Seasonal variability of the Kuroshio Current at the PN Section in the East China Sea based on in-situ observation from 1987 to 2010

Abstract

As the spatio-temporal variability of the Kuroshio is highly influenced by mesoscale eddies, representing its seasonal variability characteristics requires sufficiently long term observations to reduce the uncertainties. Geostrophic velocity data estimated from hydrographic observation from 1987 to 2010 and the shipboard ADCP velocity data from 1993 to 2008 at the PN Section in the central East China Sea are collected to view the seasonal variability objectively. From both types of observation, it is found that the seasonal climatology mean of the Kuroshio Current exhibits significant difference in three areas, which are located at the Kuroshio Current core and its two flanks in a shallow layer less than 300 m, with the weakest northeast current at the core in autumn, the strongest counter current on the right flank in spring, and the strongest northeast current on the left flank in autumn, respectively. The seasonal variance of the Kuroshio Current also exhibits significant difference on the offshore side of the Kuroshio, with larger variance in spring and summer while smaller variance in autumn and winter. For the current parallel to the PN Section, the ratio of the seasonal variability component to the intraseasonal variability component is relatively smaller than that for the current perpendicular to the PN Section. Further analyses indicate that the seasonal variability at the PN Section is tightly linked to the upstream and downstream current variability.

Future changes to the upper ocean Western Boundary Currents across two generations of climate models

“…Observations suggest that KC strength is weakest during winter, to the east of Taiwan 42 while models and reanalysis display minimum transports earlier in autumn (Figure S1). Further north (28°N) observed transport is minimum in autumn 43 , while the models show no distinct seasonality. In the extension region, surface transport is weakest in winter/spring and strongest in summer/ autumn 44 ; while the model transports tend to peak in spring.…”

The tug‐of‐war between the West Philippine Sea and South China Sea Tropical Waters and Intermediate Waters in the Okinawa Trough

“…The high-salinity WPS Tropical Water (shown in red) is clearly identifiable and does not change very much until near the continental slope where the lower-salinity SCS Tropical Water (shown in purple and blue) is encountered. Except for the autumn (September-November) when the western edge of the WPS Tropical Water is sharp (the vertical yellow and green bands at 125.88E in Figure 5b), there is a lot of interleaving near the shelf break because of various dynamic processes such as wind forcing, thermal winds, mesoscale eddies, internal waves, and tides as well as typhoons [Chang et al, 2010;Guo et al, 2012Guo et al, , 2013Lien et al, 2013;Velez-Belchi et al, 2013;Wei et al, 2015;Wu et al, 2014;Yang et al, 2011Yang et al, , 2012. Yanao and Matsuno [2013] also reported that the partitioning of subsurface waters in the Okinawa Trough into two groups is the most distinct in autumn, but is the least distinct in spring.…”

Seasonal to Decadal Western Boundary Current Variability From Sustained Ocean Observations

“…In the northern hemisphere, the Kuroshio is stronger in the boreal summer, peaking in September (74.7 ± 2.6 Sv), and weaker in the boreal winter, with a minimum in March (64.8 ± 2.5 Sv). Stronger transport in summer has been observed in the upstream Kuroshio (e.g., Gilson & Roemmich, 2002; Lee et al., 2001; Wei et al., 2015; Zhu et al., 2017), though often with minimum transport in autumn (Lee et al., 2001; Wei et al., 2015; Zhu et al., 2017). Observations of the Kuroshio annual cycle near PX40 have not been published before and we find a much larger amplitude than observed further upstream in the Kuroshio.…”

“…We examined seasonal‐to‐decadal variability in the subsurface signature of the Agulhas Current, EAC, and Kuroshio using 16 year time series produced from sustained ocean observations. Few other observational studies of these WBCs span time periods of a similar length or longer (e.g., Beal & Elipot, 2016; Liu et al., 2021; Oka et al., 2018; Ridgway et al., 2008; Wei et al., 2015). Uniquely, our application of a consistent methodology permits direct comparison of velocity and transport variability in the upper 1975 m of WBCs.…”