Can Luzon Strait Transport Play a Role in Conveying the Impact of ENSO to the South China Sea?*

Abstract

The Luzon Strait transport (LST) from the Pacific into the South China Sea (SCS) is examined using results from a high-resolution ocean general circulation model. The LST from the model has a mean value of 2.4 Sv (Sv ϵ 10 6 m 3 s Ϫ1) and reaches its seasonal maximum (6.1 Sv westward) in winter and seasonal minimum (0.9 Sv eastward) in summer. Both the annual mean and seasonal variation of LST compare favorably with earlier observations. On an interannual time scale, LST tends to be higher during El Niño years and lower during La Niña years, with its maximum (minimum) leading the mature phase of El Niño (La Niña) by 1 month. The interannual variation of LST appears to be oppositely phased with the Kuroshio transport east of Luzon, indicating a possible nonlinear hysteresis of the Kuroshio as a driving mechanism of LST. For the annual average, water leaving the SCS in the south is of higher temperature than that with LST, thus producing a cooling advection in the upper 405 m equivalent to a surface heat flux of Ϫ19 W m Ϫ2. Most of this cooling advection is balanced by the atmospheric heating (17 W m Ϫ2). From late spring to early fall, surface heat flux is the primary heating process; only a small part of the heat content change can be explained by heat advection. But, in winter, heat advection seems to be the only important process responsible for the cooling in the upper layer of the SCS. The interannual variation of the upper-layer heat content has a strong signature of ENSO, cooling in the development of El Niño and warming in the development of La Niña. An oceanic connection is revealed, in which LST seems to be a key process conveying the impact of the Pacific ENSO into the SCS.

Progress of regional oceanography study associated with western boundary current in the South China Sea

“…Existing research has shown that, although the SCS has a climatological warm pool structure [78,79], its SST has significant interannual variation [80], and the interannual variability of the basin-wide SST is different in winter and summer [81]. Through the atmospheric and ocean circulations [82,83], the El Niño and Southern Oscillation (ENSO) signal can affect the oceanic variability in the SCS. The change of mixed layer depth (MLD) is also an important factor that impacts the SST [84], and in turn SST can impact the atmospheric circulation.…”

Regime shift of the South China Sea SST in the late 1990s

“…Northward shift of the NECB during the El Nino years results in weaker Kuroshio Current in east of the Philippines. Subsequent reduction in the potential vorticity enables enhanced penetration of the Kuroshio water through the Luzon Strait Qu et al 2004). Conversely during the La Nina years, the southward shift of the NECB leads to a stronger Kuroshio Current and weaker LST and SCSTF.…”

“…The changes in ocean circulation and sea level associated with the monsoons are identified as the primary forcing mechanism of the SCSTF seasonal variability (Metzger and Hurlburt 1996). Meanwhile, its inter-annual as well as decadal variability are considered to be mainly governed by the ENSO Phenomenon (e.g., Qu et al 2004;Wang et al 2006b;Liu et al 2012). However, recent studies revealed that other large-scale phenomena such as the PDO also have a significant role in determining the low-frequency variability of the SCSTF (Yu and Qu 2013;Nan et al 2015).…”

Upwelling of Pacific Intermediate Water in the South China Sea Revealed by Coral Radiocarbon Record

“…Well-equilibrated water enters through the NEC via the KI, with the main throughflow moving surface water south along the Vietnam coast during the NE monsoon and flowing out through the Java Sea and into the ITF. In the Makassar Strait, the seasonal mixing of surface waters is complex but reflects the relative contribution of source waters from (1) the Indonesian Throughflow (ITF) originating from NEC and South Equatorial Current (SEC) surface and subsurface water, and (2) the South China Sea Throughflow, that enters the SCS from the Luzon Strait and exits it through the straits to the south (Qu et al 2004(Qu et al , 2006. The relative contribution of these two source waters alternate during the SE and NW monsoon ( Gordon et al 2012).…”