Identification of different types of Kuroshio intrusion into the South China Sea

Abstract

Kuroshio intrusion into the South China Sea (SCS) has different forms. In this study, a Kuroshio SCS Index (KSI) is defined using the integral of geostrophic vorticity from 118°to 121°E and from 19°to 23°N. Three typical paths (the looping path, the leaking path, and the leaping path) were identified based on the KSI derived from the weekly satellite Absolute Dynamic Topography from 1993 to 2008. The KSI has a near normal distribution. Using ±1 standard deviation (σ) as the thresholds, the leaking path is the most frequent form with the probability of occurrence at 68.2%, while the probabilities of occurrence for the looping path and the leaping path are 16.4% and 15.4%, respectively. Similar analysis is also conducted on the daily Hybrid Coordinate Ocean Model (HYCOM) Global Analysis from 2004 to 2008. The results are generally consistent with the KSI analysis of the satellite data. The HYCOM data are further analyzed to illustrate patterns of inflows/outflows and the maximum/minimum salinity as representatives of the subsurface/intermediate waters. The Kuroshio bending and the net inflow through the Luzon Strait reduce from the looping path to the leaking path to the leaping path. However, the Kuroshio subsurface water intrudes farthest into the SCS for the leaking path. Vorticity budget associated with the different intrusion types is then analyzed. The tilting of the relative vorticity, the stretching of the absolute vorticity, and the advection of planetary vorticity are important for the change of vorticity, whereas the baroclinic and frictional contributions are three orders smaller.

Comparison and validation of global and regional ocean forecasting systems for the South China Sea

“…1, the Kuroshio intruding the SCS through the LUS has been distinguished by three types as the looping path, the leaking path, and the leaping path, according to Nan et al (2011a). All three results show the looping path in winter, the leaping path in summer, and the leaking path in fall, which is well consistent with the model results shown by Wu and Chiang (2007).…”

“…As pointed out in Hu et al (2000), there were four main features of the Kuroshio intrusion as follows: a direct branch from the Kuroshio (Williamson, 1970;Fang et al, 1996;Chern and Wang, 1998;Qu et al, 2000), a form of loop (Zhang et al, 1995;Liu et al, 1996;Farris and Wimbush, 1996), a form of extension (Hu et al, 1999), and a form of ring (Li et al, 1998a, b) at present. Nan et al (2015) reviewed and summarized the Kuroshio intruding processes from observed data, numerical experiments, and theoretical analyses, and concluded that there were three typical paths of the Kuroshio intruding the SCS, the looping path, the leaking path, and the leaping path, which could be distinguished quantitatively by a Kuroshio SCS Index (Nan et al, 2011a) derived from the integral of geostrophic vorticity southwest of Taiwan. The three paths can change from one to another over several weeks.…”

Evolution of an anticyclonic eddy southwest of Taiwan

“…On the other hand, by using AVHRR SST and drifters data, Farris and Wimbush (1996) and Centurioni et al (2004) found that the intrusion of the Kuroshio water into the NESCS occurred most frequently during October and January, and Nan et al (2011b) also pointed out that the Kuroshio intrusion is stronger in winter by using satellite ADT and HYCOM global analysis data. The time of enhanced Kuroshio intrusion is coincident with the period when the AE southwest of the Taiwan is often observed.…”

Eddy formation and surface flow field in the Luzon Strait area during the summer of 2009

“…Yuan et al (2006) demonstrated that the anticyclonic intrusion of the Kuroshio is a transient phenomenon rather than a persistent circulation pattern in the Luzon Strait. Nan et al (2011a) defi ned the Kuroshio SCS Index for the fi rst time to quantitatively distinguish the Kuroshio intrusion as three main types: looping, leaking and leaping using altimetry data and HYCOM model results. At the present time, arguments are unresolved regarding how the Kuroshio intrudes into the SCS and what mechanisms control the variability of intrusion patterns.…”