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

• Main Authors: Kai-Yuan Cheng, 鄭凱元
• Other Authors: 林博雄
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/58273570993871941769

碩士 === 國立臺灣大學 === 大氣科學研究所 === 98 === 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.