季风转换期印度洋经向热输运的年际变异及其机理

Interannual variability of meridional heat transport and its mechanism in the Indian Ocean during monsoon transitions

本文采用SODA3.4.2再分析数据和POP2海洋模式研究了季风转换期间(春季和秋季)热带印度洋经向热输运异常(Meridional Heat Transport Anomaly,MHTA)的年际变异特征。春季MHTA存在两个主要模态,即一致模态和辐合辐散模态:一致模态表现为热带印度洋上层一致的向北输运,受热带印度洋海温一致模相关的赤道反对称风场(赤道以北/南为东北风/西北风异常)调控;辐合辐散模态则呈现关于赤道对称的表层辐散次表层辐合特征,受控于赤道以南的热带西南印度洋和副热带东南印度洋海温偶极子。然而,秋季MHTA仅表现为辐合辐散模态,受到印度洋偶极子期间赤道东风和赤道外反气旋式风应力异常影响。此外,POP2敏感性试验也验证了印度洋海温模态影响下异常风场对MHTA的调控作用,即反对称的风引起一致向北的MHTA,赤道东风异常引起MHTA表层辐散、次表层辐合现象。因此,热带印度洋海气耦合模态年际变化对印度洋上层热量再分配有着重要的意义。

Interannual variability of meridional heat transport anomaly(MHTA)in the tropical Indian Ocean(IO)during monsoon transitions(boreal spring and autumn)is investigated based on SODA3.4.2 and POP2 results.There exist two leading interannual modes in spring,namely the consistent mode and the divergence and convergence(div/conv)mode.The consistent mode characterized by the northward MHTA in the upper IO,is controlled by the antisymmetric wind structures with northeasterlies anomalous northeasterlies(northwesterlies)to north(south)of the equator.However,the spring div/conv mode is featured by the meridional divergence in the surface layer and convergence in the subsurface layer on both side of the equator.Such a mode is modulated by the sea surface temperature anomaly(SSTA)dipole in the tropical southwestern IO and subtropical southeastern IO south of the equator.In autumn,the div/conv mode is dominated by the IOD-induced equatorial easterlies and associated anticyclonic wind stress anomalies in the off-equatorial regions.The POP2 model sensitivity experiments confirm the roles of anomalous winds induced by the Indian Ocean SSTA modes in modulating the MHTA,that is,the antisymmetric winds induce northward MHTA,while the anomalous easterly winds lead to the div/conv pattern.Therefore,the interannual variability of air-sea coupled modes in the IO plays a vital role in the basin-scale and hemisphericscale heat exchanges.