Seasonal mean circulation in the Yellow Sea — a model-generated climatology

Abstract

The three-dimensional climatological circulation is computed for the Yellow and Bohai Seas in a series of six bimonthly realizations. The model (QUODDY, Lynch et al., Continental Shelf Res. 16(7) (1996) 875) is nonlinear, tide-resolving, and baroclinic with level 2.5 turbulence closure. Data inputs include seasonal hydrography, seasonal mean wind and river input, and oceanic tides. Results for winter and summer exhibit two distinct circulation modes. In winter, strong northerly wind drives southward flow at the surface and along both Korean and Chinese coasts. This is compensated by deep return flow — the Yellow Sea Warm Current — in the central trough of the Yellow Sea, penetrating to the Bohai. The Changjiang discharge exits to the southwest in winter, trapped along the Chinese coast. In summer, a water mass produced by winter cooling — the Yellow Sea Cold Water — is isolated in the deep central trough, setting up cyclonic circulation over the eastern Yellow Sea. Summer winds from the south drive northeastward flow along the Chinese coast. The net result is a qualitative reversal of the winter pattern. The Changjiang discharge is driven offshore toward the Korean Strait by the summer wind. The winter and summer circulations are partitioned dynamically among tidal rectification, baroclinic pressure gradients, wind response, and river input from the Changjiang. Wind dominates the winter pattern. In summer, baroclinic pressure gradients dominate the eastern Yellow Sea; with wind, tidal rectification, and input from the Changjiang dominant to the west of the cyclonic gyre. The seasonal cycle indicates that January and March exhibit the same basic winter pattern. May is quiescent, followed by July which defines the summer mode. September shows the same general summer pattern, with features shifted westward. November is a transition period followed by winter conditions.