1] CSIRO Marine and Atmospheric Research, Aspendale, Victoria, 3195 Australia [2] Physical Oceanography Laboratory, Qingdao Collaborative Innovation Center of Marine Science and Technology, Ocean University of China, Qingdao, 266003 China.
Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, The University of New South Wales, Sydney, 2052 Australia.
Nature. 2014 Jun 12;510(7504):254-8. doi: 10.1038/nature13327.
The Indian Ocean dipole is a prominent mode of coupled ocean-atmosphere variability, affecting the lives of millions of people in Indian Ocean rim countries. In its positive phase, sea surface temperatures are lower than normal off the Sumatra-Java coast, but higher in the western tropical Indian Ocean. During the extreme positive-IOD (pIOD) events of 1961, 1994 and 1997, the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents. This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west, leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries. Despite these serious consequences, the response of pIOD events to greenhouse warming is unknown. Here, using an ensemble of climate models forced by a scenario of high greenhouse gas emissions (Representative Concentration Pathway 8.5), we project that the frequency of extreme pIOD events will increase by almost a factor of three, from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century. We find that a mean state change--with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean--facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD.
印度洋偶极子是一种重要的海气耦合变率模态，影响着印度洋沿岸国家数以百万计人民的生活。在其正位相期间，苏门答腊-爪哇沿海的海面温度低于正常水平，但在西热带印度洋则较高。在 1961 年、1994 年和 1997 年极端正印度洋偶极子事件期间，东部冷却加强，并沿着赤道印度洋向西延伸，这是由于西风的平均风向和与之相关的向东流动的上层海洋流发生强烈逆转所致。这在赤道上的东印度洋至中印度洋造成异常干燥的条件，以及更远西部的大气辐合，导致东热带非洲国家发生灾难性洪水，但东印度洋沿岸国家则遭受严重干旱。尽管这些后果严重，但目前还不知道温室变暖对正印度洋偶极子事件的反应。在这里，我们使用一组由高温室气体排放情景（代表性浓度路径 8.5）驱动的气候模型进行模拟，预计极端正印度洋偶极子事件的频率将增加近两倍，从 20 世纪每 17.3 年发生一次增加到 21 世纪每 6.3 年发生一次。我们发现，一种平均状态的变化——赤道西风和向东的海洋流减弱，同时西赤道印度洋的变暖速度快于东赤道印度洋——有利于更频繁地发生风和海洋流的逆转。这导致更频繁的极端正印度洋偶极子事件，表明受正印度洋偶极子影响的地区极端气候和天气事件的频率正在增加。
