The physical processes involved in the formation of the ENSO cycle, as well as the possible roles of the Hadley circulation(HC), Walker circulation(WC), and the propagating waves of the Southern Oscillation/Northern Oscillation(SO/NO) in its formation, were studied using composite and regression methods. The analysis showed that the convection and heat release triggered by ENSO in the central-eastern equatorial Pacific are the primary drivers for the 3–5 year cycle of the HC, WC and the meridional/zonal circulation. The HC plays a key role in the influence of ENSO on the circulation outside the tropics through angular momentum transportation. Meanwhile, the feedback effects of the anomalous circulation in the mid-high latitudes on ENSO are accomplished by the propagating waves of SO/NO associated with the evolutions of HC and WC.These propagating waves are the main agents of the connections among the meridional/zonal circulation outside the tropics,the Asian/Australian monsoon, the anomalous easterly/westerly winds over the tropical Pacific, and ENSO events. It was found that the 3–5 year cycle of the meridional/zonal circulation forced by ENSO is quite different from the several-week variation of the circulation index triggered by the inner dynamic processes of the atmosphere. The former occurs at the global scale with a definite flow pattern, while the latter occurs only in a wide area without a definite flow pattern. Finally, a physical model for the formation of the ENSO cycle composed of two fundamental processes at the basin and global scale,respectively, is proposed.
Based on the ERA reanalysis winds data, the multi-time scale variations of Somali jet are analyzed synthetically. The jet's influences on rainfall in China on interannual, interdecadal and sub-monthly scales are also studied using correlation and composite analyses. The results demonstrate that the interdecadal variations of the jet are significant.The Somali jet became weaker in the 1960 s and became the weakest in the early 1970 s before enhancing slowly in the late 1970 s. Moreover, the relation between the Somali jet and summer precipitation in China is close, but varies on different timescales. Preliminary analysis shows that the intensity variations in May and June during the early days of establishment are well correlated with summer precipitation in China. The Somali jet intensity on the interdecadal scale is closely related with interdecadal variations of the precipitation in China. Regardless of leading or contemporaneous correlation, the correlations between the Somali jet intensity and the rainfall in northern and southern China show obvious interdecadal variations. Moreover, the link between the anomalies of the jet intensity in May-August and precipitation evolution on synoptic scale in China is further studied. China has more rainfall with positive anomalies of the Somali jet but less rainfall with negative anomalies during the active period of the jet. The influence of positive Somali jet anomalies on China precipitation is more evident.
地球系统由固体地球、大气和海洋等流体层组成。在自转的地球上相对于地球表面运动的空气,因受到摩擦和山脉的作用,与转动地球之间产生转动力矩,即为大气角动量(Atmospheric angular momentum,AAM)。早期有关AAM的研究主要用于解释大气环流中信风和盛行西风得以维持的原因,而近些年来研究者更注重研究AAM的变化问题,包括山脉和摩擦力矩、角动量及其输送的季节、年际和年代际等多时间尺度的变化问题,并将其与日长(Long of day,LOD)变化、厄尔尼诺和南方涛动等地球、海洋和大气现象联系起来。作为一个描述大气环流的基本变量,AAM的平衡和异常反映了大气活动与固体地球、海洋在多时空尺度上的耦合过程。比如,大气的季节性质量重新分布(大气压)和运动(纬向风)的驱动(也就意味着AAM发生了变化)可导致LOD随之发生相应的季节性变化;从角动量守恒的角度来讲,当大气自西向东的角动量增加时,固体地球的角动量必然减小,地球自转速度减慢,LOD增大,反之亦然。因此,AAM的研究一直以来都受到气象学家、天文学家和地球科学家等的青睐。主要总结了20世纪80年代以来在地气系统角动量交换和平衡、AAM的变化及其与大气、海洋活动、地球自转的联系等方面的相关研究进展,并指出了当前研究中所存在的一些问题,为未来的科学研究提供参考。
