Features and interannual variability of the South China Sea western boundary current from 1992 to 2011

As the largest marginal sea in the western Pacific Ocean, the South China Sea (SCS) is characterized by a mighty current along its northern and western slope, namely, the SCS Western Boundary Current (SCSWBC), which is the most important part of the SCS circulation and plays an essential role in mass, energy and heat budgets in the SCS. Using a new reanalysis dataset of the SCS in conjunction with the observed data, the main features and the interannual variability of the SCSWBC from 1992 to 2011 were studied. Dictated by the prevailing monsoonal winds and in- and outflows, the SCSWBC in winter extended the full length of the western slope and reached its maximum intensity on the southern segment of the western slope off the southeast coast of Vietnam, while in summer the southward flowing WBC was cutoff by the Vietnam Offshore Current and its main body was limited to the northern segment of the western slope. Moreover, the respective seasonal patterns of the SCSWBC showed pronounced interannual variations in its structure, including the axis, the width and the vertical extension. The strength of the SCSWBC, with a mean transport of -11.8 Sv in winter and 1 Sv in summer off the central coast of Vietnam, also differed significantly from year to year, especially for the El Niño years. It was demonstrated that the monsoonal local forcing over the SCS, the interannual variability of which was closely associated with El Niño events, played an important role in modulating the interannual variability of the SCSWBC, whereas the impact of the upper-layer Luzon Strait transport was secondary, which was largely limited in the northern SCS with a weak teleconnection to the southwestern corner of the SCS deep basin.