Analysis of Decomposed Surface Currents in a Limited Area

A method of the Helmholtz decomposition for mapped surface currents on grid points is developed. This method is simple, and decomposed currents are not dependent on the distance from the open boundary. This decomposition is applied to surface currents observed by high-frequency (HF) radars. The observation was conducted from April to May 1998 east of Okinawa Island, Japan. The spectral analysis of decomposed currents reveals that the M₂ tidal peak for rotational components is much smaller than that for divergent components, which suggests that the barotropic tidal components are mainly included in divergent currents. The real-vector empirical orthogonal function (EOF) analysis of decomposed currents reveals an embedded eddy, which is related with the convergence of currents