冬季東亞季風與台灣氣候即時監測分析：2010～2013年實例

East Asian Winter Monsoon and Taiwan Climate Real-time Monitoring and Analysis Applied to 2010-2013 Winters

李思瑩(Szu-Ying Lee) ； 盧孟明(Mong-Ming Lu)

《大氣科學》 42卷2期 (2014/09) Pp. 87-112

摘要

台灣冬季氣候主要受東亞冬季季風系統（East Asian winter monsoon，EAWM）控制，監測分析和預報季風特徵是氣象服務的重要一環。本文以2010～2013年為例，說明氣象局〈災害性天氣監測與預報作業建置計畫〉發展的EAWM監測方法。運用2個以季風低層變數設計的指數和2個高層變數指數，從季風的季節平均、季內變化、年際變化三種觀察角度，說明如何以「強度」、「弱度」、「變異度」為評量指標簡要描述每一年的季風特徵。「強度」是僅計算正距平季風指數的平均距平值，「弱度」則是僅計算季風指數出現負距平的日數，「變異度」是以每年冬季（10～3月）為計算期限的季風指數變異數。季風的相對強弱與變化幅度判斷標準以世界氣象組織規範的30年氣候基期為準，每10年更新一次。以2010～2013年為例，以1981～2010年氣候基期為參考，根據「強度」可判斷2011年為強季風年，根據「弱度」可判斷2013年為弱季風年，而根據「變異度」可判斷2011年為季風變異超乎尋常的氣候異常年，這一年的季風變異度相對於氣候基期的統計數據是一個離群值（outlier）。根據不同的季風指數，可看到2011年的異常現象以中高緯區域為主，將熱帶風場納入計算的季風指數並沒有異常的現象。本文提出的監測方法適用於任何季風指數，未來可挑選更多可反映季風不同特性的指數，豐富東亞冬季季風與台灣冬季氣候即時監測分析的內容。

關鍵字

東亞冬季季風 ； 臺灣氣候 ； 季風指數 ； 氣候監測

並列摘要

Taiwan winter climate is mainly influenced by the East Asian winter monsoon (EAWM) system. Monitoring and analyzing EAWM is an important item in national meteorological services. The present study uses the winters of 2010-2013 as examples to present the monitoring and analysis methods developed in ＂CWB's Hazardous Weather Monitoring and Forecasting Systems Enhancement Project＂ (2010-2015). The analysis is focused on three monsoon aspects: the seasonal mean, intraseasonal and interannual variations represented by two EAWM indices based on the low-level atmospheric variables and two indices based on the upper-level atmospheric variables. The metrics used to quantify the characteristics of monsoon variability are the monsoon strength, weakness, and variance. Monsoon strength (weakness) is calculated by the sum of the positive (negative) anomalies on the daily basis of a monsoon index. The monsoon variance is simply calculated by the variance within 6 months of the winter half year of a monsoon index. The relative intensity and variability of the monsoon in any particular year is compared with the data of 30-year climate following the WMO guideline for operational meteorological services. Results of the analysis of the 2010-2013 monsoons of the present study suggest that 2011 is an extreme winter in terms of its intraseasonal variability. The variance of 2011 EAWM is an outlier of the 30 variances of 1981-2010. However, the extreme phenomena is mainly influences by the high-latitude variability, because the variances of the EAWM indices that include the low-latitude variables are not outliers of the 30-year climatology. The analysis method proposed in this study can efficiently integrate the measurements represented by different EAWM indices and enrich the real-time climate monitoring and analysis information over East Asia and Taiwan.

並列關鍵字

East Asian winter monsoon ； Taiwan climate ； Monsoon index ； Climate monitorin