臺灣梅雨季雨型變化與亞洲及西北太平洋夏季風的關係

臺灣梅雨是東亞與西北太平洋夏季季風的一部分。為了解梅雨年際變化與季風的關係，本文以21個中央氣象局局屬測站60年（1960～2019）日雨量資料，計算每候雨量佔梅雨季季總雨量的百分比，定義季雨量在季內的分配曲線為「臺灣梅雨季雨型」。文中提出7個雨型特徵值作為辨識明顯偏離氣候常態異常雨型的判斷依據，其中4項為描述雨型時間特徵的指數，另3項為描述雨型的雨量特徵。時間特徵值分別是梅雨季的開始時間（S）、結束時間（E）、雨期長度（D）、高峰期時間（P），時間單位均為「候」。三個雨量特徵值是梅雨季的峰期雨量（Rp）、前期雨量（Rb）、後期雨量（Rl），雨量單位為日平均雨量（mm/day）。分析結果發現D和S有顯著負相關關係，將全島21個測站的雨型分為西北、東、南三個聚類之後，西北和南部的負相關會更清楚，但東部相關性較弱。4個時間特徵值當中也以D和雨量的關係最好，西北聚類在長雨期年看到比較明顯的梅雨間歇期（break），東聚類的長雨期年有總雨量偏低的傾向。特別要注意的是短雨期年因季節內降雨集中，增加了極端降雨事件的發生機會。最後，為顯示梅雨年際變化與季風的關係，選出長雨期雨量偏少和短雨期雨量偏多各三個「異常年」，對照分析兩組大尺度環流的差異，看到長雨期年在梅雨季期間伴隨西北太平洋副熱帶高壓的偏強，有明顯偏乾的梅雨間歇期，南海低壓和太平洋高壓南方雨帶都偏弱；短雨期年西北太平洋副熱帶高壓在梅雨季期間變化較快，伴隨副高的梅雨鋒面和南海低壓和太平洋高壓南方雨帶都能影響臺灣帶來梅雨。本研究顯示欲改進臺灣梅雨季的中長期天氣預報，預報模式必須具備掌握印太亞澳季風區的熱帶和中高緯度環流與對流變化的能力。

關鍵字

臺灣梅雨；東亞季風；亞澳季風；長期天氣預報；月與季預報；臺灣氣候

並列摘要

Taiwan Mei-yu is part of the boreal summer Asian-western North Pacific Monsoon (AWNPM) system. The daily rainfall data at 21 meteorological stations managed by the Central Weather Bureau during the period of 60 years from 1960-2019 are analyzed. The Taiwan Mei-yu Seasonal Rainfall Pattern (TMSRP) is defined as the pentad percentages of the seasonal total precipitation. The yearly TMSRP is described using seven characteristic parameters that consists of 4 temporal parameters and 3 rainfall amount 3 parameters. Significant negative correlation is found between the duration (D) and the staring time (S) of the Mei-yu season. Among 4 temporal TMSRP parameters D shows the highest correlation with rainfall amount. The rainfall intensity during the short-D years tend to be more intense than other years. Finally, in order to illustrate the relationship between Taiwan Mei-yu and the AWNPM evolution, three dry years with abnormally long D and three wet years with abnormally short D are selected for demonstration. It appears that the WPSH is stronger than normal during long-D years, and the rain bands over the South China Sea and the southern rim of the WPSH are weak. On the other hand, during short-D years the Mei-yu frontal rain, the south China Sea Low rain and the rain band over the southern rim of the WPSH all contribute to Taiwan Mei-yu rain. The analysis results suggest that a good atmosphere-ocean coupled model that can reasonably simulate the Indo-Pacific-Asian-Australian summer monsoon evolution is needed to improve the extended-and medium-range Taiwan Mei-yu forecast.

並列關鍵字

Taiwan Mei-yu ； East Asian monsoon ； Asian-Australian monsoon ； long-range weather prediction ； monthly and seasonal climate prediction ； Taiwan climate

國際替代計量

臺灣梅雨季雨型變化與亞洲及西北太平洋夏季風的關係

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