Interannual Eddy Kinetic Energy Modulations in the Agulhas Return Current

• Published in: Journal of geophysical research. Oceans 2018-09, Vol.123 (9), p.6449-6462
• Main Authors: Zhu, Yanan, Qiu, Bo, Lin, Xiaopei, Wang, Fan
• Format: Article
• Language: English
• Subjects: Agulhas Current; Agulhas Return Current; Altimeters; Annual variations; Anomalies; Barotropic instability; Barotropic mode; Climate; Curl (vectors); Eddy currents; Eddy kinetic energy; Energy; Estimation; Flow stability; Geophysics; Height; Height anomalies; Inflow; Instability; Interannual variability; Kinetic energy; Ocean circulation; Ocean currents; Oceans; Satellite altimetry; Satellite observation; Satellites; Sea surface; Stress propagation; Temperature (air-sea); Upstream; Variability; Volume transport; Wind; Wind stress; Wind stress curl
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2018JC014333

Interannual variability in the mesoscale eddy field in the Agulhas Return Current (ARC) of 32–42°S and 15–35°E is investigated based on satellite altimeter observations and state estimate from the Estimating the Circulation and Climate of the Ocean, Phase II from 1993 to 2016. It is found that the interannual modulation of eddy kinetic energy in the ARC region is externally mediated by the wind stress forcing that generates the westward propagating sea surface height anomalies across the South Indian Ocean subtropical gyre. The wind‐forced sea surface height anomalies influence the upstream Agulhas Current volume transports. By modulating the intensity of barotropic instability of the ARC mean flow centered around the retroflection region, the Agulhas Current inflow variability leads to the downstream interannual eddy kinetic energy fluctuations in the ARC region. Key Points Interannual modulation of EKE in the ARC region is mediated by westward propagating SSH anomalies generated by basin‐wide wind stress forcing Upstream Agulhas Current inflow variability regulates the downstream interannual EKE fluctuations in the ARC region Barotropic instability is the main energy source controlling the regional EKE variability Plain Language Summary The interannual eddy kinetic energy modulations in the Agulhas Return Current region are investigated in this study on the basis of the satellite altimeter observations and the Estimating the Circulation and Climate of the Ocean, Phase II state estimate for the period of 1993–2016. The interannual eddy kinetic energy modulations in the Agulhas Return Current region are affected by the upstream Agulhas Current volume transports mainly via the barotropic instability. The wind stress curl forcing in the subtropical Indian Ocean is regarded as the major factor to modulate the Agulhas Current volume transport.