Connection of central South China Sea current variability with tropical Rossby waves in the western North Pacific

• Rossby waves transmit through the Philippines into central South China Sea. • Energy transmission pathway is Celebes Sea-Sibutu Passage-Sulu Sea-Mindoro Strait. • Transmitted waves cause sea level and velocity oscillations in South China Sea. This study investigates the connection between the current velocity variations in the central South China Sea (SCS) and westward-propagating tropical Rossby waves in the western North Pacific, using satellite altimeter observations and coastal tide-gauge data supplemented by numerical modeling. This work is focused on the dynamic link between the intraseasonal velocity oscillations observed in the central-eastern SCS in summer 2017 and the Rossby waves that impinge on the east coast of the Philippine Archipelago. Low-pass-filtered satellite sea level anomaly (SLA) data and coastal sea level records suggest that Rossby waves can propagate into the Celebes Sea and Sulu Sea, eventually reaching the central SCS. A three-dimensional, primitive equation model shows that Rossby wave-associated SLA signals transmit through the Philippine Archipelago to the central SCS via the Celebes Sea-Sibutu Passage-Sulu Sea-Mindoro Strait route, with modeled SLA propagation timings that are consistent with the observations. As the Rossby wave reaches the eastern Philippines, approximately one-third of the incident wave energy from a meridional section east of the Philippines (132°E, between 2°N and 15°N) is transmitted into the Celebes Sea and Luzon Strait, whereas approximately two-thirds of the energy is dissipated, transformed, or reflected along the Philippine coast. Approximately 15 % of the energy entering the Celebes Sea passes through the Sibutu Passage into the Sulu Sea, and ∼10 % exits the Mindoro Strait into the central SCS. These suggest that 2−5 % of the incident energy from the western North Pacific transmitted into the central SCS and influences sea level and velocity variations there.