Interannual to Multidecadal Forcing of Mesoscale Eddy Kinetic Energy in the Subtropical Southern Indian Ocean. Issue 11 (13th November 2018)

• Record Type: Journal Article
• Authors: Delman, Andrew S.; Lee, Tong; Qiu, Bo
• Is Part Of: Journal of geophysical research. Volume 123:Issue 11(2018)
• Page Start: 8180
• Page End: 8202
• Publication Date: 2018-11-13
• Subjects: mesoscale -- eddies -- interannual -- decadal -- variability -- Indian Ocean; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2018JC013945
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: A region of elevated mesoscale eddy activity spans the subtropical southern Indian Ocean (SSIO) between Madagascar and Australia. The interannual and decadal changes in eddy activity in the SSIO eddy band, as represented by the variability of eddy kinetic energy (EKE), have implications for the large‐scale circulation, mixed‐layer budgets, and biological activity. An analysis of nearly two and a half decades of sea level anomaly (SLA) data from merged satellite altimetry shows that, in the southeast Indian Ocean east of 90°E, the variations of EKE and SLA are positively correlated on interannual and decadal time scales. Moreover, EKE exhibits a multidecadal increasing linear trend that corresponds to an increasing trend of SLA in the region. The EKE‐SLA covariability in the southeast Indian Ocean does not appear to be associated with a preference for anticyclonic over cyclonic eddy activity; rather, it can be attributed to the common remote forcing from the tropical Pacific associated with the El Niño–Southern Oscillation and the Pacific Decadal Oscillation. In the west central SSIO, wind stress curl just south of the eddy band forces potential vorticity anomalies that affect conditions for instability in the west central SSIO; potential density and potential vorticity gradient anomalies also suggest a remote forcing mechanism originating in the region southwest of Australia. The interannual to multidecadal variability of EKE in the SSIO and its relationship with large‐scale SLA has implications for mixed‐layer dynamics and biogeochemistry and provides a basis for assessment of model simulations of eddy activity in the region. Plain Language Summary: Eddies—rotating storm systems in the ocean—that are formed in the parts of the ocean between the tropics and poleward regions are very important for moving heat, salt, and other substances dissolved in the ocean between the tropics and the poles. An area in the southern Indian Ocean between Madagascar and Australia has particularly high levels of eddy activity, and the energy of the eddies changes substantially over the course of years and decades. To understand why these changes occur, satellite data were used that measure the height of the ocean surface and therefore tell us about the ocean circulation and its variability. This study found that levels of eddy activity near Australia are largely determined by the climate phenomena of La Niña and El Niño. In the central part of the southern Indian Ocean, closer to Madagascar, eddy energy levels are influenced by wind variations locally and ocean conditions in the eastern Indian Ocean. These factors that influence eddy activity in the southern Indian Ocean can help us make better predictions of eddy energy in the region; this will tell us more about how heat, salt, and nutrients are transported between the tropics and the waters near Antarctica. Key Points: Mesoscale eddy activity and sea level in the subtropical southeast Indian Ocean covary on interannual to multidecadal time scales The covariability of sea level and mesoscale eddy activity is caused by common remote forcing from the tropical Pacific In the subtropical south central Indian Ocean, local wind stress and remotely generated subsurface variability force eddy activity