The Role of MC River Discharge on the Propagation of Intraseasonal Oscillations

The Maritime Continent (MC) is comprised of many islands, mountains, and deep and shallow marginal seas. Many rivers in the MC region also discharge a large amount of freshwater from heavy precipitation over the high terrain of the MC islands. In this study we investigate the influence of the freshwater discharge from numerous MC rivers on the northward propagation of boreal summer Intraseasonal Oscillations (ISO). The coupled model used is the NRL Coupled Ocean/Atmospheric Mesoscale Prediction System (COAMPS) coupled with the Navy Costal Ocean Model (NCOM). Preliminary COAMPS-NCOM high-resolution model experiments for an August 2016 ISO event show that the Agno river discharge off the west coast of Luzon, Philippine alters the location of the ISO convection and propagation over the coastal ocean as well as over land. Two COAMPS experiments with and without the river outflow to the ocean indicate a non-negligible sensitivity. The freshwater discharged from the Agno River shifts the ISO convection northwestward and further offshore. The change of the ISO location and propagation in this case is through a complex air-ocean-land interaction and feedback mechanism.