Asymmetric response of coastal currents to oscillating alongshore wind stress over a coastal bank

Abstract

Abstract. An asymmetric response of coastal currents to oscillating alongshore wind stress is observed over a coastal bank off the southern coast of Korea. Alongshore currents exhibit consistently larger variability in the western region than in the eastern region. Numerical experiments show that sea level reaches a maximum (minimum) in the western coastal region during westward (eastward) winds, leading to stronger cross-shore sea level gradients under both wind directions. Momentum balance analysis suggests that the alongshore pressure gradient force acts in the same direction as the wind stress in the western region but opposes the wind stress in the eastern region, resulting in a stronger current response in the western region. The asymmetry arises from spatial differences in mass convergence and divergence driven by spatially varying vertically integrated transport over the bank, which is subsequently governed by arrested topographic wave dynamics. This asymmetric mass redistribution leads to energy flux convergence in the western region. Although offshore currents and variations in the wind stress period and magnitude modulate coastal circulation, the qualitative asymmetry persists. These findings suggest that similar current asymmetries may occur in other coastal regions with bank-like geometry. Understanding such asymmetric current responses to wind stress is essential for assessing their potential ecological impacts in coastal bank regions.