台灣寒潮定義－分析以台北測站為代表的適當性

Cold Surges in Taiwan-A Critique of Using Taipei Station Temperature Only to Define the Events

盧孟明(Mong-Ming Lu) ； 李思瑩(Szu-Ying Lee)

《大氣科學》 37卷1期 (2009/03) Pp. 1-10

摘要

寒潮是台灣冬季最重要的天氣現象。儘管過去的台灣寒潮研究多以台北測站資料爲代表，至今尚無文獻說明以單站資料作代表的適當性。本文分析1951至2007年的台北寒潮事件和其它20個氣象站的寒潮發生時間與溫度特性的統計關係，指出以台北寒潮事件作爲其他測站的代表約有50%情況是適當的。寒潮辨識方法乃是根據每一個測站冬季（十一月至次年三月）氣溫與其變化的百分序位所決定的驟降與寒冷的程度決定，驟降的門檻值爲48小時日低溫變化幅度達到該測站百分序位90的變化水準，而寒冷程度的門檻值爲日低溫低於該測站百分序位10的溫度水準。每一測站的寒潮事件都可用「開始日期」、「結束日期」、「長度」、「冷度」、「強度」五個要素描述，台北寒潮與其它測站的關係便可據此統計。結果顯示有80%台北寒潮事件在發生期間有9個以上其它測站也出現了寒潮，而有約50%的比例有17個測站同時出現寒潮。在冷日方面，和台北測站關係較差的有阿里山、玉山、大武、恆春、澎湖五站，而在氣溫驟降方面則以玉山、阿里山、恆春、大武、蘭嶼五站與台北差異較大，顯然中部山區與南部和東南部及離島的冬季氣溫變化有必要與其他區域分開考慮。本文提出的多測站定義優於單站，因可按同時達到寒潮標準的測站數量將寒潮分爲「全島型」與「非全島型」，測站數量低於9站爲「非全島型」，達到17站者爲「全島型」。由於「全島型」與「非全島型」寒潮的大尺度環境條件不同，建議研究台灣寒潮與大尺度氣候關係時宜先濾除「非全島型」寒潮。

關鍵字

寒潮 ； 東亞冬季季風 ； 臺灣氣候

並列摘要

Cold surge is the most important winter weather phenomenon in Taiwan. The conventional definition of cold surge in Taiwan only used daily temperature data at Taipei station. However, the suitability of using one station to represent the whole island has never been documented. In this paper, we propose a new approach that takes 25 meteorological stations into account. The stations are selected because of good quality of the historical data since 1951. Cold surge criteria are based on the ranks of the daily minimum temperature and the 48 hour difference of the daily minimum temperature at each station. When the percentile rank of the daily minimum temperature is lower than the 10(superscript th) percentile and the rank of the 48-hour temperature drop is higher than the 90(superscript th) percentile, the occurrence of a cold surge event is identified. A cold surge event is characterized by five parameters: onset date, retreat date, duration, intensity and coldness. All parameters are determined by the timing and rank of the coldness of the daily minimum temperature and its variations. It is found that about 50% of the overall cold surge events can be represented by the surges at Taipei. The stations less coherent with Taipei, in terms of the ranks of the coldness, are Alishan, Yushan, Tawu, Hengchun, and Penghu. In terms of the ranks of temperature drop, the stations Alishan, Yushan, Tawu, Hengchun, and Lanyu are less coherent with Taipei. These less coherent stations are located either in the central high mountains or near the southern tip of Taiwan. Using the new cold surge definition one can clearly separate the island-wide cold surge events and the sporadic ones by how many stations passes cold surge criteria. This is an advantage for studying the influence of large-scale climate on the winter climate in Taiwan to separate the island-wide and sporadic cold surges.

並列關鍵字

Cold surge ； East Asian winter monsoon ； Taiwan climate