30-60天季內振盪現象對臺灣夏季降雨特色的影響

This study investigates the influence of the 30~60 day intra-seasonal oscillation on the characteristics of summer (June to August) rainfall in Taiwan during 2007~2015. Analyses focus on the changes of rainfall types in Taiwan for the stronger Madden-Julian oscillation (MJO) events (defined as MJO index greater than 0.9). Results show that Taiwan has less precipitation when MJO is in phase 2 (i.e. the active convections located over the middle tropical Indian ocean), and has more precipitation when MJO is in phase 6 (i.e. the active convections located over the tropical Pacific Ocean). Diagnoses show that affected by the intensification of western Pacific subtropical high and the intensification of island-scale diurnal circulation, the percentage of diurnal convection events to the total rainfall events is larger in Taiwan when MJO is in phase 2 than in phase 6. In contrast, due to the intensification of monsoon trough and the intensification of southerly moisture supply over the East Asian-western North Pacific region, both (1) the percentage of tropical convection events to the total rainfall events and (2) the intensify of typhoon type of rainfall are larger in Taiwan when MJO is in phase 6 than in phase 2. These findings can help us understand how the 30~60 day intra-seasonal oscillation identified by the MJO index impact on the characteristics of summer rainfall in Taiwan.