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The Observed Agulhas Retroflection Behaviors During 1993–2018
March 03,2022

Yanan Zhu, Yuanlong Li, Zhengguang Zhang, Bo Qiu, Fan Wang

Published in Journal of Geophysical Research: Oceans, DEC 2021

Near the southern tip of the African continent, the Agulhas Current retroflects eastward to feed the Agulhas Return Current, giving rise to the Agulhas Retroflection (AR). The AR is dynamically unstable and radiates eddies and rings that constitute a portion of the Agulhas leakage. In this study, by analyzing 26 years (1993–2018) of updated satellite altimetry data, the spatial and temporal characteristic of the surface AR point are revisited. By adopting a refined identification algorithm of the AR point, we show that the AR longitude (XAR) fluctuates widely between 7° and 27°E on timescales ranging from days to months, without a stable seasonal cycle. The XAR variability also shows evident temporal asymmetry with shorter residence time at western positions. The retreat of the AR from the western to eastern positions tends to be swift, with 46% of the events completed in one day. In comparison, the intrusion from the eastern to western positions is much slower, with 32% of the events taking more than one month. The energy transfer from the mean flow to mesoscale eddies is likely the primary regime underlying the AR variability. Further analysis suggests that the AR variability causes sea surface temperature anomalies of ∼0.5°C through anomalous advection and thereby gives rise to turbulent heat flux anomalies of ∼10 W m−2, exerting potential impacts on the local climate.

Fig. (a) Time series of the daily XAR, with the West and East phases highlighted with green and red dots. (b) The probability density function of the daily AR longitude XAR. The blue line denotes the mean longitudinal position of AR, and the gray line is the standard deviation. The 20% westernmost (green) and 20% easternmost (red) positions are defined as the West and East phases of XAR oscillation, respectively. The snapshots of ADT for the (c) westernmost and (d) easternmost positions of AR (red dots), with the black lines denoting 0.73 and 0.7 m ADT contours in (c and d), respectively.

Zhu, Y., Li, Y., Zhang, Z., Qiu, B., & Wang, F. (2021). The observed Agulhas Retroflection behaviors during 1993–2018. Journal of Geophysical Research: Oceans, 126, e2021JC017995. https://doi.org/10.1029/2021JC017995

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