Changes in Low-Frequency Variations of Autumn Rainfall in Taiwan

• Main Authors: Lee, Cheng-An, 李正安
• Other Authors: Huang, Wan-Ru
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/q97v89

碩士 === 國立臺灣師範大學 === 地球科學系 === 106 === 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 non-typhoon-related-rainfall. Research topics are divided into three: (1) Is there any change in the time characteristics of low-frequency variations of autumn rainfall in Taiwan? (2) Is there a regional difference in low-frequency variations of autumn rainfall in Taiwan? (3) If there is a change in low-frequency variations of autumn rainfall in Taiwan, what are the possible reasons? In response to the first issue, our results show that the autumn rainfall in Taiwan was dominated by a clear signal of quasi twenty-year oscillation before 1985. After 1990, the oscillation period for the low-frequency variations of autumn rainfall was changed to about 10 years. This phenomenon not only exists in the "total rainfall in autumn" but also in "the typhoon-related-rainfall" and "the non-typhoon-related-rainfall". In response to the second issue, 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. In response to the third issue, our examinations on the related mechanisms show that the changes of High over Asia Continent, 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.