Influence of Madden-Julian Oscillation on the Intraseasonal Variability of Summer and Winter Monsoon Rainfall in the Philippines

The present study investigates the influence of the Madden-Julian oscillation (MJO) on the intraseasonal variability of summer and winter monsoon rainfall in the Philippines. The monsoon wind-terrain interaction that gives rise to rainfall in the Philippines leads to a sharp contrast between west and east coast rainfall patterns during summer and winter monsoon seasons, respectively. During the summer monsoon season, the eastward-propagating MJO modulates tropical cyclone (TC) activity in the western North Pacific (WNP) on MJO phases 5-7. TC rainfall and remote TC precipitation due to Rossby wave response to TC heating induces strong southwesterly flow that enhances moisture transport and brings anomalous rainfall to the western region of the Philippines. On the other hand, during the winter season, an induced Matsuno-Gill-type pattern to the southeast of the Philippines influences the strength of the Asian winter monsoon. Active (inactive) convection in the tropical Maritime Continent and western Pacific during MJO phases 4-6 produces the anomalous Philippine Sea cyclonic (anticyclonic) circulation. The cyclonic (anticyclonic) anomaly leads to an enhanced (weakened) northeast monsoon flow and wet (dry) rainfall anomaly along the eastern Philippines.