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Student Number 946201009
Author Choi-San Mak(麥翠珊)
Author's Email Address No Public.
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Department Graduate Institute of Atmospheric Physics
Year 2007
Semester 2
Degree Master
Type of Document Master's Thesis
Language zh-TW.Big5 Chinese
Title Impacts of Assimilation of a Virtual Vortex Obtained from MM5 4DVAR on WRF Typhoon Predictions
Date of Defense 2008-06-26
Page Count 115
Keyword
  • Bogus vortex
  • Abstract The discrepancies between model initial analysis and the true state may contribute to the factors for model prediction errors. To adjust the initial fields for reducing the discrepancies, many data, such as satellite observations, are available for assimilation, however still showing less impacts as compared to those from insertion of a bogus vortex. Using a four dimensional variational method (4DVAR), the bogus vortex can be effectively assimilated into the model to adjusts the initial field under constraints of model dynamics, which is the so-called bogus data assimilation (BDA). In this study, we address a new BDA method which adopts the better balanced vortex from MM5 4DVAR than the traditional simple Rankine vortex and then applies the three dimensional variational method (3DVAR) to assimilate this vortex data into WRF to investigate the impacts on track and intensity predictions of typhoons impinging Taiwan.
    The target of this research is to evaluate the impacts of the new method on typhoon prediction. Two typhoons, Shanshan (2006) and typhoon Sepat (2007), were selected in this study, and they were simulated for 72 h. The results show that assimilation of the 3D wind of the virtual model vortex from 4DVAR in general have the largest improvement on typhoon simulation. Besides, the wind field tends to adjust to the mass field in 3DVAR and hence an unreasonable vortex structure may be produced when an unrealistic temperature from BDA has been assimilated as well by 3DVAR. The results also indicate that this assimilation tends to faster the typhoon movement, possibly due to the intensified 3DVAR vortex after the assimilation of the virtual vortex. For simulation of typhoon intensity, this approach may give significant improvement. Sensitive tests show this improvement, however, becomes much less when sea surface pressure was assimilated instead. Assimilation with the combined data (wind, temperature and moisture) in general does not lead to more consolidated improvement.
    Table of Content 中文摘要………………………………………………………...................................i
    英文摘要......................................................................................................................ii
    誌謝.............................................................................................................................iii
    目錄.............................................................................................................................iv
    表目錄…………………………………………………………….............................vi
    圖目錄………………………………………………………....................................vii
    第一章緒論……………………………………………….....................................1
    1-1前言…………………………………………………...............................1
    1-2文獻回顧…………………………………………...................................1
    1-3研究動機……………………………………………...............................3
    第二章研究方法與實驗設計………………………………….............................5
    2-1  資料來源………………………………………….................................5
    2-2  模式簡介……………………………………….....................................5
    2-3  研究方法……………………………………………..............................6
    2-4  實驗設計………………………………………......................................9
    第三章 個案介紹………………………………………………............................10
    3-1 珊珊颱風……………………………………..........................................10
    3-2 聖帕颱風……………………………………...…...................................10
    第四章 結果分析與討論……………………………............................................11
    4-1 珊珊颱風個案分析…………………………..........................................11
    a. 4DVAR BDA後的MM5初始場............................................................11
    b. 3DVAR同化不同參數後之WRF初始場…….....................................12
    c. MM5及WRF模擬的結果……………………….................................14
    4-2 聖帕颱風個案分析…………………………………..............................15
    4-2-1 初始時間為14日00UCT…………................................................15
    a. MM5 4DVAR初始場場及3DVAR WRF初始場….............................15
    b. MM5及WRF模擬的結果 …………………….………...................16
    4-2-2 初始時間為16日00UCT……………………………...................16
    a.4DVAR BDA後的MM5初始場…………………………...………....16
    b.3DVAR同化不同參數後之WRF初始場…...................................…..17
    c.MM5及WRF模擬的結果……………….................………………....17
    4-3 比較各模擬結果的結構差異…………….......................................……18
    a.珊珊颱風spin up結構分析………………............................................18
    b.聖帕颱風spin up結構分析……………...........................................….20
    第五章敏感度測試…………………………………….............................……21
    第六章結論與展望……………………………………….…................………23
    參考文獻………………………………………………..................................……..27
    表…………………………………………………….................…………………...30
    圖……………………………………………………….................………….……..34
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    Advisor
  • Ching-Yuang Huang(黃清勇)
  • Files
  • 946201009.pdf
  • approve immediately
    Date of Submission 2008-07-02

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