Winter Counter-Wind Transport in the Inner Southwestern Yellow Sea

Coastal currents generally flow downshelf with land on the right side (Northern Hemisphere)
under the geostrophic balance, and are often strengthened by downwelling-favorable winds. However, the
recent mooring observation in the inner southwestern Yellow Sea showed that coastal transport direction
can be substantially changed by tidal forcing. In the survey, the tidal-averaged transports at two out of three
sites remained northward (i.e., in the upshelf direction) and opposite the downwelling-favorable northerly
wind, except during a brief neap tide period. Numerical experiments showed that the incoming Poincar!e
wave tide from the East China Sea plays a key role in forming this counter-wind transport system. This tidal
wave produces a shoreward tidal stress south of 33.58N in the inner southwestern Yellow Sea, driving an
upshelf transport under the Earth’s rotation. Counterpropagating tidal waves from the East China Sea and
the northern Yellow Sea collide in coastal water in 32.5–348N, which produce a standing tidal wave and
therefore a mean sea-surface setup with alongshore and cross-shelf scales of both >100 km. This seasurface
setup causes an alongshore sea surface gradient, which veers the upshelf transport to the offshore
direction under geostrophic balance. The strong tidal current increases the tidal-mean bottom resistance in
the SCW, thus reduces the wind-driven current to a magnitude smaller than the tide-induced residual transport
velocity. Therefore, upshelf transport persists in the inner southwestern Yellow Sea, and the Changjiang
River Estuary becomes a major source area for the inner southwestern Yellow Sea.
Journal of Geophysical Research: Oceans
Hui Wu, Jinghua Gu, and Ping Zhu