Browsing by Author "Tseng, Li-Shan"

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    How much of Typhoon Morakot’s extreme rainfall is attributable to anthropogenic climate change?
    (International Journal of Climatology, 2019-06-30) Wang, Chung-Chieh; Tseng, Li-Shan; Huang, Chien-Chang; Lo, Shih-How; Chen, Cheng-Ta; Chuang, Pi-Yu; Su, Nan-Chou; Tsuboki, K.
    Typhoon Morakot (2009), which made landfall in Taiwan during August 7–9, 2009, produced the highest rainfall and became the deadliest typhoon ever recorded in Taiwan since 1958. To assess the role of anthropogenic climate change in the typhoon‐related torrent, we compare the water budget between a pair of cloud‐resolving sensitivity experiments. The pair consists of a control simulation that reproduces Typhoon Morakot (2009) in current climate and a sensitivity simulation in which the same storm is placed in a slightly different climate background where the late 20th century anthropogenic climate change signal is removed. The anthropogenic signal is estimated with the CMIP5 experiments of 18 models for the period of 1985–2005, during which the global warming trend is discernible. In climate states that differ merely by a 20‐year mean anthropogenic change, Morakot (2009) yields 3.4–3.6% more total rainfall in the control experiment than its sensitivity counterpart within a radius of 300–500 km from the storm centre. Water budget analysis indicates that the increase in typhoon rainfall is mainly resulted from the enhanced convergence of vapour flux. The enhancement is, in turn, contributed by the increased tropospheric moisture due to global warming and, to a lesser extent, by a more active secondary circulation in the storm that is associated with the anthropogenic climate change.
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    冬季西伯利亞高壓移動路徑之分析及其對臺灣寒潮之影響
    (2020) 陳亭安; Chen, Ting-An
    影響東亞地區冬季期間最主要的系統即為西伯利亞高壓，了解與其相關之 高壓的移動路徑為了解東亞地區冬季氣候變化的重要工作之一。為提高研究的 科學再現性，並免除過去主觀追蹤高壓移動路徑的種種不便，本研究使用再分 析資料，經一系列演算法客觀的定義 1948—2017 年間東亞地區高壓移動路徑， 並依其主要行經位置將路徑分為向東移動進入西伯利亞高壓區的西側路徑 (West Tracks)，及自西伯利亞地區發源，並向東移動的東北路徑 (Northeast Tracks)，和東南路徑 (Southeast Tracks) 三類。 經分析後發現 1983—2017 年間，Northeast Tracks 和 Southeast Tracks 的數 量皆較 1948—1982 年間多，但 West Tracks 的數量則以 1948—1982 年間較多。 此外，Southeast Tracks 的數量和西伯利亞高壓強度呈現負相關，當西伯利亞高 壓較弱時，較容易自高壓東南方分裂並形成一向東移動之子高壓。 從天氣尺度上來看，長短不一的寒潮事件為東亞地區冬季期間最常見的天 氣現象，當北方冷空氣經由西伯利亞高壓傳至南邊使該地降溫時即可能發生。 冷空氣南傳的方式主要可分為二種，西伯利亞高壓受其東北方阻塞高壓影響滯 留原地，冷空氣隨高壓東側北風持續南傳使華中及華南地區降溫;另一種冷空 氣南傳的方式為西伯利亞高壓向東南方延伸或分裂子高壓時帶至行經區域令該 地降溫形成寒潮。 為瞭解客觀分析之路徑與臺北地區寒潮間關聯，將 2000—2017 年間臺北所 發生之五十六次寒潮事件依地面氣溫、地面氣溫降溫速率、阻塞高壓存在與否 分成三類: (1) 第一類寒潮(blocking with cold air and temperature drop, BCD)，十 八年間共發生二十五次; (2) 第二類寒潮(blocking with cold air only, BC)，十八 年間僅發生五次; (3) 第三類寒潮(cold air and temperature drop without blocking, CD) ，十八年間共發生二十六次。第一、三類寒潮事件臺北地區皆快速降溫， 其間伴隨 Southeast Tracks 的機率約為 80%，比第二類寒潮事件多了約 20%。