Two anomalous convective systems in the tropical western Pacific and their influences on the East Asian summer monsoon

根据经验正交函数(EOF)分解向外长波辐射资料,发现在热带西太平洋存在两个异常对流系统。除经典的菲律宾对流系统外(PC),在密克罗尼西亚群岛附近还存在另一个对流系统(MC)。MC是EOF分解的第一分量,解释的方差要大于PC。两个对流系统均受到热带海表温度异常的调制,其中PC与El Ni駉有关,而MC则与夏季中东太平洋海表温度异常有关。两个对流系统都能对东亚夏季风产生影响。一般而言,对流增强(减弱)时,西太平洋副高东退(西伸),强度减弱(增强)。PC减弱(增强)时,长江流域到日本的夏季风降水增加(减少)。与PC相比,MC对东亚大陆降水的影响较弱。此外,对流减弱的影响要大于对流增强的影响。

By decomposing outgoing Iongwave radiation through empirical orthogonal function （EOF） analysis, the authors identify two anomalous convective systems in the tropical western Pacific. Besides the classical convective system near the Philippines （PC）, there is another convective system near the Federated States of Micronesia （MC）. As the first EOF component in this region, the variance explained by MC is higher than that by PC. Both MC and PC are regulated by the tropical sea surface temperature （SST） anomalies. While PC is associated with an El Ni^o event, MC is correlated with SST anomalies in the central and eastern Pacific during summer. It is also found that the East Asian summer monsoon （EASM） is influenced by these two convective systems. In general, enhanced （suppressed） convection corresponds to an eastwards （westwards） western Pacific subtropical high with weak （strong） intensity. Besides, the summer monsoon rainfall from the Yangtze River basin to Japan tends to increase （decrease） when PC is suppressed （enhanced）. By comparison, the influence of MC is generally weak, with vague signals in the East Asian continent. Moreover, the influence of suppressed convection on the EASM is more significant than that of enhanced convection.