Observed features of the Halmahera and Mindanao Eddies

Abstract

[1] The structure and variability of the Halmahera and Mindanao Eddies (HE and ME), which are thought to be quasi-stationary eddies, are described based on onboard and timeseries observations in the gateway region of the Indonesian Throughflow (ITF). The HE was found to have a clear anticyclonic eddy structure during all cruises. It tilted northward and/ or westward with increasing depth. The HE mixes waters from the northern and southern hemispheres and transfers this mixed water to the eastern route of the ITF. The HE shifted northwestward in the boreal summer and the cold phase of ENSO (El Niño and Southern Oscillation) and southeastward in the boreal winter and the warm phase of ENSO. In contrast, the ME, with its cyclonic eddy structure, was observed only once and seems not to be a quasi-stationary eddy. It appears in the mean field and is confined above the thermocline. The stationary northward undercurrent, the Mindanao Undercurrent, was also not found at 7 N east of Mindanao, but the northern tip of the HE was found at this latitude.

Evaluating the impacts of the tropical Pacific observing system on the ocean analysis fields in the global ocean data assimilation system for operational seasonal forecasts in JMA

“…The temperature distributions indicate a good agreement on the strength of the Mindanao Eddy among OSE-XBO, OSE-XAF, and OSE-XTT in this time. The high-salinity water advected by NGCUC intrudes across the equator and turns around the Halmahera Eddy positioned at 2°N-133°E as indicated in previous studies (Kashino et al 1996(Kashino et al , 2013. Then, it is advected eastward by NECC while dissipating.…”

“…The Mindanao Dome has a large interannual variability (Tozuka et al 2002;Zhang et al 2012) that is not sufficiently recovered by the OGCM alone, and data assimilation contributes to an improvement in the accuracy in this region. In addition, interaction of the tail of the New Guinea Coastal Undercurrent (NGCUC) with the North Equatorial Counter Current (NECC) and the Mindanao Current induces many small spatial and temporal scale features associated with the Halmahera Eddy and seasonal appearance of other mesoscale eddies (Masumoto et al 2001;Heron et al 2006;Kashino et al 2013). These features seem to be inherently uncertain, and data assimilation probably reduces this uncertainty.…”

Isotopic Evidence for the Evolution of Subsurface Nitrate in the Western Equatorial Pacific

“…Along the northeastern PNG coast, the surface NGCC turns to the east feeding the North Equatorial Countercurrent (NECC), while the underlying NGCUC partly turns eastward feeding the EUC (Bingham & Lukas, ) and partly crosses the equator and diverges into the Indonesian Throughflow or northward along the coast of the Philippines into the Mindanao Undercurrent (Figure c; Qu & Lindstrom, ; Tsuchiya, ). The eastward deflection of the NGCC into the NECC further results in a quasi‐stationary eddy structure called the Halmahera Eddy (HE) northwest of PNG (Fine et al, ; Kashino et al, ).…”

Seasonal eddy kinetic energy modulations along the North Equatorial Countercurrent in the western Pacific

“…migrate northwestward in boreal summer and southeastward in boreal winter [e.g., Heron et al, 2006;Kashino et al, 2013]. Dynamically, much of the seasonal circulation variability has been demonstrated to be induced by the seasonal evolution of the regional monsoonal winds being northeasterly in winter (December-March) versus southwesterly in summer (June-September).…”