Intraseasonal Variability of the North Equatorial Current Bifurcation Off the Philippines

Abstract

Characteristics of the intraseasonal variability (ISV) of the North Equatorial Current bifurcation latitude (NBL) are analyzed by using both observations and reanalysis data. The maximum amplitude of the ISV of the NBL can reach about 6° of latitude, which almost triples its annual excursion. The NBL shows a broad spectral peak around 50–140 days with the highest peak occurring around 73 days. Both the Madden‐Julian oscillation and mesoscale eddies have a significant impact on its ISV. A case study for a cyclonic eddy indicates that it can transport about 1.5 Sv (1 Sv–106 m3 s−1) waters to the NBL, and the bifurcation shifts northward with an amplitude of about 8° of latitude in 1 month. Meanwhile, the influence of mesoscale eddies on the ISV of the NBL is highly modulated by the interannual variations of the eddy field. Active eddy activities associated with enhanced barotropic and baroclinic instabilities show a large influence on the NBL. The eddy kinetic energy level around the NBL showed a quite diverse character for the 1997–1998 and the 2015–2016 extreme El Niños, with the latter being double or triple that of the former due to the much stronger vertical and horizontal shears. Given the significant impact on the NBL by the individual eddies and the unevenly distributed cyclonic and anticyclonic eddies around the NBL, the effect of mesoscale eddies on the bifurcation latitude may not cancel each other on seasonal or interannual time scales.

Tracing Organophosphate Ester Pollutants in Hadal Trenches─Distribution, Possible Origins, and Transport Mechanisms

“…Water mass and ocean currents are crucial in determining the distribution of OPEs in the MT seawater . The interaction between atmospheric deposition and oceanic currents plays a differentiated role across various depths: (1) Surface seawater (50 m depth): The North Equatorial Current, which flows from the ocean toward the land, predominantly influences the water mass at this level . Here, atmospheric deposition, through both dry and wet processes, is also a significant contributor to the levels of OPEs in surface waters.…”

“…31 The interaction between atmospheric deposition and oceanic currents plays a differentiated role across various depths: (1) Surface seawater (50 m depth): The North Equatorial Current, which flows from the ocean toward the land, predominantly influences the water mass at this level. 62 Trench and the YMJ. 64,65 These TRWs are known to be linked to a seasonal reversal of abyssal flow from the Philippine Sea to the Mariana Trench.…”

Interannual Variations of the North Equatorial Current Across the Pacific Ocean

“…To answer this question, we calculate the lead‐lag correlations between the transports of MC and NEC‐S (Figure 5a), and between KC and NEC‐N (Figure 5b) across the Pacific basin, respectively. The transport of MC is calculated by integrating southward velocity across 8°N from 130°E to the coast, and the transport of KC is calculated by northward velocity across 18°N (e.g., Kashino et al., 2009; Zhou et al., 2021). As to the NEC‐S and MC, positive correlations are dominant in the whole basin.…”