辛樂克颱風(2008)降雨系集模擬與分析-卡爾曼濾波器資料同化

Ensemble simulations of rainfall in Typhoon Sinlaku (2008) based on EnKF data assimilation

林詩潔(Shih-Chieh Lin)

指導教授 ： 吳俊傑

國立臺灣大學/理學院/大氣科學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.03155

摘要

由於颱風與台灣地形複雜的交互作用，颱風在台灣地區的降雨為模擬與預報上面臨的一大難題。2008年辛樂克颱風為台灣帶來了大量的降水也帶來了許多災害，同時辛樂克颱風恰逢T-PARC ( THORPEX-Pacific Asian Regional Campaign ) 觀測實驗計畫期間，本研究便是利用T-PARC實驗期間豐富的觀測資料搭配新的資料同化技術─ensemble Kalman filter ( EnKF ) 同化颱風的中心位置、移速、渦旋結構等建構出一組高解析度且靜力平衡的資料作為初始場，進行針對辛樂克颱風登陸期間的系集預報與模擬。
28個系集成員間的模擬結果有不小的差異，顯示模式中有許多的不確定性，而初始場為28個系集成員之平均所模擬出的結果便足以代表所有系集成員的平均狀態，不僅如此，其路徑、強度、與降雨形態皆與觀測一致。分析28個系集成員的降雨模擬後可發現，模擬路徑接近觀測路徑的系集成員所模擬出的降雨形態在空間上和時間上的變化皆與觀測一致，降雨量則是有些低估；而偏向觀測路徑西南方的系集成員所模擬出的累積降雨頻率變化雖與觀測相近，但其降雨形態與觀測則不相同且降雨量也是高估許多。當模式解析度提高到一定程度後，再提高解析度，主要對山區的降雨有較大影響，平原地區則沒有太多變化。
此篇研究使用系集預報探討颱風路徑在台灣的降雨形態上扮演著關鍵的角 色，同時也顯示EnKF資料同化方法對於模式初始場的改善，且可反應颱風路徑的變異度，並提供降雨預報的不確定性及可預報度。

關鍵字

系集預報 ； 辛樂克颱風 ； 降雨 ； 卡爾曼濾波器

並列摘要

Forecasting the typhoon-induced rainfall near Taiwan has long been a very challenging issue due to the complex interaction between typhoon circulation and topography of Taiwan. Typhoon Sinlaku (2008), a case in point under The Observation System Research and Predictability Experiment ( THORPEX ) Pacific Asian Regional Campaign ( T-PARC ), with the most abundant aircraft observations taken and with the potential to address major TC issues, produced heavy rainfall over the mountain-area of Taiwan. A newly-proposed vortex initialization method based on the ensemble Kalman filter (EnKF) and the Weather Research and Forecasting (WRF) model is adopted in this study. Taking advantages from the T-PARC data and the new vortex initialization method, this study constructs different ensemble simulations of Sinlaku to investigate the associated precipitation during its landfall period.
The simulated ensemble mean well captures the movement of Sinlaku while there is a wide spread of tracks among the ensemble members. By analyzing all 28 members, the predictability of the rainfall associated with Sinlaku is examined. It is found that members with tracks close to the best track from the CWB are able to present more realistic rainfall distributions ( both temporally and spatially ) though the total rainfall amounts and their cumulative frequencies are underestimated. For members with southward-biased tracks, despite the cumulative frequencies are more similar to the observation, the simulated rainfall pattern is less consistent with the observation and overestimate the maximum of the rainfall amount. When a finer resolution is applied to the simulation, the maximum rainfall amount becomes slightly greater, but the cumulative frequency stays nearly unchanged.
For landfalling typhoons in Taiwan, the track is a critical factor in affecting rainfall simulation. It is important to note that the uncertainties which cause different rainfall patterns or amounts can be addressed from variations among the ensemble members, thus providing more insights into the rainfall predictability associated with typhoons near Taiwan.

並列關鍵字

ensemble simulation ； typhoon Sinlaku ； EnKF ； rainfall

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