颱風風雨型態分析辨識與分類氣候法定量推估降雨之研究

Analysis of Typhoon Wind-Rain Relationships And the Assessment of the Typhoon Climatology Rainfall QPF model Integrating Pattern Classification Indicators

林佑蓉(Yu-Jung Lin)

指導教授 ： 李天浩

國立臺灣大學/工學院/土木工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01798

摘要

既有氣候法颱風定量降雨模式推估台灣降雨的推估技術，無法分辨2001年桃芝颱風和2005年海棠颱風兩個路徑類似、降雨分佈卻很不相同的案例。桃芝颱風結構緊實、導引氣流強勁、通過速度快、降雨集中在中心通過路徑兩側，和海棠颱風導引氣流不強、在花蓮外海打轉、速度減緩到滯留，造成颱風環流外擴到台灣北部和南部通過、降雨集中在台灣南部高屏溪等流域上游山區、中部地區降雨反而小。桃芝和海棠颱風降雨分佈型態顯示，路徑類似颱風若結構不同，降雨空間分佈型態未必類似，氣候法將所有類似路徑颱風降雨平均，不同個案推估的定量降雨誤差可能差異很大。
本研究利用路徑類似歷史颱風的風雨觀測資料，建立可以辨識、分類颱風型態的「分類差異距離指標」，區分為型態接近與不同的颱風，排除型態不同的類似路徑颱風，僅利用指標為「類似」的歷史颱風事件計算氣候平均降雨。資料分析使用的方法概要：(1) 利用歷史颱風風雨觀測紀錄資料，觀察颱風與地形交互作用與降雨風場分布，嘗試建立適合作颱風風雨分類的統計指標；(2) 以中央氣象局定義之第二及第三類颱風路徑為分析目標，由歷史颱風統計指標之主成分分析與相關係數統計方法，決定「類似」與「相異」事件的選擇門檻；(3) 將「分類差異距離指標」應用至預報範圍，以主成分分析統計各指標間相關性的結果，檢定類似指標應用的全域性；(4) 改進氣候法降雨推估，僅利用指標為「類似」的歷史颱風事件計算氣候平均降雨，比較改進後的氣候法估計誤差權重平方和與誤差變異係數，並評斷方法的改進效益。
研究證實，「分類氣候法」在特殊降雨分布之颱風案例可能從延時1小時預報開始，預報的誤差變異數就比傳統氣候法高；預報時數增加時，分類氣候法估計颱風降雨的準確度可能更加不如傳統氣候法。而在典型降雨分佈之颱風案例中，雖然傳統氣候法的降雨推估誤差，相對於特殊案例已經較低，分類氣候法依然能夠再降低；龍王颱風過山前的案例改進較有限，但龍王颱風過山後，和聖帕颱風過山前和過山後的三個案例，推估未來1~3小時的改進幅度都相當明顯。對於選擇的8個降雨推估案例：分類氣候法於T=0找到的案例，在台灣北部、東北部的降雨誤差比傳統氣候法小，T=1~3時的誤差持續較小；在中、南、東部的降雨誤差和傳統氣候法相當，T=1~3時的推估值未獲改進。
結果顯示二、三類路徑颱風案例太少，在有限案例中，分類法僅找到台灣北部區域降雨型態比較類似的颱風事件，其他區域降雨型態的歧異程度和傳統氣候法相同。未來若有更多颱風案例，分類法能找到所有降雨區域都和真實降雨類似的案例，則1~3小時的降雨推估有機會更優於傳統氣候法。

關鍵字

颱風 ； 降雨 ； 型態 ； 氣候 ； 統計 ； 定量推估

並列摘要

The assessment of the original typhoon climatology rainfall QPF model cannot analyze typhoons which have similar path but different rainfall pattern such as Toraji in 2001 and Haitang in 2005. Typhoon Toraji has strong atmospheric structure, powerful current lead high speed passing and concentrating rainfall through the way. Typhoon Haitang has opposite atmosphere condition, which has week current lead slow passing. The typhoon center stay at offshore Hualien induce the outer circulation extend to northern and southern Taiwan. Haitang’s rainfall almost concentrated on Kaoping river basin upstream, and less in middle Taiwan. This two typhoon rainfall pattern shows: if similar path typhoon have different structure, the distribution pattern of rainfall would not in the same. The climatology use all similar path typhoon to compute the rainfall average but different case might be has big variation in QPF model.
This research use historical wind and rainfall observation which has similar path to establish the classification indicators that can analysis the wind and rainfall pattern. Include the historical typhoon which has analogous indicators to compute the climatology average rainfall but exclude the different pattern historical typhoon. Data using process as follows: (1) Observe the interaction between typhoon and Taiwan topography, also the wind and rainfall distribution, then use historical wind and rainfall observation to establish the classification indicators. (2) Decide the threshold of similarity and difference, and use PCA method to realize the relation between the indicators. Use type 2 and type 3 typhoon path defined as CWB to be database. (3) Apply the indicators to the predicted area then check out the application of the all predicted region. (4) Improve the Climatology Rainfall QPF, then compute the error square of estimate and the coefficient of variation which is compared with original climatology rainfall QPF method.
This research confirms that error variance of classification climatology might higher than traditional climatology in special rainfall pattern of typhoon begin from lag time is 1; when predict lag time increase, it will not better than traditional climatology. On the other hand, error variance in typical rainfall pattern of typhoon is better than it in special rainfall pattern cases; for 8 cases of rainfall: When lag time is 0 in northern and northeastern Taiwan, the error square of estimate calculated by classification climatology is less than traditional climatology. When lag time is 1 to 3, the error square of estimate is continued small but the error square of estimate is equal to traditional climatology in middle, southern and eastern Taiwan.
In this few cases, classification climatology only can find the similar rainfall pattern cases in northern Taiwan area. The variance of rainfall pattern in other areas is like the traditional climatology. In the future, if we have more typhoon cases, this classification climatology will find all rainfall areas are almost the same with the true rainfall pattern and predict of rainfall will better than the traditional climatology in lag time is 1 to 3.

並列關鍵字

typhoon ； rainfall ； pattern ； climatology ； statistics ； quantitative precipitation forecast

參考文獻

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