2016年5〜6月為臺灣有測站紀錄資料以來最暖的梅雨季。過去研究指出溫度的變化會直接影響到 大氣熱力不穩定度的改變，進而造成區域降雨特性（特別是午後對流發生頻率）的變化，因此本研究希 望透過觀測資料的分析，深人瞭解2016年臺灣梅雨季的午後對流降雨特性與往年的差異，並找出影響 此變化的機制。主要研究議題包括：（1)瞭解2016年梅雨季午後對流降雨特性（含降雨量、發生頻率、 降雨強度）變化；（2)找出午後對流降雨事件對2016年梅雨季總降雨的貢獻是否與往年不同；（3)探討大 氣環流變化對2016年梅雨季降雨特性可能造成的影響。研究結果發現，與氣候平均(1982〜2016)相比， 2016年梅雨季(1)受熱力不穩定度增加的影響，臺灣午後對流降雨事件發生頻率增加；（2)在水氣輻合減 少的影響下，使得午後對流降雨之日降雨強度減小。整體而言，因受到午後對流降雨事件發生頻率增加 的影響，午後對流降雨對2016年臺灣梅雨季的總降雨量貢獻，比氣候平均明顯增加。相較之下，在副 熱帶高壓異常增強的影響下，梅雨鋒面不易南下影響臺灣，使得2016年臺灣梅雨季鋒面降雨發生頻率 則較往年減少。這些研究成果，有助於瞭解臺灣梅雨季的降雨特性是如何受到氣候變遷的影響。

Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan (manuscript received 30 September 2016 ； in final form 15 November 2016) ABSTRACT During the Meiyu season (May and June) of year 2016, the seasonal mean temperature reaches the record high in Taiwan. Because the change in local temperature refers the change in local atmospheric thermal instability, which is important to the convective afternoon rainfall (hereafter CAR) formation, it is expected that the rainfall characteristics in Taiwan during the 2016 Meiyu season are very different to the climatological mean status. The main objective of this study is to find out how the 2016 Meiyu season rainfall characteristics (especially CAR) in Taiwan have changed in response to the atmospheric thermodynamical changes. Using the data extracted from 21 surface observations in Taiwan, our results showed that for most stations during the 2016 Meiyu season (1) the occurrence frequency of CAR is above normal, in response to the increase in local thermal instability; (2) the magnitude of CAR rate is below normal, in response to the decrease in moisture flux convergence; (3) the CAR's contribution to total rainfall amount is above normal due t o the increase in CAR frequency not the change in CAR rate. Analyses also indicated that the frontal rainfall amount during the 2016 Meiyu season is below normal, mainly due to that the intensification of subtropical high has prevent the Meiyu frontal systems moving southward to affect Taiwan.