Rossby Waves propagating from the Pacific to the South China Sea derived from cruise observations in 2005

Using conductivity-temperature-depth (CTD) observations in 2005 and the simultaneous satellite altimeter data, this study investigates the characteristics of the Rossby waves (RWs) with finite wavelength in the subtropic western North Pacific Ocean (NPO) and their evolution as propagating to the South China Sea (SCS). The first three intrinsic mode functions (IMFs) with wavelength bands of O(100 km), O(200 km) and O(550 km) are derived from the empirical mode decomposition (EMD) analysis of the isopycnal oscillation signals along zonal sections of 21°, 18° and 15°N. The three IMFs are interpreted as three RW horizontal modes (H-modes). RW H-mode 3 with the wavelength of O(550 km) is the most energetic one of the three modes and has the maximum average amplitude of 50 m. All the RW H-modes propagating from the NPO to the SCS are intensified near the western boundary of the NPO with the maximum amplitudes as large as O(100 m) in layers of 1000-2000 m. In the Luzon Strait, the amplitudes of RW H-modes 1 and 2 increase from 80 and 60 m to 100 and 80 m and the Rossby deformation radius decrease from 65 km to 50 km, respectively. The vertical mode (V-mode) decomposition results indicate multi-vertical modes have contributions together to the vertical structure of RW H-modes in the NPO. The dispersion relations of three RW H-modes are derived from cruise observations with the first fourth V-modes 0-3 and the satellite altimeter time series sea level anomaly (SLA) products from 2004 and 2007. They coincide each other if a background ground mean flow velocity of -7 cm s^-1 is counted as an important component for the westward propagation velocity of RWs.