Wind Modulation of Small-scale Plumes From Yin-Yang Bay


The unsteady behavior of small-scale plumes emanating from Yin-Yang Bay northeast of Taiwan is dominated by winds, tides and the river (the Lien-Tong Stream) forcing. The three-way interaction is examined here using a three-dimensional primitive-equation model, complementing the earlier tide-plume interaction model for Yin-Yang Bay (Lin et al., 1994). Unlike large-scale plumes, whose wind-induced dispersal primarily follows Ekman drifts, small-scale plumes are dispersed by winds in primarily the windward direction. One exception is that a landward wind compresses plume water shoreward and subjects its eventual dispersal to tidal advection and density forcing. Among winds from all directions, seaward winds are found to be the most effective in dispersing plume water afar. It is argued that wind-induced coastal sea level set-up or set-down always acts to offset Ekman drifts and keeps the current windward. This explains why the wind modulation of small-scale plumes is so different from that of large-scale plumes.

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