Arterial ocean circulation of the southeast Indian Ocean

Abstract

[1] The time mean ocean circulation for the southeast Indian Ocean (SEIO) is analyzed using a colorwheel to reveal an "arterial-like" structure. Although quasi-zonal, the mean circulation in this region is distinctly more complex than previously presented in recent literature. The mean flow is derived from an eddy-resolving ocean reanalysis of the past 14 years. The ocean state is constrained through data assimilation with observed sea level anomaly, sea surface temperature and in-situ profiles. Geostrophic currents derived from the reanalyzed mean dynamic topography (MDT) are validated against two other MDT analyses to show a comparable arterial structure and distribution of scales. In particular, the broad scale eastward flow is regularly interspersed by narrow bands of the near westward flow. Meridional sections from the ocean reanalysis reveal a net eastward transport in the surface layer and a net westward flow at mid-depth. The seasonality of the surface layer flow in the SEIO appears to have increased (decreased) eastward mean transport that coincide with seasons of stronger (weaker) Leeuwin Current (LC). Whether the narrow bands of mean current and mass flux are simply the average of the eddies or represent an underlying weak jet remains a topic of current debate. Citation: Divakaran, P., and G. B. Brassington (2011), Arterial ocean circulation of the southeast Indian Ocean,

On the Leeuwin Current System and Its Linkage to Zonal Flows in the South Indian Ocean as Inferred from a Gridded Hydrography

“…One source is a southward inflow from the tropics (visible between 1138 and 1148E along the equatorward edge of the plot), which has contributions from the eastward Eastern Gyral Current near 158-208S (Meyers et al 1995;Domingues et al 2007;Menezes et al 2013) and from the shallow flows on the North West Shelf near 208-228S (Wijffels et al 2008). The other is from eastward-flowing interior currents ( jets) offshore from WA (Domingues et al 2007;Divakaran and Brassington 2011;Menezes et al 2014). The strongest of the jets is centered near 248S, and it clearly drives the LC acceleration there.…”

“…In OGCMs with a continental shelf/slope, for which Rossby-wave propagation is inhibited, this mechanism is likely to be significantly modified. As for the overlying eastward flow, the westward flow also tends to organize into jets, and such jets are visible in OGCM solutions (e.g., Domingues et al 2007;Divakaran and Brassington 2011). The cause of westward jets is not clear but is likely linked to that of the overlying eastward ones.…”

“…As a result, the near-surface geopotential height field offshore from WA nearly always decreases toward the south (Thompson 1984;McCreary et al 1986;Woo and Pattiaratchi 2008), driving a continual input of water into the coast. In addition, the eastward flow tends to split into a number of jets (Maximenko et al 2009;Divakaran and Brassington 2011), the most distinctive of which are the tropical Eastern Gyral Current (EGC), which reaches the eastern boundary from 158 to 208S (Meyers et al 1995;Domingues et al 2007;Menezes et al 2013), and the South Indian Countercurrent (SICC; Siedler et al 2006;Palastanga et al 2007), which appears to divide into two branches near 258 and 308S near the WA coast (Menezes et al 2014).…”

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“…The strength of the Leeuwin Current varies seasonally with the ITF strength and interannually with ENSO dynamics, strengthening in winter and under La Niña conditions. The intermediate Leeuwin Undercurrent is derived from an eddy system associated with the Flinders Current near the NP (Middleton and Cirano, 2002;Waite et al, 2007;Meuleners et al, 2007;Divakaran and Brassington, 2011). The Flinders Current and Leeuwin Undercurrent are conduits of the Tasman leakage, a pathway for return flow to the North Atlantic Ocean of deepwater upwelled in the Pacific and a component of the Southern Hemisphere super-gyre that links the subtropical gyres of the Atlantic, Pacific, and Indian Oceans (Speich et al, 2002(Speich et al, , 2007Ridgway and Dunn, 2007;van Sebille et al, 2012).…”

Mean and Seasonal Circulation of the South Indian Ocean Estimated by Combining Satellite Altimetry and Surface Drifter Observations

“…Palastanga et al (2007) accounted the flow structure and variability of the subtropical south Indian Ocean, employing altimetry and model. The south eastern Indian Ocean circulation is noted in Qu and Meyers (2005) and Divakaran and Brassington (2011).…”