A Numerical Study on Convectively Induced Turbulence (CIT) Encounter above a Dissipating Deep Convection

On 2 September 2007, a commercial aircraft en route from Jeju, Korea to Osaka, Japan encountered severe turbulence near Fukuoka at its cruising altitude of 35000 ft (about z = 11.2 km) at 1034 UTC. According to the evolution of brightness temperature obtained from the Multi-functional Satellite (MTSAT) data, an isolated deep convection was in the dissipating stage, which is likely related to the turbulence encounter. To investigate the characteristics and generation mechanisms of the turbulence event, three-dimensional real atmosphere is simulated by the Weather Research and Forecasting (WRF) model with six nested domains with the finest horizontal grid spacing of 120 m. Location and timing of the observed turbulence along the evolving deep convection and large-scale flow appeared in available observations are reasonably well reproduced in the model results. In synoptic condition, low pressure system is being strengthening as eastward upper-level trough approaches. Single-cell type of a deep convection develops in a warm area ahead the cold front in the southwestern region of the turbulence at 4 hrs before the incident time. Isolated updrafts penetrating tropopause reaches up to z = 14.4 km, and then the cloud top decreases significantly as the upward motion in the convection becomes weakened in the dissipating stage. As southwesterly passes through the dissipating convection, flows are disturbed and vertical wind shear is enhanced on the lee-side of the convection. A leading edge of the cloud top stretches toward the lee-side and is finally overturned due to the entrainment of the environmental air into the cloud. The turbulence is activated through the convective instability in the entrainment process. At the incident time, the simulated turbulence remains at 1 km above the dissipating convection, which passes through the location of the observed turbulence.