A Numerical Study of Currents, Heat Advection, and Sea-Level Fluctuations in the Yellow Sea in Winter 1986

Abstract

A vertically integrated model that incorporates horizontal temperature variations is used to study the circulation of the Yellow Sea in a wintertime period for which velocity and temperature measurements are available at several moorings locations along a central trough. The model features realistic bottom topography and is forced with wind stress and heat flux fields from 13 January to 22 February 1986. The model also incorporates, as a boundary condition, sea-level fluctuations derived from coastal and insular tide gauge stations along model boundaries in open waters. The model reproduces well sea level fluctuations along the coasts of both China and Korea. The hindcast velocity time series, particularly for the north?south component, track those obtained from direct measurements at the moorings. The model momentum balance indicates that the northward flow in the trough is driven by a sea level setup to the south in response to northerly wind bursts in the winter monsoon. The sea-level fluctuations propagate around the Yellow Sea embayment in a counterclockwise sense and exhibit a northward increase in amplitude along both the China and Korea coasts, apparently due to the general shallowness of the northern reaches of the embayment. The lack of a suitable initial condition in temperature and the presence of large biases in the sea surface heat flux distribution preclude the hindcast of the temperature field. Yet trajectories of model fluid displacement confirm an overall northward transport of mass, and hence heat and salt, even though the northerly wind-pulse-dominated current fluctuates with a small mean. While wintertime currents in the Yellow Sea appear dominated by the wind forcing, empirical orthogonal function analysis of model sea-level fluctuations attributes 48% of the variance to a mode whose time variation follows those of sea-level heights imposed along the open model boundaries. The mode with a time variation similar to that found in the wind stress magnitude time series accounts for only 28% of the variance. This suggests the domination of sea-level fluctuations by low-frequency fluctuations in the Kuroshio.