On the dynamics of the seasonal variation in the South China Sea throughflow transport

Abstract

[1] The Luzon Strait transport (LST) of water mass from the Pacific Ocean to the South China Sea (SCS) varies significantly with seasons. The mechanisms for this large variability are still not well understood. The steady-state island rule, which is derived from a steadystate model, is not applicable to seasonal time scale variations in a large basin like the Pacific Ocean. In this paper, we will use a theoretical model that is based on the circulation integral around the Philippines. The model relates the LST variability to changes in the boundary currents along the east coast of the Philippines, including the North Equatorial Current (NEC) Bifurcation Latitude (NECBL), the transports of Kuroshio and Mindanao Currents (KC and MC), and to the local wind-stress forcing. Our result shows that a northward shift of the NECBL, a weakening of the KC or a strengthening of the MC would enhance the LST into the SCS. This relationship between the LST and the NEC-KC-MC is consistent with observations. The analytical result is tested by a set of idealized numerical simulations.

Projected changes of the low‐latitude north‐western Pacific wind‐driven circulation under global warming

“…Results show that this simple model can adequately capture the mean and seasonal cycle of NBL (Figure a). Specifically, the MMM position of NBL and its seasonal migration amplitude are 15.0°N and 0.92°, in good agreement with recent observations and modeling studies [e.g., Yaremchuk and Qu , ; Chen and Wu , ; Yang et al , ; Zhai et al , ].…”

The nascent Kuroshio of Lamon Bay

“…Yang et al . [] find that Kuroshio weakens and Mindanao strengthens as the bifurcation shifts northward and that the westward flow into the South China Sea via Luzon Strait increases. On the interannual time scale, results both from high‐resolution general circulation models [ Kim et al ., ] and from satellite altimetry analysis [ Wang and Hu , ; Qiu and Chen , ] have consistently indicated that the bifurcation latitude of the NEC moves northward during El Niño years, resulting in a minimum transport of the Kuroshio east of Luzon [e.g., Kim et al ., ; Qu and Lukas , ].…”

Spatial structure and temporal variability of the zonal flow in the Luzon Strait

“…Its transport across the observed section attained the peak in January and trough in June, with a peak‐to‐trough amplitude of 2.8 Sv. This seasonal variability is consistent with the annual migration of the North Equatorial Current (NEC) bifurcation, as already noted by previous studies [e.g., Qu and Lukas , ; Qu et al ., ; Yaremchuk and Qu , ; Qiu and Chen , ; Yang et al ., ].…”

“…Based on historical hydrographic data, previous literatures found that the LST has a distinct annual cycle, stronger in boreal winter and weaker in summer seasons [ Wyrtki , ; Shaw , ; Qu , ]. This kind of seasonal variability could be attributed to the seasonally reversing East Asia monsoon [ Farris and Wimbush , ; Metzger and Hurlburt , ; Hsin et al ., ; Wu and Hsin , ], as well as the influence of the boundary current east of the Philippines [ Yaremchuk and Qu , ; Qu et al ., ; Yang et al ., ]. Analysis of altimeter observations and model products also suggested that the LSZF and LST have significant interannual and decadal variabilities.…”