以數值模式資料驗證氣壓、溫度擾動場反求法

Verification of Doppler Retrieval Technique by Using A 3-D Cloud Model

林宏聖(Hang-Sen Lin) ； 陳台琦(Tai-Chi Chen Wang)

《大氣科學》 15卷2期 (1987/10) Pp. 215-232

摘要

利用多個都譜勒雷達來觀測中尺度天氣系統，可以獲得詳細的三維風場結構，但對於動力而言，都譜勒雷達是無法提供氣壓、溫度的觀測。Gal-Chen（1978）提出利用風場經由動量方程式來計算氣壓、溫度擾動場的方法，由方法本身提供特有的邊界條件（即Neumann邊界條件），此方法稱為熱動力反求法（thermodynamic retrieval method）。本文乃是利用Wilhelmson and Chen（1982）所建立之三維數值雲模式的輸出資料來驗證熱動力反求法。以模式風場作為觀測風場，經由熱動力反求法計算氣壓、位溫擾動場偏差量。整體而言，反求法計算之氣壓、位溫擾動場偏差量之分佈與模式十分接近，在風場梯度的空間變化較弱區有較佳的反求結果，反之，較強區反求結果則較差；顯示，反求結果之誤差的大小與風場梯度及網格解析度有關：風場變化大時，造成強迫項（forcing term）空間分佈變化大，且在網格解析度不佳情況下，數值方法無法解析出強迫項的變化所致。而當壓力場有誤差時，由垂直氣壓梯度反求之浮力場將會有較大之誤差。在未來，將以不同的風場資料組及解析度來測試強迫項的分佈與解析度間的關係對反求結果正確性的影響。

關鍵字

都譜勒雷達風場 ； 熱力場 ； 反求法

並列摘要

Multiple Doppler radars observations can provide detail wind measurements within a precipitation system. But there is no direct measurements of dynamic and thermodynamic field except very few airplane penetrations. An indirect retrieval method was suggested by Gal-Chen (1978) to calculate perturbation pressure and density field from Doppler wind.Gal-Chen and Kropfli (1984), Roux et al. (1984), Hane and Ray (1985), Lin et al. (1986) applied this technique to real data case studies. Their results indicated that the retrieved dynamic structure are consistent with kinematic field. However, the retrieved perturbation field is the deviation from a unknown horizontal mean value, the results were difficult to be verified.Through a 3-D numerical cloud model (Wilhelmson and Chen, 1982), tue model output wind field were used as data in the momentum equations to retrieve perturbation pressure and virtual temperature. Overall the retrieved pattern are very similar to the model's. At lower and middle levels, the maximum center location and maximum value match very well. At upper levels, some distortion happened. The location of these erroneous perturbation pressure is associated with the large spatial variation in the forcing term distribution which was deduced from the strong wind gradient.The perturbation pressure center position shift lead to erroneous temperature field at upper levels.In order to find out the relation between proper resolution for different forcing terms distribution, more test will be done in the near future.

並列關鍵字

Doppler wind ； thermodynamic field ； retrieval