印度洋偶极子向海盆一致模转变的年代际变化及其成因
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国家自然科学基金资助项目(41975063)


Interdecadal variation of transition from Indian Ocean Dipole to Indian Ocean Basin Mode and its causes
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    摘要:

    利用3种百年时间尺度的海温资料,探讨了印度洋偶极子(India Ocean Dipole,IOD)向海盆一致模(Indian Ocean Basin,IOB)年际转变的年代际变化,结果发现1940—1970年几乎不存在这一转变现象,1970年以后该现象则十分显著。研究表明,IOD与ENSO之间海气耦合作用的年代际变化是这一转变现象的主要原因,1940—1970年IOD与ENSO之间发生发展相互独立,而1970年以后联系密切。通过进一步对物理量场的诊断分析,揭示了其中主要的动力机理:1970年以前,热带印度洋上空形成的季风环流异常无法与热带太平洋的沃克环流异常进行耦合,IOD事件发生时无法与热带太平洋产生联系。反之,1970年以后,热带两大洋上空两个纬圈环流异常之间耦合作用强烈,正(负) IOD事件发生时,通过海气相互作用,促进El Niño (La Niña)发展,印度洋又会受到来自ENSO的正反馈作用。因此这种“齿轮式”耦合模型能一直持续到冬季和次年春季,热带印度洋上空持续受到东(西)风异常的影响和低层环流的引导,西印度洋有次表层暖水的流入(出),加上印度洋本身海盆尺度较小,西边的暖(冷)水区显著增大,东西海温异常差异迅速减小并向海盆一致变暖(冷)转变,导致了后期冬季、春季正(负) IOB事件的出现。

    Abstract:

    Based on three centennial SST data,this paper investigated the interdecadal variation of the interannual transition from Indian Ocean Dipole (IOD) to Indian Ocean Basin Mode (IOB) by using statistical analysis and interannual signal removal methods.Results show that there is almost no such transition from 1940 to 1970,but it is very significant after 1970.It is found that the interdecadal variation of air-sea coupling between IOD and ENSO is the main reason for this transition.The occurrence and development of IOD and ENSO are independent from 1940 to 1970,but they are closely related after 1970.Through further diagnostic analysis of physical quantity fields,this paper reveals the main dynamic mechanism.Before 1970,the anomalous monsoon circulation over the tropical Indian Ocean could not be coupled with the anti-walker circulation over the tropical Pacific Ocean,and the IOD event cannot be connected with the tropical Pacific when it occurs.On the contrary,after 1970,the coupling effect between the two latitudinal circulation anomalies over the two tropical oceans is strong.When the positive (negative) IOD event occurs,it promotes the development of El Niño (La Niña) through air-sea interaction,and the Indian Ocean will receive the positive feedback from ENSO.Therefore,this “geared-like” coupling model can last until winter and the following spring,and the tropical Indian Ocean is continuously affected by the easterly (westerly) anomaly and guided by the low-level circulation.There is an inflow (outflow) of subsurface warm water in the western Indian Ocean,coupled with the small basin size of the Indian Ocean itself,so the western warm (cold) water area increases significantly,the difference between the east and west SST anomalies rapidly decreases,and it changes to the uniform warming (cold) of the basin,which leads to the occurrence of positive (negative) IOB events in the late winter and spring.

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郭品文,吴清传,2022.印度洋偶极子向海盆一致模转变的年代际变化及其成因[J].大气科学学报,45(4):562-572. GUO Pinwen, WU Qingchuan,2022. Interdecadal variation of transition from Indian Ocean Dipole to Indian Ocean Basin Mode and its causes[J]. Trans Atmos Sci,45(4):562-572. DOI:10.13878/j. cnki. dqkxxb.20200113009

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  • 收稿日期:2020-01-13
  • 最后修改日期:2020-03-17
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  • 在线发布日期: 2022-07-28
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