At 0247 UTC 13 February 2013, a South Korean commercial aircraft encountered moderate-level clear-air turbulence at ~24 000 ft (~7.3 km) over the Yellow Sea (121.25°E, 38.55°N) en route from Incheon, South Korea, to Tianjin, China. Two crew members were severely injured by this event. To investigate the possible mechanisms of this event, a high-resolution numerical simulation using the Weather Research and Forecasting Model was conducted. In the synoptic-scale flow pattern, one of two bifurcated jet streams passed over the Yellow Sea, and strong horizontal and vertical gradients of the wind occurred on the northern edge of the jet stream near the flight route. An upper-level frontal system on the cyclonic shear side of the jet intensified as it moved northward toward a strengthening upper-level trough in northeastern China. The developed jet- frontal system induced strong vertical wind shear and tropopause folding, which extended down to about z = 5 km, near the observed turbulence region. Despite a relatively high stability with an intrusion of stratospheric air with tropopause folding, the strong vertical wind shear led to a small Richardson number in the incident region, which in turn induced the aviation turbulence through the Kelvin-Helmholtz instability. Although small-scale mountain waves were evident during the passage of flight before the incident time, breaking of these waves was not likely the key factor for the observed turbulence, given that the wave amplitudes were weak and that the strong zonal wind on the upstream of the mountain waves prohibited wave saturation and breakdown.
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Acknowledgments. The authors thank Dr. Michael Kaplan and two anonymous reviewers for their providing valuable comments and suggestions on the paper. This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMIPA 2015-1080.
© 2018 American Meteorological Society.
All Science Journal Classification (ASJC) codes
- Atmospheric Science