| 摘要: | 本論文為台灣第一篇使用單都卜勒雷達風場反演方法 ， 搭配相位陣列式氣象
雷達資料來進行分析的研究，目的在探討使用高速掃描的雷達資料所分析出來的
風場的特性，並驗證之前從理論上對單雷達反演法運算表現的若干預測是否為真。
本篇論文的研究方法是藉由單都卜勒雷達所觀測到的回波及徑向風資料，將
完整的三維風場反演出來。此方法先計算出一組隨高度變化的最佳移速(U, V, W) ，
而相對於此最佳移速的擾動風場(u′, v′, w′ )再經由極小化一價值函數透過三維變
分法求得，最後將此擾動風場加上最佳的移速後，即得到完整的三維風場。
本文先實行一 OSSE(Observation System Simulation Experiment)實驗，模擬一
理想的濕熱胞，檢驗在不同時間解析度情況下反演出來的風場品質，結果顯示在
不同時間解析度下的反演結果與模式模擬的結果具有良好的一致性，並且增加時
間解析度能夠提升反演出來風場的品質。
接著本文選取 2009 年 6 月 5 日在美國實行的 VORTEX2 龍捲風暴觀測實驗，
使用其中一座相位陣列式雷達(MWR-05XP)以及兩座移動式都卜勒雷達 DOW6
和 DOW7 的觀測資料，對此反演法進行測試與驗證。其結果顯示在不同時間解
析度下三個雷達都分別可以把龍捲風暴鉤狀回波處的渦旋結構明顯的反演出來，
並且驗證了 Liou (2002) 經由數學理論所推導出來的結論，亦即增加時間解析度
能夠改善風場低估的情形，進而提升了反演風場的品質。另外，本文也利用切向
風分量佔所有風場的比例來判斷風場反演的優劣 ， 經由本文所選的個案資料，也
驗證了該指數確實可以當作判斷風場反演品質的指標。;
This is the first study of using phased array radar data to investigate the quality
and accuracy of retrieved wind field among different time resolution in Taiwan.
A single-Doppler radar velocity retrieval method, based on an optimally
determined moving frame of reference, is developed. This method enables the recovery
of the complete three-dimensional wind field using reflectivity, and radial wind
observations, detected by a single Doppler radar over multiple volume scans. This
method first computes a set of optimal moving speeds (U, V, W), which can be
functions of the height. The perturbation velocities (u′, v′, w′) are then solved
simultaneously, with respect to the moving speeds, by minimizing a cost function
through the three-dimensional variational (3D-Var) approach. Finally, by adding the
optimal moving speed to the perturbation velocities, a complete three-dimensional wind
field is obtained.
An Observation System Simulation Experiment (OSSE) is conducted to examine
the different time resolution retrieval results from single-Doppler radar observed radial
wind and reflectivity simulated by WRF model. The retrieved results show both of the
different time resolution experiments can retrieval the three-dimensional wind field
accurately and by increasing time resolution can promote the quality of the retrieval
wind field.
In addition, a supercell case during VORTEX2 on 5 June 2009 is investgated in
this study. We use MWR-05XP radar data, which is phased array radar, DOW6 radar
data and DOW7 radar data to test and verify by single-Doppler velocity retrieval
method. The results reveal both different time resolution experiments can retrieve the
vortex structure clearly and by increasing time resolution can promote the quality of
the retrieval wind field and reduce the underestimate of the azimuthal wind field. The
iii retrieval results also verify the index (AoR) can be used to determine the quality of the
retrieval wind field. |
