的过程.

STRUCTURAL AND EVOLUTION CHARACTERISTICS OF THE EASTERLIES VORTEX OVER THE TROPICAL REGION RELATING TO THE EAST-WEST SHIFT OF THE SUBTROPICAL ANTICYCLONE OVER THE WESTERN PACIFIC OCEAN IN THE MEIYU PERIOD 2003

The different effects of anomalous convective activities in the tropical western Pacific on two persistent heavy rain events in South China in 2005 and 2006 are compared in this study.The data used consist of NOAA Outgoing Longwave Radiation(OLR) data,the NCEP-NCAR reanalysis and precipitation from meteorological stations in South China.Results show that the persistent heavy rain in 2005 was related to the 10-25-day westward propagation of convective activities in the tropical western Pacific from about 150 °E.The physical mechanism is interpreted as a Gill-type response of subtropical anticyclone westward extension during weak convective activities period over the Philippine Sea.Our researches also show that the persistent heavy rain in 2006 had longer period than that in 2005,and the subtropical anticyclone persists westward in the earlier summer which is possibly related to the lasting anomalous strong convective motion in the southern branch of Intertropical Convergence Zone(ITCZ) in the tropic western Pacific.The anomalous convective activities affect the local Hadley circulation over the western Pacific with anomalous ascending motion south of the equator and anomalous descend motion north of it,in favor of the westward extension of the subtropical anticyclone for a long time.Comparison between the two persistent heavy rain events indicates different physical effects of convective activities in the tropical western Pacific,though both effects are helpful to the subtropical anticyclone westward extension as a common character of large-scale circulation backgrounds for persistent heavy rain events in South China.