The Agulhas system is the strongest western boundary current system in the Southern Hemisphere and plays an important role in modulating the Indian-to-Atlantic Ocean water exchange by the Agulhas leakage.It is difficu...The Agulhas system is the strongest western boundary current system in the Southern Hemisphere and plays an important role in modulating the Indian-to-Atlantic Ocean water exchange by the Agulhas leakage.It is difficult to measure in situ transport of the Agulhas leakage as well as the Agulhas retroflection position due to their intermittent nature.In this study,an innovative kinematic algorithm was designed and applied to the gridded altimeter observational data,to ascertain the longitudinal position of Agulhas retroflection,the stability of Agulhas jet stream,as well as its strength.The results show that the east-west shift of retroflection is related neither to the strength of Agulhas current nor to its stability.Further analysis uncovers the connection between the westward extension of Agulhas jet stream and an anomalous cyclonic circulation at its northern side,which is likely attributed to the local wind stress curl anomaly.To confirm the effect of local wind forcing on the east-west shift of retroflection,numerical sensitivity experiments were conducted.The results show that the local wind stress can induce a similar longitudinal shift of the retroflection as altimetry observations.Further statistical and case study indicates that whether an Agulhas ring can continuously migrate westward to the Atlantic Ocean or re-merge into the main flow depends on the retroflection position.Therefore,the westward retroflection may contribute to a stronger Agulhas leakage than the eastward retroflection.展开更多
基于卫星高度计数据、模式数据和同化资料揭示了东印度沿岸流(East India Coastal Current, EICC)年周期上的时空分布特征,并探讨了其可能的影响机制及热盐输运。在年周期上EICC呈现3种分布状态,受季风影响,在东北季风前期(10—12月)和...基于卫星高度计数据、模式数据和同化资料揭示了东印度沿岸流(East India Coastal Current, EICC)年周期上的时空分布特征,并探讨了其可能的影响机制及热盐输运。在年周期上EICC呈现3种分布状态,受季风影响,在东北季风前期(10—12月)和后期(2—5月)为一致的南向(北向)流动;而6—8月EICC呈3段式分布,与另外两个时间段明显不同,表现为9°N以南、16°N以北区域的南向流动和9°—16°N区域的北向流动。前人研究认为印度东海岸的局地风应力是EICC的主要机制,本研究发现除局地风应力外,来自孟加拉湾中部的艾克曼抽吸(EkmanPumping)在全年也发挥着重要作用,并在2—5月(10—12月)驱动EICC的北向(南向)流动,而局地风应力则在10—12月有利于EICC的南向流动。EICC是孟加拉湾低盐水向赤道东印度洋和阿拉伯海输运的一个因素,在海盆间的热盐交换上发挥着重要作用。EICC的热输运在6—12月(2—5月)有利于(不利于)湾内温度的升高;盐输运则在全年都有利于孟加拉湾内盐度的增加。此外,EICC的一致南向(北向)流动以及3段式结构促进了湾内热盐的再分配,对于维持北印度洋的热量和盐度收支平衡具有重要作用。展开更多
基金The National Key R&D Program of China under contract No.2019YFA0606702the National Natural Science Foundation of China under contract Nos 42176222,91858202,41630963,and 41776003+1 种基金the National Science Foundation under contract No.NSF-IIS-2123264the fund suported by the National Aeronautics and Space Administration under contract No.NASA-80NSSC20M0220.
文摘The Agulhas system is the strongest western boundary current system in the Southern Hemisphere and plays an important role in modulating the Indian-to-Atlantic Ocean water exchange by the Agulhas leakage.It is difficult to measure in situ transport of the Agulhas leakage as well as the Agulhas retroflection position due to their intermittent nature.In this study,an innovative kinematic algorithm was designed and applied to the gridded altimeter observational data,to ascertain the longitudinal position of Agulhas retroflection,the stability of Agulhas jet stream,as well as its strength.The results show that the east-west shift of retroflection is related neither to the strength of Agulhas current nor to its stability.Further analysis uncovers the connection between the westward extension of Agulhas jet stream and an anomalous cyclonic circulation at its northern side,which is likely attributed to the local wind stress curl anomaly.To confirm the effect of local wind forcing on the east-west shift of retroflection,numerical sensitivity experiments were conducted.The results show that the local wind stress can induce a similar longitudinal shift of the retroflection as altimetry observations.Further statistical and case study indicates that whether an Agulhas ring can continuously migrate westward to the Atlantic Ocean or re-merge into the main flow depends on the retroflection position.Therefore,the westward retroflection may contribute to a stronger Agulhas leakage than the eastward retroflection.
文摘基于卫星高度计数据、模式数据和同化资料揭示了东印度沿岸流(East India Coastal Current, EICC)年周期上的时空分布特征,并探讨了其可能的影响机制及热盐输运。在年周期上EICC呈现3种分布状态,受季风影响,在东北季风前期(10—12月)和后期(2—5月)为一致的南向(北向)流动;而6—8月EICC呈3段式分布,与另外两个时间段明显不同,表现为9°N以南、16°N以北区域的南向流动和9°—16°N区域的北向流动。前人研究认为印度东海岸的局地风应力是EICC的主要机制,本研究发现除局地风应力外,来自孟加拉湾中部的艾克曼抽吸(EkmanPumping)在全年也发挥着重要作用,并在2—5月(10—12月)驱动EICC的北向(南向)流动,而局地风应力则在10—12月有利于EICC的南向流动。EICC是孟加拉湾低盐水向赤道东印度洋和阿拉伯海输运的一个因素,在海盆间的热盐交换上发挥着重要作用。EICC的热输运在6—12月(2—5月)有利于(不利于)湾内温度的升高;盐输运则在全年都有利于孟加拉湾内盐度的增加。此外,EICC的一致南向(北向)流动以及3段式结构促进了湾内热盐的再分配,对于维持北印度洋的热量和盐度收支平衡具有重要作用。
