飛機積冰模擬與診斷

The Simulation and Diagnosis of Aircraft Icing

王璿瑋(Hsuan-Wei Wang)

指導教授 ： 林博雄

國立臺灣大學/理學院/大氣科學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01486

摘要

積冰對於飛航安全影響重大，也是雲物理觀測與模擬的一項科學議題。過去發生的航空器積冰事件的統計結果發現，積冰發生的有效環境溫度介於-3~-15°C，而且很少低於-25°C以下。從環境溼度的統計發現，相對溼度必須超過70%以上才有較高的機率產生積冰。研究文獻指出，積冰預測以及民用航空器的積冰警告系統，大多直接從溫度與相對溼度兩參數(T-RH algorithm)加以推測，因此航空氣象作業單位直接利用中尺度天氣數值模式之輸出參數來估算積冰(Thompson et al. 1997; Schultz and Politovich 1992; Knapp 1992)。綜合言之，綜觀大氣背景環境以及液態水含量(LWC)的掌握是判斷積冰潛勢(Icing Potential)的必要條件。
本文透過美國航空Eagle-4184航班個案(1994年10月31日15:57UTC)以及復興航空GE-791航班個案(2002年12月20日17:52UTC)，嘗試使用WRF中尺度模式和WISCDYMM雲物理動力模式，來模擬診斷這兩次嚴重的ATR-72飛機積冰的大氣環境和數值模式預報能力。在Eagle-4184個案模擬中，WRF在綜觀環境場的模擬結果跟美國天氣服務(NWS)所發布的地面天氣圖是相當一致，飛行高度10,000呎的環境溫度-2℃，西南風，風速約為20ms-1。從WISCDYMM雲模式所提供的高時空解析參數中，進行液態水含量的計算，得知飛行空層LWC都超過0.24(g kg-1)，而且有局部的區域超過0.36(g kg-1)，屬於輕度到中度強度的積冰。在GE-791個案中，利用WRF輸出參數進行LWC計算，模擬出飛行路徑上LWC大約介於0.05 ~ 0.15 (g kg-1)，積冰訊號並不明顯，但是使用WISCDYMM診斷空難發生空域的LWC，由模式模擬出17:49UTC的LWC高達0.2(k/kg)，相對於WRF的模擬結果更為顯著。另外，在17:34UTC以及17:49UTC兩時段的雷達回波有出現峰值，這兩筆回波峰值訊號出現的時間點跟WISCDYMM所模擬出的LWC高值的時間點相符。
WRF模式模擬結果顯示，綜觀與中尺度天氣條件大致掌握這兩個案飛機的盤旋與巡航高度之LWC大於氣候平均值的特徵，WISCDYMM模式則進一步提供了更高時間與空間解析度的環境場，可以用檢視飛機失事前數十分鐘期間的大氣溫度場以及LWC空間分布，進而估算飛行航路上的積冰程度。

關鍵字

積冰 ； 液態水含量 ； 雲模式

並列摘要

Icing plays a significant role in the issue of fight safety, and it’s also an important issue of microphysical observation and model simulation in meteorology. In the literatures, the current icing forecasting and warning system only use temperature and relative humidity parameters. But the over-prediction of the spatial extent of aircraft icing has reduced the reference for flight path planning. Some research found Icing intensity can deduce from estimation of liquid water content (LWC), and the U.S. NOAA/NWS icing forecasting production for United States Route is referential. Before 2006, the icing forecasting from Taipei Flight Information Region (Taipei FIR) stayed the icing prediction by temperature and relative humidity, and then used the NCAR product directly until now. It is necessary that we should explore more on the microphysical simulation and application of Taiwan.
American Airline Flight Eagle-4184 encountered icing when it was holding at 10,000 ft, then the flight lost control and crashed at 15:57 UTC, October 31 of 1994 near Roselawn, Indiana. It was the first loss of an ATR 72 aircraft in the world. In Taiwan, TransAsia Airways cargo flight GE-791 encountered serve icing and crashed off the coast of southwest Makung at 15:52UTC, October 21 of 2002. It led to weather forecaster litigation. In this study, we focus on the small and mesoscale weather diagnosis and icing potential forecast. First, WRF (Weather Research and Forecasting Model V3.1) is used to analyze the environmental field. Then we implant WRF output into WISCDYMM (Wisconsin Dynamic-Microphysical Model), and diagnose these two cases with WISCDYMM high spatial and temporal resolution (1.0 km horizontally, 0.2 km vertically, 2 sec time step). The 1 km thickness of LWC parameter in Flight Air Layer (18000 feet) is computed and compared with weather radar and Infrared satellite image date.
The results showed that the LWC simulated from WRF is 0.1~0.2 (g/kg) in two cases, it only arrived at a weak icing level. From WISCDYMM simulation in lasted 10 minutes of Eagle-4184 , the atmospheric environment was cold and rainy. This might be the reason why the plane cannot de-ice clearly. Comparison of radar data and LWC simulation in GE-791 case, LWC has an increasing trend before the radar reflection increased. It shows that WISCDYMM cloud model under WRF mesoscale simulation has good performance for diagnosing the small scale feature for aviation weather watch.

並列關鍵字

Icing ； Liquid Water Content ； WISCDYMM

參考文獻

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