用自由模对1998年夏季阻塞形势的诊断分析

DIAGNOSE ANALYSE ATMOSPHERIC BLOCKING HIGH BY FREE MODE

中文关键词:  阻塞高压  自由模  诊断分析  环流异常

英文关键词:Blocking  Free mode  Diagnose and analyse  Circulation anomaly

中文摘要:

      签于大气自由模和阻塞高压的重要性,首先简要介绍阻塞高压与中国夏季降水的关系及1998年夏季500hPa异常环流场;然后利用21波菱形截断的谱方法求出无粘性、无强迫正压涡度方程的自由解,即和实际大气流场十分接近的大气自由模,并讨论其特征;最后利用大气自由模的特征诊断分析了实际大气的环流特征,并重点用其分析了1998年夏季的大气环流异常形势.结果表明大气自由模能很好地反映大气环流大尺度特征,而略去了中、小尺度涡旋;大气自由模的流场和绝对涡度场之间的散点图反映了(q,Ψ)的函数关系是分段线性或非线性的,尽管实际流场与绝对涡度场之间的点阵图反映两者之间成不同斜率的线性函数关系,但点阵比较发散,不能突出某些重要系统;1998年夏季实际大气自由模态突出了大气环流的重要特征,例如,越赤道气流、西风急流、副热带高压、阻塞高压及两极的边界效应等;通过自由模态的特征可以识别出纬向流及阻塞高压的持续异常,利用自由模的稳定性判断阻塞高压的稳定性,不稳定模态可以维持一段较长的时间,且由于这些不稳定的模存在,才使1998年6月中旬到下旬的中高纬阻塞高压稳定维持.

英文摘要:

      Aimed at stud of atmospheric free mode and blocking high,firstly,the relationships between blockings and China summer rainfall are clarified,and the 500 hPa height in the summer of 1998 are det ailed analysed.Then,using 21-wave rhomboidal truncation spectral model procedure,it is searched for steady solutions to the inviscid,unforced barotrpic vorticity equation,which are called free solutions or free modes.These free solutions are extremely similar to the planetary scale structure of observed flows.Thirdly,the characteristics of atmospheric free modes are particularly discussed.Finaly,by virtue of at mospheric free modes,we diagnose observed at mospheric circulation and put stress on analyzing the anomalous circulation during the summer of 1998,and the Normal-mode instability analysis is performed to examine observed stability of free modes and blocking.The results show the following:(1)The mid-high latitudes blocking has a close relationship with China summer rainfall,and the atmosphere underwent three times blocking anomaly in the summer of 1998.(2) Each observed flow is corresponding to a free mode,and the scatter field between observed free mode streamf unction and the corresponding absolute vorticity (also called plots) reflects their subsection-linear even nonlinear relationship.The plots for observed stream flow lay out the linear relationship in different slope between streamfunction and the corresponding absolute vorticity,but the scatters are relatively emanative.(3) Observed atmospheric free modes show most characteristics of at mospheric circulation in large scale,while neglect the mesoscale and microscale vortex.