印度夏季风爆发时间的年代际变异对春季型IOD的影响

The unseasonable Indian Ocean Dipole (IOD) is a new type of IOD that can only be observed after mid-1970s. The frequency of unseasonable IOD has increased significantly during the past decades, and this tendency has already induced great impacts on the climate in the Indian Ocean and adjacent regions. However, the mechanism for decadal variability of the unseasonable IOD is not clear. Most unseasonable IODs are triggered by early onset of the Indian summer monsoon. Preliminary results suggest that the variation of monsoon onset date also plays a dominant role in the decadal variability of unseasonable IOD. This project will investigate the influence of decadal variability of Indian summer monsoon onset date on the unseasonable IOD by data analysis and model experiments.The decadal variability of monsoon onset date and the corresponding atmospheric anomaly will be studied. Physical processes that are most important to the connections between these monsoon variations and the unseasonable IOD will be further examined. The mean state change in oceanic and atmospheric conditions of boreal spring and summer will also be studied, with focus on the major factors contributing to the variations of unseasonable IOD. We then will evaluate the relative importance of the monsoon variability and the mean state change for the decadal variability of the unseasonable IOD. How the unseasonable IOD will change under future climate warming and its corresponding climate implications will also be discussed.

春季型印度洋偶极子（Indian Ocean Dipole，简称IOD）是上世纪七十年代后出现的一种新型IOD。近四十年来，春季型IOD的发生频率呈现出显著的上升趋势，对印度洋及邻近地区的气候产生了重要影响。但是春季型IOD年代际变化的机制目前却并不清楚。印度夏季风提前爆发是春季型IOD的主要触发因子，多种迹象表明，在年代际尺度上该因子也是导致春季型IOD变化的重要原因。本项目将通过数据分析和数值实验，研究季风爆发时间变异影响春季型IOD年代际变化的途径和机制，探讨全球变暖条件下印度洋背景场的变异对季风与春季型IOD关系的调制作用，明确季风变异和背景场变异对春季型IOD年代际变化的相对贡献，揭示春季型IOD的年代际变化机制并预估其未来发展趋势和气候影响。该研究将丰富和完善关于春季型IOD的科学认识，有利于提高印度洋周边区域气候预测的准确性，为应对气候变化和防灾减灾提供科学依据。

本项目利用观测资料和再分析数据并结合模式结果，研究了印度洋夏季风爆发时间的年代际变异及其影响春季型印度洋偶极子（Indian Ocean Dipole，简称IOD）的物理机制；分析了全球变暖条件下印度洋背景场的变化趋势，以及这些变化对春季型IOD的影响。研究发现，过去四十年中，印度洋夏季风的爆发时间呈现逐渐提前的趋势。由于季风提前爆发能够导致赤道东风异常并触发春季型IOD，因此，季风爆发时间的提前是近几十年来春季型IOD增加的主要原因。同时，印度洋背景场也发生了显著的变化，受此影响，在春季型IOD形成和发展的重要季节，各种主要的海洋和大气反馈过程均表现出了加强的趋势。这些变化为春季型IOD的发展提供了有利条件，使季风异常导致的初始扰动更容易发展和加强。我们还应用模式结果预估了春季型IOD未来的变化趋势，结果表明，在全球持续增暖的情况下，春季型IOD的频率还将呈现继续增加的趋势。这将增加印度洋周边区域春季和夏季的气候变率和极端气候事件的发生频次。本项目的研究成果丰富和完善了关于IOD这一重要的海气相互作用事件的科学理论，将有助于提高对印度洋及邻近区域气候预测的准确性，同时为应对气候变化和防灾减灾提供了重要科学依据。