對流引發內重力波之模擬與晴空亂流個案診斷應用

The Simulation of Internal Gravity Waves Induced by Convective Systems and Its Application to Clear-air Turbulence Diagnostics

鄭凱元(Kai-Yuan Cheng)

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.2010.02474

摘要

對流系統所引發的向上向外傳播之重力波擾動，被認為是飛機遭遇晴空亂流之可能肇因之一。本研究試圖建立對流系統造成亂流飛航事故之診斷流程，首先透過WRF大氣數值模式提供WISCDYMM雲物理動力模式的初始剖面，進行時間和空間降尺度的天氣情境模擬，過程中藉由二維波譜來分析對流系統產生重力波之傳播特徵，並利用渦流消散速率 (EDR1/3) 來定量估計重力波造成之亂流強度。本研究選擇2008年秋天CI-641航班在泰國曼谷機場東北方上空12 km，以及2005年春天BR-2196航班在日本東岸上空10 km，以這兩個晴空亂流飛安事件個案做為重力波引發亂流的診斷分析對象。
模擬結果發現，在重力波方面，對流系統引發之重力波自對流中心激發，朝四面八方傳播之現象。CI-641個案重力波在高度11 ~ 18 km傳播，與航空器巡航空層相穩合；BR-2196個案之重力波在高度4 ~ 8 km傳播，較航空器巡航空層低約2 km。在亂流強度部分，EDR1/3空間分佈顯現重力波傳播的特徵，而CI-641個案之巡航空層最大EDR1/3約0.127，顯示輕度亂流訊號；BR-2196個案之巡航空層最大EDR1/3約0.0035，沒有亂流訊號。因此，我們認為對流系統引發之重力波可能是造成CI-641事故的原因，至於BR-2196事件與對流系統應無關聯性。

關鍵字

晴空亂流 ； 重力波 ； 對流系統

並列摘要

The gravity waves induced by convective system could play a role in triggering clear-air turbulence (CAT). This study attempted to establish the diagnostic procedure of CAT accidents caused by convectively gravity waves. To recognize sufficient details of the convectively gravity waves, an explicit cloud-scale model WISCDYMM with its initial profile provided by meso-scale WRF model was utilized to reproduce weather scenario. Two-dimensional spectral analysis was used to identify the characteristics of gravity waves in this study. Furthermore, in order to quantify the CAT intensity, eddy dissipation rate (EDR1/3) was calculated based on WISCDYMM model outputs in the cases simulation.
To explore this procedure, two CAT accidents were selected for case study. The first one was CI-641 accident, which happened at 12 km over the northeast of Bangkok airport in Thailand in the summer of 2008; the other was BR-2196 accident, which happened at 10 km over the east coast of Japan in the spring of 2005.
The simulations indicated that convective systems made gravity waves propagate outward from convection center. In Case CI-641, the gravity wave propagated at a height of 11 ~ 18 km, which was concurrent with the layer where aircraft cruised; in Case BR-2196, the gravity wave propagated at a height of 4 ~ 8 km, about 2 km lower than the layer where aircraft cruised. In terms of turbulence intensity, EDR1/3 showed the pattern of the turbulence distribution caused by the propagation of gravity waves. In Case CI-641, the largest EDR1/3 at aircraft patrolling layers was about 0.127, indicating light level of turbulence. In Case BR-2196, the maximum of EDR1/3 was about 0.0035, indicating no occurrence of turbulence. The results suggest that the gravity waves induced by convective systems could be used to explain the cause of the CAT accident in Case CI-641. In contrast, BR-2196 accident may have no association with convective systems.

並列關鍵字

clear-air turbulence ； gravity wave ； convective systems

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