Diurnal to Intraseasonal Precipitation Variation Around the Northwestern Coast of Luzon Island: Results From YMC-BSM 2018 Field Campaign

This study investigates multiscale variability of summer-time precipitation around the northwestern coast of Luzon Island, the Philippines, by analyzing in situ observation data of a field campaign in summer 2018 conducted under the Years of the Maritime Continent-Boreal Summer Monsoon study in 2018 (YMC-BSM 2018) project. It is found that boreal summer intraseasonal oscillation modulates activity of precipitation diurnal cycle, with active diurnal cycle observed only under easterly (offshore) wind conditions in the free troposphere. On the other hand, in the period of westerly winds, quasi-biweekly fluctuation is observed, with two heavy precipitation events. These events are associated with further intensified westerly winds caused by westward-propagating quasi-biweekly oscillations. Day-to-day precipitation variability over land during the two events is associated with the strength of monsoon winds blowing toward the mountain range, which is modulated cooperatively by the quasi-biweekly oscillations and tropical depressions over the South China Sea.