Comment on "Current separation and upwelling over the southeast shelf of Vietnam in the South China Sea" by Chen et al.

In a recent paper, Chen et al. (2012) showed that the offshore current in front of the Vietnamese upwelling area in the South China Sea (SCS) is caused by an encounter of southward buoyancy-driven coastal current and tidal rectified currents from the southwest. These findings seem not in agreement with in-situ observations. The mechanism for the formation of the offshore current has its origin in the inter-annual variability of atmospheric forcing. El Nino Southern Oscillation events modulate the northern position of Inter-Tropical Convergence Zone and the intensity of both, SW monsoon and upwelling. Strong upwelling influences the spatial distribution of characteristic water masses which results in a blocking of the near coastal northward propagation of the plume of River Mekong and the formation of an offshore current.