Both the tropical Indian and tropical Pacific Oceans are active atmosphere-ocean interactive regions with robust interannual variability, which also constitutes a linkage between the two basins in the mode of variability. Using a global atmosphere- ocean coupled model, we conducted two experiments （CTRL and PC） to explore the contributions of Indian Ocean interannual sea surface temperature （SST） modes to the occurrence of E1 Nino events. The results show that interannual variability of the SST in the Indian Ocean induces a rapid growth of E1 Nino events during the boreal autumn in an E1 Nino developing year. However, it weakens E1 Nino events or even promotes cold phase conversions in an E1 Nino decaying year. Therefore, the en- tire period of the E1 Nino is shortened by the interannual variations of the Indian Ocean SST. Specifically, during the E1 Nino developing years, the positive Indian Ocean Dipole （IOD） events force an anomalous Walker circulation, which then enhances the existing westerly wind anomalies over the west Pacific. This will cause a warmer E1 Nino event, with some modulations by ocean advection and oceanic Rossby and Kelvin waves. However, with the onset of the South Asian monsoon, the Indian Ocean Basin （IOB） warming SST anomalies excite low level easterly wind anomalies over the west tropical Pacific during the El Nino decaying years. As a result, the E1 Nino event is prompted to change from a warm phase to a cold phase. At the same time, an associated atmospheric anticyclone anomaly appears and leads to a decreasing precipitation anomaly over the northwest Pacific. In summary, with remote forcing in the atmospheric circulation, the IOD mode usually affects the E1 Nino during the developing years, whereas the IOB mode affects the E1 Nino during the decaying years.
HONG XiaoYuanHU HaiBoYANG XiuQunZHANG YuanLIU GuoQiangLIU Wei
This paper attempts to analyze in detail the remote influence of the Indian Ocean Basin warming on the Northwest Pacific （NWP） during the year of decaying E1 Nifio. Observation data and the Fast Ocean- Atmosphere coupled Model 1.5 were used to investigate the triggering conditions under which the remote influence is formed between the positive sea surface temperature （SST） anomaly in the North Indian Ocean and the Anomalous Northwest Pacific anticyclone （ANWPA）. Our research show that it is only when there is a contributory background wind field over the Indian Ocean, i,e., when the Indian Summer Monsoon （ISM） reaches its peak, that the warmer SST anomaly in the North Indian Ocean incites significant easterly wind anomalies in the lower atmosphere of the Indo-West tropical Pacific. This then produces the remote influence on the ANWPA. Therefore, the SST anomaly in the North Indian Ocean might interfere with the prediction of the East Asia Summer Monsoon in the year of decaying E1 Nifio. Both the sustaining effect of local negative SST anomalies in the NWP, and the remote effect of positive SST anomalies in the North Indian Ocean on the ANWPA, should be considered in further research.
