本研究主要目的為同化衛星近海表面風場以改善洋面低層大氣之三維 動力場，因此設計一系列實驗組檢驗其帶來之效益。透過觀測系統模擬實 驗(Observing Systems Simulation Experiment, OSSE)，並利用多都卜勒雷達 風 場 合 成 方 法 (WInd Synthesis System using Doppler Measurement, WISSDOM)，以數學變分法極小化各項約束條件以反演三維風場，故設計 二理想個案探討同化衛星近海表面風場並搭配雷達觀測以檢驗對底層三維 風場之影響，第一個是2013年06月23日在台灣南部外海之西南氣流個案， 第二個是2017年06月01日在台灣北部外海之梅雨系統個案。 西南氣流個案結果說明同化衛星觀測風向及風速能大幅改善第一層水 平風場，並將其資訊向上傳遞至較高層大氣;梅雨系統個案則顯示只同化 衛星觀測風速對風速能夠大幅改善，但對底層大氣改善程度有限。從二理 想個案指出同化衛星觀測點數量越高，改善底層風場的效果越佳。 本研究的優點是新增同化衛星觀測方法並改善低層大氣動力結構。並 期望未來能探討衛星觀測對熱動力場及數值天氣預報的影響。;The objective of this study is to investigate the impact of assimilation near ocean surface wind field through a series of experiments. An advanced scheme had been developed called WInd Synthesis System used to Doppler Measurements (WISSDOM) is applied to combine near ocean surface wind field with radar data through OSSE (Observing Systems Simulation Experiment) tests. The concept is based on the variational analysis, which can minimize the cost function to obtain the complete three-dimensional wind field. Two OSSEs are utilized: one is the southwest moonson case on 23 June, 2013 in southern Taiwan offshore, the other is a mei-yu frontal system on 01 June, 2017 passing northern Taiwan offshore. Results of first case indicate that assimilating both wind speed and wind direction by satellite data has a great ability to improve the three-dimensional wind field at lower atmosphere, then transport the correct information to higher levels. Second case demonstrates that only assimilating speed by satellite data can make the wind speed better, but it has limited effect on wind direction at bottom atmosphere. The more observation data are utilized, the better effect at bottom atmosphere from two cases. The advantage of this research is assimilating satellite data to improve the dynamic structure at lower atmosphere. Future objectives are to investigate the impact of satellite data on retrieving the thermodynamic field and the performance of numerical weather prediction.
