Dynamics of surface currents over Qingdao coastal waters in August 2008

Abstract

Surface currents measured by High Frequency (HF) radar are used to investigate the dynamics in the coastal waters of Qingdao, China, on the western coast of the Yellow Sea. Different factors affecting the surface currents are revealed by dynamical analysis. Harmonic tidal analysis shows that the coastal tidal currents are barotropic and their temporal evolution is mainly influenced by the semidiurnal tidal constitutes, topography and geometry. It is also found that their horizontal distribution represents the effect of local topography. At sub-tidal frequencies, the high correlation between winds and the sub-tidal surface currents indicates a crucial role of wind-forcing in driving the currents. Varying wind direction coupled with small-scale features of the coastal geometry results in complicated sub-mesoscale circulation. In addition, the monthly coastal circulation is characterized by an eddy structure and is primarily determined by the outflow which is closely associated with the sea level slope along the coast. The variability of the residual currents is studied by analyzing the cross-shore momentum equation with wind stress, sea level records, and HF radar currents. It is shown that both the barotropic pressure gradient and the nonlinear tidal stress contribute to the variations of the residual currents near the bay mouth and further govern the coastal monthly circulation in August, 2008. Copyright 2011 by the American Geophysical Union.