Cruise Observation of Rossby Waves with Finite Wavelengths Propagating from the Pacific to the South China Sea

This study deals with the physical properties and 3D structures of the wave motions with finite wavelengths of O (100–550) km in the tropical western North Pacific and their variation as propagating from the Pacific to the South China Sea (SCS) using conductivity–temperature–depth observations taken in October and November 2005 and concurrent satellite altimeter data. Three wave components with wavelength bands of O (100), O (200), and O (550) km are derived from the isopycnal undulation signals along 21°, 18°, and 15°N using the ensemble empirical mode decomposition analysis. Their maximum amplitudes are over 100 m in the layer of 1000–2000 m. Phase speeds are derived from cruise-observed vertical profiles of zonal-mean geostrophic flow velocity and the Brunt–Väisälä frequency based on linear quasigeostrophic wave theory with background flow and topography. The speeds are also derived from concurrent sea level anomaly data with the objective Radon transform method. They are close to that of the first baroclinic mode of theoretical solutions, implying that the observed wave motions possess the physical properties of Rossby waves (RWs). The vertical structures of the first generalized modes are derived from cruise observations at three sections. It is shown that the RWs continuously propagate from the Pacific to the SCS, and the available potential energy of RWs 1 and 2 intensify 3–4 times in the Luzon Strait and the SCS compared to that in the Pacific.