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The Observed Agulhas Retroflection Behaviors During 1993–2018.

Authors :
Zhu, Yanan
Li, Yuanlong
Zhang, Zhengguang
Qiu, Bo
Wang, Fan
Source :
Journal of Geophysical Research. Oceans; Dec2021, Vol. 126 Issue 12, p1-16, 16p
Publication Year :
2021

Abstract

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. Plain Language Summary: The Agulhas Retroflection (AR) is a key feature of the Agulhas Current system, and the choke point for the inter‐basin exchange between the Indian and Atlantic Oceans. The AR also serves as the origin of the Agulhas leakage that is constituted by northwestward moving eddies and rings radiated from the AR. Although there has been literature exploring the dynamics of the Agulhas Current and Agulhas leakage, our understanding of the AR variability is still incomplete. Using 26 years of updated satellite observation data of 1993–2018, we show that the mean longitude of the surface AR point is 17.5°E, and its fluctuation can be as wide as 7°−27°E. Owing to its strong variability and irregular behaviors, the AR does not possess a robust seasonal cycle. The AR behaviors are asymmetric: its residence time in the west tends to be much shorter than in the east. The interaction between the mean flow and mesoscale eddies is likely an essential regime controlling the AR variability. We also show that the AR variability can cause strong anomalies in regional sea surface temperature and air‐sea heat fluxes, which has potential influence on the local climate. Key Points: The mean longitude of the AR is 17.5°E with a standard deviation of 2.6°E and shows temporal asymmetry in westward and eastward phasesThe energy transfer from mean flow to eddies is likely the primary mechanism regulating the AR variabilityThe AR variability causes local SST anomalies of ∼0.5°C and surface heat flux anomalies of ∼10 W m−2 [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
21699275
Volume :
126
Issue :
12
Database :
Complementary Index
Journal :
Journal of Geophysical Research. Oceans
Publication Type :
Academic Journal
Accession number :
154346760
Full Text :
https://doi.org/10.1029/2021JC017995