Geostrophic Circulation in the Tropical North Pacific Ocean Based on Argo Profiles

Abstract

Absolute geostrophic currents in the North Pacific Ocean are calculated from the newly gridded Argo profiling float data using the P-vector method for the period of 2004-11. The zonal geostrophic currents based on the Argo profile data are found to be stronger than those based on the traditional World Ocean Atlas 2009 (WOA09) data. A westward mean geostrophic flow underneath the North Equatorial Countercurrent is identified using the Argo data, which is evidenced by sporadic direct current measurements and geostrophic calculations in history. This current originates east of the date line and transports more than 4 3 10 6 m 3 s 21 of water westward in the subsurface northwestern tropical Pacific Ocean. The authors name this current the North Equatorial Subsurface Current. The transport in the geostrophic currents is compared with the Sverdrup theory and found to differ significantly in several locations. Analyses have shown that errors of wind stress estimation cannot account for all of the differences. The largest differences are found in the area immediately north and south of the bifurcation latitude of the North Equatorial Current west of the date line and in the recirculation area of the Kuroshio and its extension, where nonlinear activities are vigorous. It is, therefore, suggested that the linear dynamics of the Sverdrup theory is deficient in explaining the geostrophic transport of the tropical northwestern Pacific Ocean.

On the Formation Dynamics of the North Equatorial Undercurrent

“…Our results show that the NEUC jets extend below a depth of 1500 m, which is also consistent with the observations (Qu et al 1998;Yuan et al 2014;Zhai et al 2013). The maximum volume transport of the NEUC between 88 and 188N in a year is ;9 Sv in the western and central tropical Pacific and decreases eastward, which is much weaker than that of the NEC (Fig.…”

“…5c). The multiple NEUC jet phenomenon and their poleward deepening are also shown by the geostrophic velocity derived from observational temperature and salinity profiles (Qiu et al 2013b;Wang et al 2015;Yuan et al 2014). Although the alternating NEUC jets have been confirmed by many observations and model simulations, their widths, strengths, and the number of the jets below the NEC remain uncertain.…”

“…The NEC in the upper 500 m or so carries subtropical warm water westward and feeds into a higher latitude through the KC. Meanwhile, the subsurface current, namely, the North Equatorial Undercurrent (NEUC; Wang et al 1998), transports intermediate water eastward with a maximum velocity ranging from 0.02 to 0.05 m s 21 (Qiu et al 2013b;Qu et al 1998;Wang et al 2015;Yuan et al 2014;Zhang et al 2017). Although the NEUC is much weaker than the wind-driven NEC, it substantially affects the transport of the intermediate water across the WPO.…”

Mooring observations of equatorial currents in the upper 1000 m of the western Pacific Ocean during 2014

“…The westward‐flowing North Equatorial Subsurface Current (NESC) underneath the NECC has only recently been proposed by Yuan et al . [] based on absolute geostrophic calculations. The NESC is located between 3°N and 7°N over 200–600 m with a mean velocity of 2 cm s −1 at 140°E.…”

Variability of the Pacific North Equatorial Current from 1993 to 2012 based on a 1/8° Pacific model simulation

“…Previous studies have paid much attention to the temporal and spatial variability of the NEC [e.g., Wyrtki , ; Nitani , ; White and Hasunuma , ; Hu and Cui , ; Qiu and Joyce , ; Qiu and Lukas , ; Qu et al ., ; Kim et al ., ; Yaremchuk and Qu , ; Qiu and Chen , ; Zhai and Hu , ; Yuan et al ., ]. At the seasonal time scale, although the NEC bifurcation latitude varies noticeably, variation of the NEC transport is insignificant based on both observations and numerical model results [ Wyrtki , ; Qiu and Lukas , ; Yaremchuk and Qu , ].…”