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Weiwei Zhang, Xiaoyi Yang, Wei Zhuang, Xiaohai Yan. On the longitudinal shifts of the Agulhas retroflection point[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2295-x
Citation: Weiwei Zhang, Xiaoyi Yang, Wei Zhuang, Xiaohai Yan. On the longitudinal shifts of the Agulhas retroflection point[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2295-x

On the longitudinal shifts of the Agulhas retroflection point

doi: 10.1007/s13131-023-2295-x
Funds:  The National Key R&D Program of China under contract No. 2019YFA0606702; the National Natural Science Foundation of China under contract Nos 42176222, 91858202, 41630963, and 41776003; the National Science Foundation under contract No. NSF-IIS-2123264; the fund suported by the National Aeronautics and Space Administration under contract No. NASA-80NSSC20M0220.
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  • Corresponding author: E-mail: xyyang@xmu.edu.cn
  • Received Date: 2023-11-20
  • Accepted Date: 2024-01-24
  • Available Online: 2024-03-15
  • 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.
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