前人研究結果表明，西南季風與Madden-Julian oscillations (MJO)共同作用的大尺度條件下，莫拉克(Morakot)颱風（2009）在台灣登陸後停滯超過十五小時，給台灣南部帶來嚴重的災害。本文利用可變解析度（60-15 km）全球模式Model for Prediction Across Scales (MPAS) 探討不同時間尺度的季風環流對莫拉克颱風移動路徑的影響。模式的初始場取自ERA-interim的再分析資料，分離出三個不同時間尺度的分量，分別為綜觀尺度（SYN）、準雙週（QBW）以及MJO分量。
為了探討這三個分量各自對莫拉克路徑的影響，本研究設計了敏感性實驗。實驗結果表明，當初始環境場移除QBW和MJO兩個季風分量，莫拉克向西移動越過台灣，並且沒有北轉。當初始環境場的MJO分量增加50%，台灣東南部出現較強的南風和東南風異常，從而導致莫拉克相較實際觀測提早往北移動。在控制實驗中，莫拉克颱風路徑介於MJO強度分別增加和減少50%的路徑之間，顯示莫拉克向西移動與季風環流的連結作用是導致其向北移動的主要因素。
本文亦探討MJO對梅姬(Megi)颱風（2009）路徑的影響。模擬結果與上述莫拉克路徑結論一致，當模式初始場移除MJO分量後，原本北轉的梅姬颱風在登陸菲律賓後，繼續向西移動，並在中國海南島北部二次登陸。

This study uses the global MPAS Model at variable 60-15 km resolution to investigate the interaction between the Typhoon Morakot (2009) and the large-scale environmental flows. Three components of different time scales are filtered from ERA-interim for the model initial fields, namely the synoptic-scale (SYN) mode, quasi-biweekly (QBW) mode and the Madden-Julian oscillations (MJO) mode. To investigate the individual effect of multi-time-scale flows on the evolution of Typhoon Morakot, sensitivity experiments are conducted. Compared to the WRF simulations with different resolutions, the simulation of the TC movement is better for the control experiment, especially the northward turn after making landfall. In the absence of larger-scale monsoonal flow (no_QBW and no_MJO), the simulated Morakot in general takes a quite westward track across Taiwan, without the observed northward movement after landfall. On the other hand, there exists southwesterly wind anomaly from South China Sea to the vicinity east of Taiwan in the Western North Pacific when the intensity of MJO component in the initial field is enhanced by 50%, thus resulting in a north turn of Morakot at a much earlier time than the observed. The simulated Morakot track under the intact MJO component lies in between MJO+50% and MJO-50% experiments, which suggests that the coalescence of Morakot with the monsoonal flow may be intimately related to its north turn after landfall.
The MJO on the track of Typhoon Megi also shows similar impacts as in Morakot. In the absence of MJO, the simulated Megi in general takes a westward movement after passing over the Philippines without turning north.

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