夏季MJO持续异常的主要特征分析

Analysis of the Major Characteristics of Persistent MJO Anomalies in the Summer

在MJO传播过程中,其活动中心并不总是规律地沿赤道东传。本文通过资料分析发现,夏季MJO的活动中心会出现东传停滞的情况,表现为MJO在赤道太平洋持续异常活跃或者在印度洋持续异常活跃两种形式。为更好描述MJO这种东传不明显的异常特征,本文定义了一个描述MJO持续异常的指数,并据此对夏季MJO持续异常的主要特征进行分析。通过小波分析的方法,发现夏季MJO持续异常时其振荡周期会出现缩短或变弱。通过对MJO持续异常状况下的大气环流进行合成对比分析后发现,夏季MJO的持续异常会对热带大气环流造成显著的影响。具体表现为:MJO夏季在赤道太平洋(印度洋)持续活跃的时候,赤道沃克环流减弱(增强),西太平洋哈得来环流增强(减弱),西太平洋副高位置偏北(偏南),赤道太平洋(印度洋)高层辐散且对流活跃。

During the eastward propagation of the MJO, its action centers are not always regularly distributed along the equator. Observational data analysis in the present study reveals that stagnant centers of the MJO action exist during the summer when the eastward propagation of the MJO becomes weak. The stagnant centers of the MJO action are present as two persistent and anomalously active centers in the equatorial Pacific and the equatorial Indian Ocean, respectively. To better investigate the anomalous characteristics associated with the inconspicuous eastward propagation of the MJO, an index is defined in this study to describe the persistent anomaly of the MJO with a focus on analysis of major characteristics of the persistent MJO anomaly. Based on results of Morlet wave analysis, it is found that the oscillation period becomes short when the persistent anomaly of the MJO occurs in the summer. A synthetic and comparative study of the atmospheric circulation under the persistent anomaly of summer MJO condition suggests that the persistent anomaly of the MJO can significantly affect tropical atmospheric circulation. Specifically, the Walker circulation in the equatorial region weakens （intensifies） in response to anomalies of summertime MJO activities in the equatorial Pacific （Indian Ocean）, while the Hadley Circulation intensifies （weakens） in the westem Pacific. Meanwhile, the West Pacific subtropical high shifts northward （southward）, while convection is active in the equatorial Pacific （Indian Ocean）, corresponding to upper-level divergence.