使用VAD方法及雷達回波資料估計大氣垂直渦度剖線

本研究利用傳統的都卜勒氣象雷達VAD(Velocity Azimuth Display)分析技術，並結合一個雷達回波保守方程，來估計原有VAD方法無法計算的渦度場(Vorticity)垂直分量的垂直分佈剖線(Profile)。為驗證本方法的精確度，吾人設計一個由Rankine Vortex所產生的理想颱風模式資料來加以檢驗，經由比較理論值與反演值的結果，可看出本方法在定量及定性上的估計均有相當不錯的表現。本研究中將此改良後的VAD方法應用在納莉颱風(2001)及艾利颱風(2004)的個案中。在納莉颱風個案中，吾人發現如同理論分析所顯示的，隨著颱風的靠近，垂直渦度亦隨之增加，其變化的趨勢與模擬結果極為相似，這代表本方法適用於真實個案的分析。在艾利颱風個案中，吾人亦將時降雨量納入討論，發現渦度場與輻合輻散場與地面時降雨量存在對應的關係，在若干時時段中，輻合的增加與正渦度的增強，會領先地面降雨極值出現的時機，可能具有某種極短期預報上的意義，但仍需更多研究加以確認。

關鍵字

VAD ；渦度場；極短期預報

並列摘要

In this study the traditional Velocity Azimuth Display (VAD) method used for Doppler radar data analysis is further modified by combining it with a radar reflectivity conservation equation. With this modification, it becomes possible to estimate the vertical distribution of the vorticity, which is a quantity not recoverable with the original VAD formulation. In order to validate the accuracy of this modified method, an idealized typhoon circulation is constructed using the Rankine vortex model. A detailed inter-comparison indicates that the retrieved results produced by this modified VAD method agree favorably well with the analytic solutions both qualitatively and quantitatively. This newly modified method is then applied to analyze two real cases-Typhoon Nan (2001) and Typhoon Aere (2004). In the case of Nan, the vertical vorticity increases as the typhoon approaching the radar, which is similar to the results revealed by theoretic analyses. This experiment indicates that the application of the modified VAD to real case study is feasible. In the case of Aere, the increase of the horizontal convergence and the vertical vorticity is found to correspond or lead the appearance of a heavy rain fall. However, whether the structural changes can truly be used in a short-term predication requires more studies.

並列關鍵字

Velocity Azimuth Display ； Vorticity ； Short-term predication

國際替代計量

使用VAD方法及雷達回波資料估計大氣垂直渦度剖線

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