水汽在热带大气低频振荡传播中的作用分析

Role of Moisture in Causing Eastw ard Propagation of the Madden-Julian Oscillation

使用一对由近赤道地区平均的850 h Pa纬向风场（U850）、200 h Pa纬向风场（U200）和卫星观测的向外长波辐射（OLR）数据组成的综合场的经验正交函数（EOF1,EOF2）来定义Madden-Julian oscillation（MJO）,将每日观测的数据投影到这一对经验正交函数上得到一对时间系数,称为一对实时多变量的MJO指数（RMM1,RMM2）。用这一对MJO指数来表示MJO的强度和相位,得到历史上强MJO活动的时间,选取最近2011年9—11月的一次较强MJO活动进行分析,画出这次MJO活动的二维相位空间,确定每个阶段MJO的活动中心。通过OLR异常场的分析确定了在整个MJO活动中对流中心提前MJO活动中心1~2个相位的相关关系。分析OLR异常场和对流层低层（850 h Pa）风场的空间结构,在对流中心刚形成时,由于低层辐合高层辐散,对流层低层对流中心的东侧为东风异常,西侧为西风异常。异常风场向东的移速比对流中心的移速快,在之后的阶段,风场的辐合中心位于对流中心的偏东侧,而对流层高层的分析表明风场辐散中心也位于对流的偏东侧,这种高低空配置使得水汽的辐合中心也将位于偏东侧。整层大气可降水场的空间结构表明,可降水的正异常中心位于对流中心偏东侧,与水汽的辐合中心预计一致。在对流中心东西侧水汽分布的不均匀造成了对流中心的向东传播,也解释了MJO活动中心的向东传播。

Madden-Julian Oscillation （MJO） was defined by a pair of empirical orthogonal functions （EOFS） of the combined fields of near-equatorially averaged 850 hPa zonal wind,200 hPa zonal wind, and satellite-observed outgoing longwave radiation （OLR）data. Projection of the daily observed data onto the multi- ple-variable EOFS yields principal component （PC） time series, which were called the Real-rime Multivariate MJO series 1 （RMM1） and 2 （RMM2）.The two series could characterize daily amplitude and phase, historical daily time series were displayed. A most recent strong MJO activity was main researched object in this paper. It was convenient to diag- nose the state of the MJO as a point in the two-dimensional phase space defined by RMM1 and RMM2,points represent the location of the MJO. Analysis of anomaly field of OLR suggested that one or two phase MJO center lag behind en- hanced convection. The spatial pattern of composite OLR and wind vector anoma- lies showed that the convergence of wind anomalies in the lower troposphere locate at the east of enhanced convection and the divergence of wind anomalies in the upper troposphere also locate at the east of enhanced convection. Besides, the enhanced entire atmosphere precipitable water anomalies existed in same place, which consistant with center of the convergence of wind anomalies. The contribution of moisture asymmetry was positive over the eastward propagation of the center of convection, and also over the eastward propagation of the MJO.