Diurnal variation of precipitation observed over Palau in the western Pacific

Diurnal variation of precipitation was investigated over the tropical western Pacific. An observation project over Republic of Palau was carried out from Nov. 2000. Over Palau region, the season can be divided into westerly wind regime and easterly wind regime by using sounding data. Within each regimes, active and inactive phase of convection were defined by using cloud amount data. Diurnal variation of precipitation was most apparent during the active phase of westerly wind regime with nocturnal maximum. During inactive phase of westerly wind regime, diurnal variation had a lesser afternoon maximum. In contrast, diurnal variation was vague during the easterly wind regime. Precipitation properties were differed between two regimes. High intensity and short duration of precipitation were prevailed during westerly wind regime and weak and long duration were observed during the easterly wind regime. The environment had a difference between the active phase of westerly and easterly wind regime. Middle layers were moister during the westerly wind regime. And moist region expanded broadly over the western Pacific during the westerly wind regime. The difference of diurnal variation of precipitation during the westerlies and easterlies in Palau may be influenced by the seasonal variation of precipitation properties and the environment.This study was expanded by using TRMM PR Heating (PRH) grid dataset to tropical western Pacific region around 130 to 140 E. Similar results of diurnal variation of near surface rain were observed. Intensive doppler radar observations were carried out in Palau from Dec. 2004 to Jan. 2005 and from May to July 2005. Diurnal variation of precipitating clouds was also analyzed in this study.