臺灣秋季降雨之低頻擾動變遷

This study examines the characteristics of low-frequency variations of autumn (September, October and November) rainfall in Taiwan, during 1945-2015. Analyses focus on the contribution of rainfall from two different types: the typhoon-related rainfall and the nontyphoon-related rainfall. By applying the 5-year running mean analysis on the autumn rainfall, our results showed that the autumn rainfall in Taiwan was dominated by a clear quasi twenty-year oscillation signal before 1985. After 1990, the oscillation period for the low-frequency variation of autumn rainfall was changed to about 10 years. By analyzing the rainfall data from 10 stations of the Central Weather Bureau during 1945-2015, we found that the above phenomenon of low-frequency variations is an island-wide phenomenon. Although the amplitudes of the oscillations vary from place to place, the oscillation period of autumn rainfall is similar for all examined stations in Taiwan. Further examinations on the issue of "What climatic factors affect low-frequency variations of autumn rainfall in Taiwan?" show that the changes of "continental high over China", "Pacific subtropical high", and "moisture flux" are three of important factors affecting the changes in the oscillation period of autumn rainfall (including typhoon-related and non-typhoon-related rainfall) in Taiwan.